From 9beb60c71370182fb6004a7019c550fd919498d3 Mon Sep 17 00:00:00 2001
From: Jiancheng Chen <2742581175@qq.com>
Date: Thu, 18 Aug 2022 11:22:36 +0800
Subject: [PATCH 1/8] improve error messages in
 change_box,create_box,domain,input,lattice and neighbor.cpp

---
 src/change_box.cpp | 35 ++++++++++++++---------------
 src/create_box.cpp | 22 +++++++++---------
 src/domain.cpp     |  6 ++---
 src/input.cpp      |  8 +++----
 src/lattice.cpp    | 56 +++++++++++++++++++++++++---------------------
 src/neighbor.cpp   |  6 ++---
 6 files changed, 69 insertions(+), 64 deletions(-)

diff --git a/src/change_box.cpp b/src/change_box.cpp
index 08af5f11c9..b26d7803ed 100644
--- a/src/change_box.cpp
+++ b/src/change_box.cpp
@@ -46,14 +46,14 @@ void ChangeBox::command(int narg, char **arg)
 
   if (domain->box_exist == 0)
     error->all(FLERR,"Change_box command before simulation box is defined");
-  if (narg < 2) error->all(FLERR,"Illegal change_box command");
+  if (narg < 2) utils::missing_cmd_args(FLERR, "change_box", error);
 
   if (comm->me == 0) utils::logmesg(lmp,"Changing box ...\n");
 
   // group
 
   int igroup = group->find(arg[0]);
-  if (igroup == -1) error->all(FLERR,"Could not find change_box group ID");
+  if (igroup == -1) error->all(FLERR,"Could not find change_box group ID {}", arg[0]);
   int groupbit = group->bitmask[igroup];
 
   // parse operation arguments
@@ -70,7 +70,7 @@ void ChangeBox::command(int narg, char **arg)
   while (iarg < narg) {
     if (strcmp(arg[iarg],"x") == 0 || strcmp(arg[iarg],"y") == 0 ||
         strcmp(arg[iarg],"z") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal change_box command");
+      if (iarg+2 > narg) error->all(FLERR, "Illegal change_box {} command: missing argument(s)", arg[iarg]);
       ops[nops].style = XYZ;
       if (strcmp(arg[iarg],"x") == 0) ops[nops].dim = X;
       else if (strcmp(arg[iarg],"y") == 0) ops[nops].dim = Y;
@@ -80,7 +80,7 @@ void ChangeBox::command(int narg, char **arg)
         error->all(FLERR,"Cannot change_box in z dimension for 2d simulation");
 
       if (strcmp(arg[iarg+1],"final") == 0) {
-        if (iarg+4 > narg) error->all(FLERR,"Illegal change_box command");
+        if (iarg+4 > narg) error->all(FLERR, "Illegal change_box {} final command: missing argument(s)", arg[iarg]);
         ops[nops].flavor = FINAL;
         ops[nops].flo = utils::numeric(FLERR,arg[iarg+2],false,lmp);
         ops[nops].fhi = utils::numeric(FLERR,arg[iarg+3],false,lmp);
@@ -88,7 +88,7 @@ void ChangeBox::command(int narg, char **arg)
         nops++;
         iarg += 4;
       } else if (strcmp(arg[iarg+1],"delta") == 0) {
-        if (iarg+4 > narg) error->all(FLERR,"Illegal change_box command");
+        if (iarg+4 > narg) error->all(FLERR, "Illegal change_box {} delta command: missing argument(s)", arg[iarg]);
         ops[nops].flavor = DELTA;
         ops[nops].dlo = utils::numeric(FLERR,arg[iarg+2],false,lmp);
         ops[nops].dhi = utils::numeric(FLERR,arg[iarg+3],false,lmp);
@@ -96,7 +96,7 @@ void ChangeBox::command(int narg, char **arg)
         nops++;
         iarg += 4;
       } else if (strcmp(arg[iarg+1],"scale") == 0) {
-        if (iarg+3 > narg) error->all(FLERR,"Illegal change_box command");
+        if (iarg+3 > narg) error->all(FLERR, "Illegal change_box {} scale command: missing argument(s)", arg[iarg]);
         ops[nops].flavor = SCALE;
         ops[nops].scale = utils::numeric(FLERR,arg[iarg+2],false,lmp);
         ops[nops].vdim1 = ops[nops].vdim2 = -1;
@@ -112,11 +112,11 @@ void ChangeBox::command(int narg, char **arg)
         else ops[nops-1].vdim1 = ops[nops].dim;
         iarg += 2;
 
-      } else error->all(FLERR,"Illegal change_box command");
+      } else error->all(FLERR, "Unknown change_box {} argument: {}", arg[iarg], arg[iarg+1]);
 
     } else if (strcmp(arg[iarg],"xy") == 0 || strcmp(arg[iarg],"xz") == 0 ||
         strcmp(arg[iarg],"yz") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal change_box command");
+      if (iarg+2 > narg) error->all(FLERR, "Illegal change_box {} command: missing argument(s)", arg[iarg]);
       ops[nops].style = TILT;
       if (strcmp(arg[iarg],"xy") == 0) ops[nops].dim = XY;
       else if (strcmp(arg[iarg],"xz") == 0) ops[nops].dim = XZ;
@@ -126,21 +126,21 @@ void ChangeBox::command(int narg, char **arg)
         error->all(FLERR,"Cannot change_box in xz or yz for 2d simulation");
 
       if (strcmp(arg[iarg+1],"final") == 0) {
-        if (iarg+3 > narg) error->all(FLERR,"Illegal change_box command");
+        if (iarg+3 > narg) error->all(FLERR, "Illegal change_box {} final command: missing argument(s)", arg[iarg]);
         ops[nops].flavor = FINAL;
         ops[nops].ftilt = utils::numeric(FLERR,arg[iarg+2],false,lmp);
         nops++;
         iarg += 3;
       } else if (strcmp(arg[iarg+1],"delta") == 0) {
-        if (iarg+3 > narg) error->all(FLERR,"Illegal change_box command");
+        if (iarg+3 > narg) error->all(FLERR, "Illegal change_box {} delta command: missing argument(s)", arg[iarg]);
         ops[nops].flavor = DELTA;
         ops[nops].dtilt = utils::numeric(FLERR,arg[iarg+2],false,lmp);
         nops++;
         iarg += 3;
-      } else error->all(FLERR,"Illegal change_box command");
+      } else error->all(FLERR, "Unknown change_box {} argument: {}", arg[iarg], arg[iarg+1]);
 
     } else if (strcmp(arg[iarg],"boundary") == 0) {
-      if (iarg+4 > narg) error->all(FLERR,"Illegal change_box command");
+      if (iarg+4 > narg) utils::missing_cmd_args(FLERR, "change_box boundary", error);
       ops[nops].style = BOUNDARY;
       ops[nops].boundindex = iarg+1;
       nops++;
@@ -157,7 +157,6 @@ void ChangeBox::command(int narg, char **arg)
       iarg += 1;
 
     } else if (strcmp(arg[iarg],"set") == 0) {
-      if (iarg+1 > narg) error->all(FLERR,"Illegal change_box command");
       ops[nops].style = SET;
       nops++;
       iarg += 1;
@@ -170,7 +169,7 @@ void ChangeBox::command(int narg, char **arg)
     } else break;
   }
 
-  if (nops == 0) error->all(FLERR,"Illegal change_box command");
+  if (nops == 0) error->all(FLERR, "Unknown change_box keyword: {}", arg[iarg]);
 
   // move_atoms = 1 if need to move atoms to new procs after box changes
   // anything other than ORTHO or TRICLINIC may cause atom movement
@@ -393,19 +392,19 @@ void ChangeBox::command(int narg, char **arg)
 
 void ChangeBox::options(int narg, char **arg)
 {
-  if (narg < 0) error->all(FLERR,"Illegal change_box command");
+  if (narg < 0) utils::missing_cmd_args(FLERR, "change_box", error);
 
   scaleflag = 1;
 
   int iarg = 0;
   while (iarg < narg) {
     if (strcmp(arg[iarg],"units") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal change_box command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "change_box units", error);
       if (strcmp(arg[iarg+1],"box") == 0) scaleflag = 0;
       else if (strcmp(arg[iarg+1],"lattice") == 0) scaleflag = 1;
-      else error->all(FLERR,"Illegal change_box command");
+      else error->all(FLERR, "Invalid change_box units argument: {}", arg[iarg+1]);
       iarg += 2;
-    } else error->all(FLERR,"Illegal change_box command");
+    } else error->all(FLERR,"Unknown change_box keyword: {}", arg[iarg]);
   }
 }
 
diff --git a/src/create_box.cpp b/src/create_box.cpp
index cd6a63ca44..b05bfe0825 100644
--- a/src/create_box.cpp
+++ b/src/create_box.cpp
@@ -35,7 +35,7 @@ CreateBox::CreateBox(LAMMPS *lmp) : Command(lmp) {}
 
 void CreateBox::command(int narg, char **arg)
 {
-  if (narg < 2) error->all(FLERR, "Illegal create_box command");
+  if (narg < 2) utils::missing_cmd_args(FLERR, "create_box", error);
 
   if (domain->box_exist) error->all(FLERR, "Cannot create_box after simulation box is defined");
   if (domain->dimension == 2 && domain->zperiodic == 0)
@@ -107,56 +107,56 @@ void CreateBox::command(int narg, char **arg)
   int iarg = 2;
   while (iarg < narg) {
     if (strcmp(arg[iarg], "bond/types") == 0) {
-      if (iarg + 2 > narg) error->all(FLERR, "Illegal create_box command");
+      if (iarg + 2 > narg) utils::missing_cmd_args(FLERR, "create_box bond/type", error);
       if (!atom->avec->bonds_allow) error->all(FLERR, "No bonds allowed with this atom style");
       atom->nbondtypes = utils::inumeric(FLERR, arg[iarg + 1], false, lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg], "angle/types") == 0) {
-      if (iarg + 2 > narg) error->all(FLERR, "Illegal create_box command");
+      if (iarg + 2 > narg) utils::missing_cmd_args(FLERR, "create_box angle/types", error);
       if (!atom->avec->angles_allow) error->all(FLERR, "No angles allowed with this atom style");
       atom->nangletypes = utils::inumeric(FLERR, arg[iarg + 1], false, lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg], "dihedral/types") == 0) {
-      if (iarg + 2 > narg) error->all(FLERR, "Illegal create_box command");
+      if (iarg + 2 > narg) utils::missing_cmd_args(FLERR, "create_box dihedral/types", error);
       if (!atom->avec->dihedrals_allow)
         error->all(FLERR, "No dihedrals allowed with this atom style");
       atom->ndihedraltypes = utils::inumeric(FLERR, arg[iarg + 1], false, lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg], "improper/types") == 0) {
-      if (iarg + 2 > narg) error->all(FLERR, "Illegal create_box command");
+      if (iarg + 2 > narg) utils::missing_cmd_args(FLERR, "create_box improper/types", error);
       if (!atom->avec->impropers_allow)
         error->all(FLERR, "No impropers allowed with this atom style");
       atom->nimpropertypes = utils::inumeric(FLERR, arg[iarg + 1], false, lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg], "extra/bond/per/atom") == 0) {
-      if (iarg + 2 > narg) error->all(FLERR, "Illegal create_box command");
+      if (iarg + 2 > narg) utils::missing_cmd_args(FLERR, "create_box extra/bond/per/atom", error);
       if (!atom->avec->bonds_allow) error->all(FLERR, "No bonds allowed with this atom style");
       atom->bond_per_atom = utils::inumeric(FLERR, arg[iarg + 1], false, lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg], "extra/angle/per/atom") == 0) {
-      if (iarg + 2 > narg) error->all(FLERR, "Illegal create_box command");
+      if (iarg + 2 > narg) utils::missing_cmd_args(FLERR, "create_box extra/angle/per/atom", error);
       if (!atom->avec->angles_allow) error->all(FLERR, "No angles allowed with this atom style");
       atom->angle_per_atom = utils::inumeric(FLERR, arg[iarg + 1], false, lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg], "extra/dihedral/per/atom") == 0) {
-      if (iarg + 2 > narg) error->all(FLERR, "Illegal create_box command");
+      if (iarg + 2 > narg) utils::missing_cmd_args(FLERR, "create_box extra/dihedral/per/atom", error);
       if (!atom->avec->dihedrals_allow)
         error->all(FLERR, "No dihedrals allowed with this atom style");
       atom->dihedral_per_atom = utils::inumeric(FLERR, arg[iarg + 1], false, lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg], "extra/improper/per/atom") == 0) {
-      if (iarg + 2 > narg) error->all(FLERR, "Illegal create_box command");
+      if (iarg + 2 > narg) utils::missing_cmd_args(FLERR, "create_box extra/improper/per/atom", error);
       if (!atom->avec->impropers_allow)
         error->all(FLERR, "No impropers allowed with this atom style");
       atom->improper_per_atom = utils::inumeric(FLERR, arg[iarg + 1], false, lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg], "extra/special/per/atom") == 0) {
-      if (iarg + 2 > narg) error->all(FLERR, "Illegal create_box command");
+      if (iarg + 2 > narg) utils::missing_cmd_args(FLERR, "create_box extra/special/per/atom", error);
       force->special_extra = utils::inumeric(FLERR, arg[iarg + 1], false, lmp);
       atom->maxspecial += force->special_extra;
       iarg += 2;
     } else
-      error->all(FLERR, "Illegal create_box command");
+      error->all(FLERR, "Unknown create_box keyword: {}", arg[iarg]);
   }
 
   // problem setup using info from header
diff --git a/src/domain.cpp b/src/domain.cpp
index ebc468faed..7d60c20a24 100644
--- a/src/domain.cpp
+++ b/src/domain.cpp
@@ -1856,7 +1856,7 @@ const std::vector<Region *> Domain::get_region_list()
 
 void Domain::set_boundary(int narg, char **arg, int flag)
 {
-  if (narg != 3) error->all(FLERR,"Illegal boundary command");
+  if (narg != 3) error->all(FLERR,"Illegal boundary command: expected 3 argument but found {}", narg);
 
   char c;
   for (int idim = 0; idim < 3; idim++)
@@ -1870,8 +1870,8 @@ void Domain::set_boundary(int narg, char **arg, int flag)
       else if (c == 's') boundary[idim][iside] = 2;
       else if (c == 'm') boundary[idim][iside] = 3;
       else {
-        if (flag == 0) error->all(FLERR,"Illegal boundary command");
-        if (flag == 1) error->all(FLERR,"Illegal change_box command");
+        if (flag == 0) error->all(FLERR,"Unknown boundary keyword: {}", c);
+        if (flag == 1) error->all(FLERR,"Unknown change_box keyword: {}", c);
       }
     }
 
diff --git a/src/input.cpp b/src/input.cpp
index 2979503d30..bb84a86e2c 100644
--- a/src/input.cpp
+++ b/src/input.cpp
@@ -1351,7 +1351,7 @@ void Input::atom_modify()
 
 void Input::atom_style()
 {
-  if (narg < 1) error->all(FLERR,"Illegal atom_style command");
+  if (narg < 1) utils::missing_cmd_args(FLERR, "atom_style", error);
   if (domain->box_exist)
     error->all(FLERR,"Atom_style command after simulation box is defined");
   atom->create_avec(arg[0],narg-1,&arg[1],1);
@@ -1488,12 +1488,12 @@ void Input::dihedral_style()
 
 void Input::dimension()
 {
-  if (narg != 1) error->all(FLERR,"Illegal dimension command");
+  if (narg != 1) error->all(FLERR,"Illegal dimension command: expected 1 argument but found {}", narg);
   if (domain->box_exist)
     error->all(FLERR,"Dimension command after simulation box is defined");
   domain->dimension = utils::inumeric(FLERR,arg[0],false,lmp);
   if (domain->dimension != 2 && domain->dimension != 3)
-    error->all(FLERR,"Illegal dimension command");
+    error->all(FLERR, "Invalid dimension argument: {}", arg[0]);
 
   // must reset default extra_dof of all computes
   // since some were created before dimension command is encountered
@@ -1948,7 +1948,7 @@ void Input::unfix()
 
 void Input::units()
 {
-  if (narg != 1) error->all(FLERR,"Illegal units command");
+  if (narg != 1) error->all(FLERR,"Illegal units command: expected 1 argument but found {}", narg);
   if (domain->box_exist)
     error->all(FLERR,"Units command after simulation box is defined");
   update->set_units(arg[0]);
diff --git a/src/lattice.cpp b/src/lattice.cpp
index be69fc1821..f88a55a4d5 100644
--- a/src/lattice.cpp
+++ b/src/lattice.cpp
@@ -36,7 +36,7 @@ Lattice::Lattice(LAMMPS *lmp, int narg, char **arg) : Pointers(lmp)
 
   // parse style arg
 
-  if (narg < 1) error->all(FLERR,"Illegal lattice command");
+  if (narg < 1) utils::missing_cmd_args(FLERR, "lattice", error);
 
   if (strcmp(arg[0],"none") == 0) style = NONE;
   else if (strcmp(arg[0],"sc") == 0) style = SC;
@@ -48,10 +48,10 @@ Lattice::Lattice(LAMMPS *lmp, int narg, char **arg) : Pointers(lmp)
   else if (strcmp(arg[0],"sq2") == 0) style = SQ2;
   else if (strcmp(arg[0],"hex") == 0) style = HEX;
   else if (strcmp(arg[0],"custom") == 0) style = CUSTOM;
-  else error->all(FLERR,"Illegal lattice command");
+  else error->all(FLERR,"Unknown lattice keyword: {}", arg[0]);
 
   if (style == NONE) {
-    if (narg != 2) error->all(FLERR,"Illegal lattice command");
+    if (narg != 2) error->all(FLERR,"Illegal lattice command: expected 2 argument but found {}", narg);
 
     // Domain creates a default lattice of style "none"
     //   before Force class is instantiated, just use atof() in that case
@@ -61,7 +61,7 @@ Lattice::Lattice(LAMMPS *lmp, int narg, char **arg) : Pointers(lmp)
     else
       xlattice = ylattice = zlattice = atof(arg[1]);
 
-    if (xlattice <= 0.0) error->all(FLERR,"Illegal lattice command");
+    if (xlattice <= 0.0) error->all(FLERR, "Invalid lattice none argument: {}", arg[1]);
     return;
   }
 
@@ -81,9 +81,9 @@ Lattice::Lattice(LAMMPS *lmp, int narg, char **arg) : Pointers(lmp)
 
   // scale = conversion factor between lattice and box units
 
-  if (narg < 2) error->all(FLERR,"Illegal lattice command");
+  if (narg < 2) utils::missing_cmd_args(FLERR, "lattice", error);
   scale = utils::numeric(FLERR,arg[1],false,lmp);
-  if (scale <= 0.0) error->all(FLERR,"Illegal lattice command");
+  if (scale <= 0.0) error->all(FLERR, "Invalid lattice {} argument: {}", arg[0], arg[1]);
 
   // set basis atoms for each style
   // x,y,z = fractional coords within unit cell
@@ -148,23 +148,25 @@ Lattice::Lattice(LAMMPS *lmp, int narg, char **arg) : Pointers(lmp)
   int iarg = 2;
   while (iarg < narg) {
     if (strcmp(arg[iarg],"origin") == 0) {
-      if (iarg+4 > narg) error->all(FLERR,"Illegal lattice command");
+      if (iarg+4 > narg) utils::missing_cmd_args(FLERR, "lattice origin", error);
       origin[0] = utils::numeric(FLERR,arg[iarg+1],false,lmp);
       origin[1] = utils::numeric(FLERR,arg[iarg+2],false,lmp);
       origin[2] = utils::numeric(FLERR,arg[iarg+3],false,lmp);
-      if (origin[0] < 0.0 || origin[0] >= 1.0 ||
-          origin[1] < 0.0 || origin[1] >= 1.0 ||
-          origin[2] < 0.0 || origin[2] >= 1.0)
-        error->all(FLERR,"Illegal lattice command");
+      if (origin[0] < 0.0 || origin[0] >= 1.0)
+        error->all(FLERR, "Invalid lattice origin argument: {}", origin[0]);
+      if (origin[1] < 0.0 || origin[1] >= 1.0)
+        error->all(FLERR, "Invalid lattice origin argument: {}", origin[1]);
+      if (origin[2] < 0.0 || origin[2] >= 1.0)
+        error->all(FLERR, "Invalid lattice origin argument: {}", origin[2]);
       iarg += 4;
 
     } else if (strcmp(arg[iarg],"orient") == 0) {
-      if (iarg+5 > narg) error->all(FLERR,"Illegal lattice command");
+      if (iarg+5 > narg) utils::missing_cmd_args(FLERR, "lattice orient", error);
       int dim = -1;
       if (strcmp(arg[iarg+1],"x") == 0) dim = 0;
       else if (strcmp(arg[iarg+1],"y") == 0) dim = 1;
       else if (strcmp(arg[iarg+1],"z") == 0) dim = 2;
-      else error->all(FLERR,"Illegal lattice command");
+      else error->all(FLERR,"Unknown lattice orient argument: {}", arg[iarg+1]);
       int *orient = nullptr;
       if (dim == 0) orient = orientx;
       else if (dim == 1) orient = orienty;
@@ -175,7 +177,7 @@ Lattice::Lattice(LAMMPS *lmp, int narg, char **arg) : Pointers(lmp)
       iarg += 5;
 
     } else if (strcmp(arg[iarg],"spacing") == 0) {
-      if (iarg+4 > narg) error->all(FLERR,"Illegal lattice command");
+      if (iarg+4 > narg) utils::missing_cmd_args(FLERR, "lattice spacing", error);
       spaceflag = 1;
       xlattice = utils::numeric(FLERR,arg[iarg+1],false,lmp);
       ylattice = utils::numeric(FLERR,arg[iarg+2],false,lmp);
@@ -183,46 +185,50 @@ Lattice::Lattice(LAMMPS *lmp, int narg, char **arg) : Pointers(lmp)
       iarg += 4;
 
     } else if (strcmp(arg[iarg],"a1") == 0) {
-      if (iarg+4 > narg) error->all(FLERR,"Illegal lattice command");
+      if (iarg+4 > narg) utils::missing_cmd_args(FLERR, "lattice a1", error);
       if (style != CUSTOM)
         error->all(FLERR,
-                   "Invalid option in lattice command for non-custom style");
+                   "Invalid a1 in lattice command for non-custom style");
       a1[0] = utils::numeric(FLERR,arg[iarg+1],false,lmp);
       a1[1] = utils::numeric(FLERR,arg[iarg+2],false,lmp);
       a1[2] = utils::numeric(FLERR,arg[iarg+3],false,lmp);
       iarg += 4;
     } else if (strcmp(arg[iarg],"a2") == 0) {
-      if (iarg+4 > narg) error->all(FLERR,"Illegal lattice command");
+      if (iarg+4 > narg) utils::missing_cmd_args(FLERR, "lattice a2", error);
       if (style != CUSTOM)
         error->all(FLERR,
-                   "Invalid option in lattice command for non-custom style");
+                   "Invalid a2 option in lattice command for non-custom style");
       a2[0] = utils::numeric(FLERR,arg[iarg+1],false,lmp);
       a2[1] = utils::numeric(FLERR,arg[iarg+2],false,lmp);
       a2[2] = utils::numeric(FLERR,arg[iarg+3],false,lmp);
       iarg += 4;
     } else if (strcmp(arg[iarg],"a3") == 0) {
-      if (iarg+4 > narg) error->all(FLERR,"Illegal lattice command");
+      if (iarg+4 > narg) utils::missing_cmd_args(FLERR, "lattice a3", error);
       if (style != CUSTOM)
         error->all(FLERR,
-                   "Invalid option in lattice command for non-custom style");
+                   "Invalid a3 option in lattice command for non-custom style");
       a3[0] = utils::numeric(FLERR,arg[iarg+1],false,lmp);
       a3[1] = utils::numeric(FLERR,arg[iarg+2],false,lmp);
       a3[2] = utils::numeric(FLERR,arg[iarg+3],false,lmp);
       iarg += 4;
 
     } else if (strcmp(arg[iarg],"basis") == 0) {
-      if (iarg+4 > narg) error->all(FLERR,"Illegal lattice command");
+      if (iarg+4 > narg) utils::missing_cmd_args(FLERR, "lattice basis", error);
       if (style != CUSTOM)
         error->all(FLERR,
-                   "Invalid option in lattice command for non-custom style");
+                   "Invalid basis option in lattice command for non-custom style");
       double x = utils::numeric(FLERR,arg[iarg+1],false,lmp);
       double y = utils::numeric(FLERR,arg[iarg+2],false,lmp);
       double z = utils::numeric(FLERR,arg[iarg+3],false,lmp);
-      if (x < 0.0 || x >= 1.0 || y < 0.0 || y >= 1.0 || z < 0.0 || z >= 1.0)
-        error->all(FLERR,"Illegal lattice command");
+      if (x < 0.0 || x >= 1.0)
+        error->all(FLERR, "Invalid lattice basis argument: {}", x);
+      if (y < 0.0 || y >= 1.0)
+        error->all(FLERR, "Invalid lattice basis argument: {}", y);
+      if (z < 0.0 || z >= 1.0)
+        error->all(FLERR, "Invalid lattice basis argument: {}", z);
       add_basis(x,y,z);
       iarg += 4;
-    } else error->all(FLERR,"Illegal lattice command");
+    } else error->all(FLERR,"Unknown lattice keyword: {}", arg[iarg]);
   }
 
   // check settings for errors
diff --git a/src/neighbor.cpp b/src/neighbor.cpp
index 9e74ad3809..ab77e15a4b 100644
--- a/src/neighbor.cpp
+++ b/src/neighbor.cpp
@@ -2533,10 +2533,10 @@ void Neighbor::build_one(class NeighList *mylist, int preflag)
 
 void Neighbor::set(int narg, char **arg)
 {
-  if (narg != 2) error->all(FLERR,"Illegal neighbor command");
+  if (narg != 2) error->all(FLERR,"Illegal neighbor command: expected 2 argument but found {}", narg);
 
   skin = utils::numeric(FLERR,arg[0],false,lmp);
-  if (skin < 0.0) error->all(FLERR,"Illegal neighbor command");
+  if (skin < 0.0) error->all(FLERR, "Invalid neighbor argument: {}", arg[0]);
 
   if (strcmp(arg[1],"nsq") == 0) style = Neighbor::NSQ;
   else if (strcmp(arg[1],"bin") == 0) style = Neighbor::BIN;
@@ -2544,7 +2544,7 @@ void Neighbor::set(int narg, char **arg)
     style = Neighbor::MULTI;
     ncollections = atom->ntypes;
   } else if (strcmp(arg[1],"multi/old") == 0) style = Neighbor::MULTI_OLD;
-  else error->all(FLERR,"Illegal neighbor command");
+  else error->all(FLERR,"Unknown neighbor {} argument: {}", arg[0], arg[1]);
 
   if (style == Neighbor::MULTI_OLD && lmp->citeme) lmp->citeme->add(cite_neigh_multi_old);
   if (style == Neighbor::MULTI && lmp->citeme) lmp->citeme->add(cite_neigh_multi);

From 5ff56753dafb63c74005e33e8b3e7b8f07e7032b Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Wed, 17 Aug 2022 23:56:22 -0400
Subject: [PATCH 2/8] update unit tests for changed error messages

---
 src/lattice.cpp                           |  2 +-
 unittest/commands/test_lattice_region.cpp | 28 +++++++++++++----------
 2 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/src/lattice.cpp b/src/lattice.cpp
index f88a55a4d5..14901dfa21 100644
--- a/src/lattice.cpp
+++ b/src/lattice.cpp
@@ -188,7 +188,7 @@ Lattice::Lattice(LAMMPS *lmp, int narg, char **arg) : Pointers(lmp)
       if (iarg+4 > narg) utils::missing_cmd_args(FLERR, "lattice a1", error);
       if (style != CUSTOM)
         error->all(FLERR,
-                   "Invalid a1 in lattice command for non-custom style");
+                   "Invalid a1 option in lattice command for non-custom style");
       a1[0] = utils::numeric(FLERR,arg[iarg+1],false,lmp);
       a1[1] = utils::numeric(FLERR,arg[iarg+2],false,lmp);
       a1[2] = utils::numeric(FLERR,arg[iarg+3],false,lmp);
diff --git a/unittest/commands/test_lattice_region.cpp b/unittest/commands/test_lattice_region.cpp
index 4f314b1669..cc22509dcd 100644
--- a/unittest/commands/test_lattice_region.cpp
+++ b/unittest/commands/test_lattice_region.cpp
@@ -45,7 +45,9 @@ protected:
     {
         testbinary = "LatticeRegionTest";
         LAMMPSTest::SetUp();
-        command("units metal");
+        HIDE_OUTPUT([&] {
+            command("units metal");
+        });
     }
 };
 
@@ -63,7 +65,7 @@ TEST_F(LatticeRegionTest, lattice_none)
     ASSERT_EQ(lattice->basis, nullptr);
 
     TEST_FAILURE(".*ERROR: Illegal lattice command.*", command("lattice"););
-    TEST_FAILURE(".*ERROR: Illegal lattice command.*", command("lattice xxx"););
+    TEST_FAILURE(".*ERROR: Unknown lattice keyword: xxx.*", command("lattice xxx"););
     TEST_FAILURE(".*ERROR: Illegal lattice command.*", command("lattice none 1.0 origin"););
     TEST_FAILURE(".*ERROR: Expected floating point.*", command("lattice none xxx"););
 
@@ -114,10 +116,11 @@ TEST_F(LatticeRegionTest, lattice_sc)
     ASSERT_EQ(lattice->basis[0][1], 0.0);
     ASSERT_EQ(lattice->basis[0][2], 0.0);
 
-    TEST_FAILURE(".*ERROR: Illegal lattice command.*",
+    TEST_FAILURE(".*ERROR: Invalid lattice origin argument: 1.*",
                  command("lattice sc 1.0 origin 1.0 1.0 1.0"););
-    TEST_FAILURE(".*ERROR: Illegal lattice command.*", command("lattice sc 1.0 origin 1.0"););
-    TEST_FAILURE(".*ERROR: Illegal lattice command.*",
+    TEST_FAILURE(".*ERROR: Illegal lattice origin command: missing argument.*",
+                 command("lattice sc 1.0 origin 1.0"););
+    TEST_FAILURE(".*ERROR: Unknown lattice keyword: xxx.*",
                  command("lattice sc 1.0 origin 0.0 0.0 0.0 xxx"););
     TEST_FAILURE(".*ERROR: Expected floating point.*",
                  command("lattice sc 1.0 origin xxx 1.0 1.0"););
@@ -195,11 +198,12 @@ TEST_F(LatticeRegionTest, lattice_fcc)
     ASSERT_EQ(lattice->basis[3][1], 0.5);
     ASSERT_EQ(lattice->basis[3][2], 0.5);
 
-    TEST_FAILURE(".*ERROR: Invalid option in lattice command for non-custom style.*",
+    TEST_FAILURE(".*ERROR: Invalid basis option in lattice command for non-custom style.*",
                  command("lattice fcc 1.0 basis 0.0 0.0 0.0"););
-    TEST_FAILURE(".*ERROR: Invalid option in lattice command for non-custom style.*",
+    TEST_FAILURE(".*ERROR: Invalid a1 option in lattice command for non-custom style.*",
                  command("lattice fcc 1.0 a1 0.0 1.0 0.0"););
-    TEST_FAILURE(".*ERROR: Illegal lattice command.*", command("lattice fcc 1.0 orient w 1 0 0"););
+    TEST_FAILURE(".*ERROR: Unknown lattice orient argument: w.*",
+                 command("lattice fcc 1.0 orient w 1 0 0"););
 
     BEGIN_HIDE_OUTPUT();
     command("dimension 2");
@@ -241,9 +245,9 @@ TEST_F(LatticeRegionTest, lattice_hcp)
     ASSERT_EQ(lattice->a3[1], 0.0);
     ASSERT_DOUBLE_EQ(lattice->a3[2], sqrt(8.0 / 3.0));
 
-    TEST_FAILURE(".*ERROR: Invalid option in lattice command for non-custom style.*",
+    TEST_FAILURE(".*ERROR: Invalid a2 option in lattice command for non-custom style.*",
                  command("lattice hcp 1.0 a2 0.0 1.0 0.0"););
-    TEST_FAILURE(".*ERROR: Invalid option in lattice command for non-custom style.*",
+    TEST_FAILURE(".*ERROR: Invalid a3 option in lattice command for non-custom style.*",
                  command("lattice hcp 1.0 a3 0.0 1.0 0.0"););
     BEGIN_HIDE_OUTPUT();
     command("dimension 2");
@@ -452,9 +456,9 @@ TEST_F(LatticeRegionTest, lattice_custom)
     ASSERT_DOUBLE_EQ(lattice->a3[1], 0.0);
     ASSERT_DOUBLE_EQ(lattice->a3[2], 4.34 * sqrt(8.0 / 3.0));
 
-    TEST_FAILURE(".*ERROR: Illegal lattice command.*",
+    TEST_FAILURE(".*ERROR: Invalid lattice basis argument: -0.1.*",
                  command("lattice custom 1.0 basis -0.1 0 0"););
-    TEST_FAILURE(".*ERROR: Illegal lattice command.*",
+    TEST_FAILURE(".*ERROR: Invalid lattice basis argument: 1.*",
                  command("lattice custom 1.0 basis 0.0 1.0 0"););
 
     BEGIN_HIDE_OUTPUT();

From ff9c02f0535a57d0659d314ac058d180b55e246f Mon Sep 17 00:00:00 2001
From: Jiancheng Chen <2742581175@qq.com>
Date: Thu, 18 Aug 2022 21:08:36 +0800
Subject: [PATCH 3/8] improved error messages in pair and input.cpp

---
 src/domain.cpp   |  2 +-
 src/input.cpp    | 46 +++++++++++++++++++++++-----------------------
 src/lattice.cpp  |  2 +-
 src/neighbor.cpp |  2 +-
 src/pair.cpp     | 24 ++++++++++++------------
 5 files changed, 38 insertions(+), 38 deletions(-)

diff --git a/src/domain.cpp b/src/domain.cpp
index 7d60c20a24..d3d6985f99 100644
--- a/src/domain.cpp
+++ b/src/domain.cpp
@@ -1856,7 +1856,7 @@ const std::vector<Region *> Domain::get_region_list()
 
 void Domain::set_boundary(int narg, char **arg, int flag)
 {
-  if (narg != 3) error->all(FLERR,"Illegal boundary command: expected 3 argument but found {}", narg);
+  if (narg != 3) error->all(FLERR,"Illegal boundary command: expected 3 arguments but found {}", narg);
 
   char c;
   for (int idim = 0; idim < 3; idim++)
diff --git a/src/input.cpp b/src/input.cpp
index bb84a86e2c..f11cb5177b 100644
--- a/src/input.cpp
+++ b/src/input.cpp
@@ -860,7 +860,7 @@ int Input::execute_command()
 
 void Input::clear()
 {
-  if (narg > 0) error->all(FLERR,"Illegal clear command");
+  if (narg > 0) error->all(FLERR,"Illegal clear command: unexpected arguments but found {}", narg);
   lmp->destroy();
   lmp->create();
   lmp->post_create();
@@ -870,7 +870,7 @@ void Input::clear()
 
 void Input::echo()
 {
-  if (narg != 1) error->all(FLERR,"Illegal echo command");
+  if (narg != 1) error->all(FLERR,"Illegal echo command: expected 1 argument but found {}", narg);
 
   if (strcmp(arg[0],"none") == 0) {
     echo_screen = 0;
@@ -884,14 +884,14 @@ void Input::echo()
   } else if (strcmp(arg[0],"both") == 0) {
     echo_screen = 1;
     echo_log = 1;
-  } else error->all(FLERR,"Illegal echo command");
+  } else error->all(FLERR,"Unknown echo keyword: {}", arg[0]);
 }
 
 /* ---------------------------------------------------------------------- */
 
 void Input::ifthenelse()
 {
-  if (narg < 3) error->all(FLERR,"Illegal if command");
+  if (narg < 3) utils::missing_cmd_args(FLERR, "if", error);
 
   // substitute for variables in Boolean expression for "if"
   // in case expression was enclosed in quotes
@@ -908,7 +908,7 @@ void Input::ifthenelse()
 
   // bound "then" commands
 
-  if (strcmp(arg[1],"then") != 0) error->all(FLERR,"Illegal if command");
+  if (strcmp(arg[1],"then") != 0) error->all(FLERR,"Illegal if command: expected \"then\" but found \"{}\"", arg[1]);
 
   int first = 2;
   int iarg = first;
@@ -923,13 +923,13 @@ void Input::ifthenelse()
 
   if (btest != 0.0) {
     int ncommands = last-first + 1;
-    if (ncommands <= 0) error->all(FLERR,"Illegal if command");
+    if (ncommands <= 0) utils::missing_cmd_args(FLERR, "if then", error);
 
     auto commands = new char*[ncommands];
     ncommands = 0;
     for (int i = first; i <= last; i++) {
       n = strlen(arg[i]) + 1;
-      if (n == 1) error->all(FLERR,"Illegal if command");
+      if (n == 1) error->all(FLERR,"Illegal if then command: execute command is empty");
       commands[ncommands] = new char[n];
       strcpy(commands[ncommands],arg[i]);
       ncommands++;
@@ -954,7 +954,7 @@ void Input::ifthenelse()
   // bound and execute "elif" or "else" commands
 
   while (iarg != narg) {
-    if (iarg+2 > narg) error->all(FLERR,"Illegal if command");
+    if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "if then", error);
     if (strcmp(arg[iarg],"elif") == 0) {
       n = strlen(arg[iarg+1]) + 1;
       if (n > maxline) reallocate(line,maxline,n);
@@ -976,13 +976,13 @@ void Input::ifthenelse()
     if (btest == 0.0) continue;
 
     int ncommands = last-first + 1;
-    if (ncommands <= 0) error->all(FLERR,"Illegal if command");
+    if (ncommands <= 0) utils::missing_cmd_args(FLERR, "if elif/else", error);
 
     auto commands = new char*[ncommands];
     ncommands = 0;
     for (int i = first; i <= last; i++) {
       n = strlen(arg[i]) + 1;
-      if (n == 1) error->all(FLERR,"Illegal if command");
+      if (n == 1) error->all(FLERR,"Illegal if elif/else command: execute command is empty");
       commands[ncommands] = new char[n];
       strcpy(commands[ncommands],arg[i]);
       ncommands++;
@@ -1038,7 +1038,7 @@ void Input::include()
 
 void Input::jump()
 {
-  if (narg < 1 || narg > 2) error->all(FLERR,"Illegal jump command");
+  if (narg < 1 || narg > 2) error->all(FLERR,"Illegal jump command: expected 1 or 2 argument(s) but found {}", narg);
 
   if (jump_skip) {
     jump_skip = 0;
@@ -1069,7 +1069,7 @@ void Input::jump()
 
 void Input::label()
 {
-  if (narg != 1) error->all(FLERR,"Illegal label command");
+  if (narg != 1) error->all(FLERR,"Illegal label command: expected 1 argument but found {}", narg);
   if (label_active && strcmp(labelstr,arg[0]) == 0) label_active = 0;
 }
 
@@ -1077,12 +1077,12 @@ void Input::label()
 
 void Input::log()
 {
-  if ((narg < 1) || (narg > 2)) error->all(FLERR,"Illegal log command");
+  if ((narg < 1) || (narg > 2)) error->all(FLERR,"Illegal log command: expected 1 or 2 argument(s) but found {}", narg);
 
   int appendflag = 0;
   if (narg == 2) {
     if (strcmp(arg[1],"append") == 0) appendflag = 1;
-    else error->all(FLERR,"Illegal log command");
+    else error->all(FLERR,"Unknown log keyword: {}", arg[1]);
   }
 
   if (me == 0) {
@@ -1112,7 +1112,7 @@ void Input::next_command()
 
 void Input::partition()
 {
-  if (narg < 3) error->all(FLERR,"Illegal partition command");
+  if (narg < 3) utils::missing_cmd_args(FLERR, "partition", error);
 
   int ilo,ihi;
   int yesflag = utils::logical(FLERR,arg[0],false,lmp);
@@ -1138,7 +1138,7 @@ void Input::partition()
 
 void Input::print()
 {
-  if (narg < 1) error->all(FLERR,"Illegal print command");
+  if (narg < 1) utils::missing_cmd_args(FLERR, "print", error);
 
   // copy 1st arg back into line (copy is being used)
   // check maxline since arg[0] could have been expanded by variables
@@ -1158,7 +1158,7 @@ void Input::print()
   int iarg = 1;
   while (iarg < narg) {
     if (strcmp(arg[iarg],"file") == 0 || strcmp(arg[iarg],"append") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal print command");
+      if (iarg+2 > narg) error->all(FLERR,"Illegal print {} command: missing argument(s)", arg[iarg]);
       if (me == 0) {
         if (fp != nullptr) fclose(fp);
         if (strcmp(arg[iarg],"file") == 0) fp = fopen(arg[iarg+1],"w");
@@ -1168,14 +1168,14 @@ void Input::print()
       }
       iarg += 2;
     } else if (strcmp(arg[iarg],"screen") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal print command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "print screen", error);
       screenflag = utils::logical(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg],"universe") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal print command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "print universe", error);
       universeflag = utils::logical(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
-    } else error->all(FLERR,"Illegal print command");
+    } else error->all(FLERR,"Unknown print keyword: {}", arg[iarg]);
   }
 
   if (me == 0) {
@@ -1205,7 +1205,7 @@ void Input::quit()
 {
   if (narg == 0) error->done(0); // 1 would be fully backwards compatible
   if (narg == 1) error->done(utils::inumeric(FLERR,arg[0],false,lmp));
-  error->all(FLERR,"Illegal quit command");
+  error->all(FLERR,"Illegal quit command: expected 0 or 1 argument but found {}", narg);
 }
 
 /* ---------------------------------------------------------------------- */
@@ -1589,7 +1589,7 @@ void Input::lattice()
 
 void Input::mass()
 {
-  if (narg != 2) error->all(FLERR,"Illegal mass command");
+  if (narg != 2) error->all(FLERR,"Illegal mass command: expected 2 arguments but found {}", narg);
   if (domain->box_exist == 0)
     error->all(FLERR,"Mass command before simulation box is defined");
   atom->set_mass(FLERR,narg,arg);
@@ -1731,7 +1731,7 @@ void Input::pair_modify()
 
 void Input::pair_style()
 {
-  if (narg < 1) error->all(FLERR,"Illegal pair_style command");
+  if (narg < 1) utils::missing_cmd_args(FLERR, "pair_style", error);
   if (force->pair) {
     std::string style = arg[0];
     int match = 0;
diff --git a/src/lattice.cpp b/src/lattice.cpp
index f88a55a4d5..8ba74d52d6 100644
--- a/src/lattice.cpp
+++ b/src/lattice.cpp
@@ -51,7 +51,7 @@ Lattice::Lattice(LAMMPS *lmp, int narg, char **arg) : Pointers(lmp)
   else error->all(FLERR,"Unknown lattice keyword: {}", arg[0]);
 
   if (style == NONE) {
-    if (narg != 2) error->all(FLERR,"Illegal lattice command: expected 2 argument but found {}", narg);
+    if (narg != 2) error->all(FLERR,"Illegal lattice command: expected 2 arguments but found {}", narg);
 
     // Domain creates a default lattice of style "none"
     //   before Force class is instantiated, just use atof() in that case
diff --git a/src/neighbor.cpp b/src/neighbor.cpp
index ec97f4dced..e5e378ff6b 100644
--- a/src/neighbor.cpp
+++ b/src/neighbor.cpp
@@ -2527,7 +2527,7 @@ void Neighbor::build_one(class NeighList *mylist, int preflag)
 
 void Neighbor::set(int narg, char **arg)
 {
-  if (narg != 2) error->all(FLERR,"Illegal neighbor command: expected 2 argument but found {}", narg);
+  if (narg != 2) error->all(FLERR,"Illegal neighbor command: expected 2 arguments but found {}", narg);
 
   skin = utils::numeric(FLERR,arg[0],false,lmp);
   if (skin < 0.0) error->all(FLERR, "Invalid neighbor argument: {}", arg[0]);
diff --git a/src/pair.cpp b/src/pair.cpp
index 4d42035fd1..81f231bb31 100644
--- a/src/pair.cpp
+++ b/src/pair.cpp
@@ -159,57 +159,57 @@ Pair::~Pair()
 
 void Pair::modify_params(int narg, char **arg)
 {
-  if (narg == 0) error->all(FLERR,"Illegal pair_modify command");
+  if (narg == 0) utils::missing_cmd_args(FLERR, "pair_modify", error);
 
   int iarg = 0;
   while (iarg < narg) {
     if (strcmp(arg[iarg],"mix") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal pair_modify command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "pair_modify mix", error);
       if (strcmp(arg[iarg+1],"geometric") == 0) mix_flag = GEOMETRIC;
       else if (strcmp(arg[iarg+1],"arithmetic") == 0) mix_flag = ARITHMETIC;
       else if (strcmp(arg[iarg+1],"sixthpower") == 0) mix_flag = SIXTHPOWER;
-      else error->all(FLERR,"Illegal pair_modify command");
+      else error->all(FLERR,"Unknown pair_modify mix argument: {}", arg[iarg+1]);
       iarg += 2;
     } else if (strcmp(arg[iarg],"shift") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal pair_modify command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "pair_modify shift", error);
       offset_flag = utils::logical(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg],"table") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal pair_modify command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "pair_modify table", error);
       ncoultablebits = utils::inumeric(FLERR,arg[iarg+1],false,lmp);
       if (ncoultablebits > (int)sizeof(float)*CHAR_BIT)
         error->all(FLERR,"Too many total bits for bitmapped lookup table");
       iarg += 2;
     } else if (strcmp(arg[iarg],"table/disp") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal pair_modify command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "pair_modify table/disp", error);
       ndisptablebits = utils::inumeric(FLERR,arg[iarg+1],false,lmp);
       if (ndisptablebits > (int)sizeof(float)*CHAR_BIT)
         error->all(FLERR,"Too many total bits for bitmapped lookup table");
       iarg += 2;
     } else if (strcmp(arg[iarg],"tabinner") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal pair_modify command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "pair_modify tabinner", error);
       tabinner = utils::numeric(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg],"tabinner/disp") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal pair_modify command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "pair_modify tabinner/disp", error);
       tabinner_disp = utils::numeric(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg],"tail") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal pair_modify command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "pair_modify tail", error);
       tail_flag = utils::logical(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg],"compute") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal pair_modify command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "pair_modify compute", error);
       compute_flag = utils::logical(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg],"nofdotr") == 0) {
       no_virial_fdotr_compute = 1;
       ++iarg;
     } else if (strcmp(arg[iarg],"neigh/trim") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal pair_modify command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "pair_modify neigh/trim", error);
       trim_flag = utils::logical(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
-    } else error->all(FLERR,"Illegal pair_modify command");
+    } else error->all(FLERR,"Unknown pair_modify keyword: {}", arg[iarg]);
   }
 }
 

From 9edb1ee928976ba7fabe5400dd233570b085563c Mon Sep 17 00:00:00 2001
From: Jiancheng Chen <2742581175@qq.com>
Date: Thu, 18 Aug 2022 21:14:39 +0800
Subject: [PATCH 4/8] improved error messages in input.cpp

---
 src/input.cpp | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/src/input.cpp b/src/input.cpp
index f11cb5177b..ef125d3145 100644
--- a/src/input.cpp
+++ b/src/input.cpp
@@ -1214,10 +1214,10 @@ void Input::shell()
 {
   int rv,err;
 
-  if (narg < 1) error->all(FLERR,"Illegal shell command");
+  if (narg < 1) utils::missing_cmd_args(FLERR, "shell", error);
 
   if (strcmp(arg[0],"cd") == 0) {
-    if (narg != 2) error->all(FLERR,"Illegal shell cd command");
+    if (narg != 2) error->all(FLERR,"Illegal shell command: expected 2 argument but found {}", narg);
     rv = (platform::chdir(arg[1]) < 0) ? errno : 0;
     MPI_Reduce(&rv,&err,1,MPI_INT,MPI_MAX,0,world);
     errno = err;
@@ -1225,7 +1225,7 @@ void Input::shell()
       error->warning(FLERR, "Shell command 'cd {}' failed with error '{}'", arg[1], utils::getsyserror());
     }
   } else if (strcmp(arg[0],"mkdir") == 0) {
-    if (narg < 2) error->all(FLERR,"Illegal shell mkdir command");
+    if (narg < 2) utils::missing_cmd_args(FLERR, "shell mkdir", error);
     if (me == 0) {
       for (int i = 1; i < narg; i++) {
         rv = (platform::mkdir(arg[i]) < 0) ? errno : 0;
@@ -1235,7 +1235,7 @@ void Input::shell()
       }
     }
   } else if (strcmp(arg[0],"mv") == 0) {
-    if (narg != 3) error->all(FLERR,"Illegal shell mv command");
+    if (narg != 3) error->all(FLERR,"Illegal shell command: expected 3 argument but found {}", narg);
     if (me == 0) {
       if (platform::path_is_directory(arg[2])) {
         if (system(fmt::format("mv {} {}", arg[1], arg[2]).c_str()))
@@ -1248,7 +1248,7 @@ void Input::shell()
       }
     }
   } else if (strcmp(arg[0],"rm") == 0) {
-    if (narg < 2) error->all(FLERR,"Illegal shell rm command");
+    if (narg < 2) utils::missing_cmd_args(FLERR, "shell rm", error);
     if (me == 0) {
       int i = 1;
       bool warn = true;
@@ -1264,7 +1264,7 @@ void Input::shell()
       }
     }
   } else if (strcmp(arg[0],"rmdir") == 0) {
-    if (narg < 2) error->all(FLERR,"Illegal shell rmdir command");
+    if (narg < 2) utils::missing_cmd_args(FLERR, "shell rmdir", error);
     if (me == 0) {
       for (int i = 1; i < narg; i++) {
         if (platform::rmdir(arg[i]) < 0)
@@ -1273,7 +1273,7 @@ void Input::shell()
       }
     }
   } else if (strcmp(arg[0],"putenv") == 0) {
-    if (narg < 2) error->all(FLERR,"Illegal shell putenv command");
+    if (narg < 2) utils::missing_cmd_args(FLERR, "shell putenv", error);
     for (int i = 1; i < narg; i++) {
       rv = 0;
       if (arg[i]) rv = platform::putenv(arg[i]);

From 414b0b14756b8848f8d981542236c53c04d87e7d Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Thu, 18 Aug 2022 10:52:25 -0400
Subject: [PATCH 5/8] update unit tests

---
 unittest/commands/test_simple_commands.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/unittest/commands/test_simple_commands.cpp b/unittest/commands/test_simple_commands.cpp
index c58efcd9ea..2563c09848 100644
--- a/unittest/commands/test_simple_commands.cpp
+++ b/unittest/commands/test_simple_commands.cpp
@@ -81,7 +81,7 @@ TEST_F(SimpleCommandsTest, Echo)
     ASSERT_EQ(lmp->input->echo_log, 1);
 
     TEST_FAILURE(".*ERROR: Illegal echo command.*", command("echo"););
-    TEST_FAILURE(".*ERROR: Illegal echo command.*", command("echo xxx"););
+    TEST_FAILURE(".*ERROR: Unknown echo keyword: xxx.*", command("echo xxx"););
 }
 
 TEST_F(SimpleCommandsTest, Log)

From 3ec06dd2c25418ca0afd9f243599ff91a7d2575e Mon Sep 17 00:00:00 2001
From: Jiancheng Chen <2742581175@qq.com>
Date: Fri, 19 Aug 2022 21:06:00 +0800
Subject: [PATCH 6/8] improve some error messages in comm, domain and
 region.cpp

---
 src/comm.cpp   | 32 ++++++++++++++++----------------
 src/domain.cpp | 10 +++++-----
 src/region.cpp | 16 ++++++++--------
 3 files changed, 29 insertions(+), 29 deletions(-)

diff --git a/src/comm.cpp b/src/comm.cpp
index 5175af28e5..1679cc3c41 100644
--- a/src/comm.cpp
+++ b/src/comm.cpp
@@ -282,12 +282,12 @@ void Comm::init_exchange()
 
 void Comm::modify_params(int narg, char **arg)
 {
-  if (narg < 1) error->all(FLERR,"Illegal comm_modify command");
+  if (narg < 1) utils::missing_cmd_args(FLERR, "comm_modify", error);
 
   int iarg = 0;
   while (iarg < narg) {
     if (strcmp(arg[iarg],"mode") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal comm_modify command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "comm_modify mode", error);
       if (strcmp(arg[iarg+1],"single") == 0) {
         // need to reset cutghostuser when switching comm mode
         if (mode == Comm::MULTI) cutghostuser = 0.0;
@@ -311,26 +311,27 @@ void Comm::modify_params(int narg, char **arg)
         if (mode == Comm::MULTI) cutghostuser = 0.0;
         memory->destroy(cutusermulti);
         mode = Comm::MULTIOLD;
-      } else error->all(FLERR,"Illegal comm_modify command");
+      } else error->all(FLERR,"Unknown comm_modify mode argument: {}", arg[iarg+1]);
       iarg += 2;
     } else if (strcmp(arg[iarg],"group") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal comm_modify command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "comm_modify group", error);
       bordergroup = group->find(arg[iarg+1]);
       if (bordergroup < 0)
-        error->all(FLERR,"Invalid group in comm_modify command");
-      if (bordergroup && (atom->firstgroupname == nullptr ||
-                          strcmp(arg[iarg+1],atom->firstgroupname) != 0))
-        error->all(FLERR,"Comm_modify group != atom_modify first group");
+        error->all(FLERR, "Invalid comm_modify keyword: group {} not found", arg[iarg+1]);
+      if (atom->firstgroupname == nullptr)
+        error->all(FLERR, "Invalid comm_modify keyword: atom_modify first command must be used");
+      if (strcmp(arg[iarg+1],atom->firstgroupname) != 0)
+        error->all(FLERR, "comm_modify group != atom_modify first group: {}", atom->firstgroupname);
       iarg += 2;
     } else if (strcmp(arg[iarg],"cutoff") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal comm_modify command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "comm_modify cutoff", error);
       if (mode == Comm::MULTI)
         error->all(FLERR, "Use cutoff/multi keyword to set cutoff in multi mode");
       if (mode == Comm::MULTIOLD)
         error->all(FLERR, "Use cutoff/multi/old keyword to set cutoff in multi mode");
       cutghostuser = utils::numeric(FLERR,arg[iarg+1],false,lmp);
       if (cutghostuser < 0.0)
-        error->all(FLERR,"Invalid cutoff in comm_modify command");
+        error->all(FLERR,"Invalid cutoff {} in comm_modify command", arg[iarg+1]);
       iarg += 2;
     } else if (strcmp(arg[iarg],"cutoff/multi") == 0) {
       int i,nlo,nhi;
@@ -355,7 +356,7 @@ void Comm::modify_params(int narg, char **arg)
       cut = utils::numeric(FLERR,arg[iarg+2],false,lmp);
       cutghostuser = MAX(cutghostuser,cut);
       if (cut < 0.0)
-        error->all(FLERR,"Invalid cutoff in comm_modify command");
+        error->all(FLERR,"Invalid cutoff {} in comm_modify command", arg[iarg+2]);
       // collections use 1-based indexing externally and 0-based indexing internally
       for (i=nlo; i<=nhi; ++i)
         cutusermulti[i-1] = cut;
@@ -370,8 +371,7 @@ void Comm::modify_params(int narg, char **arg)
       if (domain->box_exist == 0)
         error->all(FLERR, "Cannot set cutoff/multi before simulation box is defined");
       const int ntypes = atom->ntypes;
-      if (iarg+3 > narg)
-        error->all(FLERR,"Illegal comm_modify command");
+      if (iarg+3 > narg) utils::missing_cmd_args(FLERR, "comm_modify cutoff/multi/old", error);
       if (cutusermultiold == nullptr) {
         memory->create(cutusermultiold,ntypes+1,"comm:cutusermultiold");
         for (i=0; i < ntypes+1; ++i)
@@ -381,7 +381,7 @@ void Comm::modify_params(int narg, char **arg)
       cut = utils::numeric(FLERR,arg[iarg+2],false,lmp);
       cutghostuser = MAX(cutghostuser,cut);
       if (cut < 0.0)
-        error->all(FLERR,"Invalid cutoff in comm_modify command");
+        error->all(FLERR,"Invalid cutoff {} in comm_modify command", arg[iarg+2]);
       for (i=nlo; i<=nhi; ++i)
         cutusermultiold[i] = cut;
       iarg += 3;
@@ -391,10 +391,10 @@ void Comm::modify_params(int narg, char **arg)
       multi_reduce = 1;
       iarg += 1;
     } else if (strcmp(arg[iarg],"vel") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal comm_modify command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "comm_modify vel", error);
       ghost_velocity = utils::logical(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
-    } else error->all(FLERR,"Illegal comm_modify command");
+    } else error->all(FLERR,"Unknown comm_modify keyword: {}", arg[iarg]);
   }
 }
 
diff --git a/src/domain.cpp b/src/domain.cpp
index d3d6985f99..4d299fb7bf 100644
--- a/src/domain.cpp
+++ b/src/domain.cpp
@@ -1744,7 +1744,7 @@ void Domain::set_lattice(int narg, char **arg)
 
 void Domain::add_region(int narg, char **arg)
 {
-  if (narg < 2) error->all(FLERR,"Illegal region command");
+  if (narg < 2) utils::missing_cmd_args(FLERR, "region", error);
 
   if (strcmp(arg[1],"delete") == 0) {
     delete_region(arg[0]);
@@ -1935,17 +1935,17 @@ void Domain::set_boundary(int narg, char **arg, int flag)
 
 void Domain::set_box(int narg, char **arg)
 {
-  if (narg < 1) error->all(FLERR,"Illegal box command");
+  if (narg < 1) utils::missing_cmd_args(FLERR, "box", error);
 
   int iarg = 0;
   while (iarg < narg) {
     if (strcmp(arg[iarg],"tilt") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal box command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "box tilt", error);
       if (strcmp(arg[iarg+1],"small") == 0) tiltsmall = 1;
       else if (strcmp(arg[iarg+1],"large") == 0) tiltsmall = 0;
-      else error->all(FLERR,"Illegal box command");
+      else error->all(FLERR,"Unknown box tilt argument: {}", arg[iarg+1]);
       iarg += 2;
-    } else error->all(FLERR,"Illegal box command");
+    } else error->all(FLERR,"Unknown box keyword: {}", arg[iarg]);
   }
 }
 
diff --git a/src/region.cpp b/src/region.cpp
index 307513add6..d63fe25017 100644
--- a/src/region.cpp
+++ b/src/region.cpp
@@ -66,27 +66,27 @@ void Region::init()
 {
   if (xstr) {
     xvar = input->variable->find(xstr);
-    if (xvar < 0) error->all(FLERR, "Variable name for region does not exist");
+    if (xvar < 0) error->all(FLERR, "Variable {} for region does not exist", xstr);
     if (!input->variable->equalstyle(xvar))
-      error->all(FLERR, "Variable for region is invalid style");
+      error->all(FLERR, "Variable {} for region is invalid style", xstr);
   }
   if (ystr) {
     yvar = input->variable->find(ystr);
-    if (yvar < 0) error->all(FLERR, "Variable name for region does not exist");
+    if (yvar < 0) error->all(FLERR, "Variable {} for region does not exist", ystr);
     if (!input->variable->equalstyle(yvar))
-      error->all(FLERR, "Variable for region is not equal style");
+      error->all(FLERR, "Variable {} for region is not equal style", ystr);
   }
   if (zstr) {
     zvar = input->variable->find(zstr);
-    if (zvar < 0) error->all(FLERR, "Variable name for region does not exist");
+    if (zvar < 0) error->all(FLERR, "Variable {} for region does not exist", zstr);
     if (!input->variable->equalstyle(zvar))
-      error->all(FLERR, "Variable for region is not equal style");
+      error->all(FLERR, "Variable {} for region is not equal style", zstr);
   }
   if (tstr) {
     tvar = input->variable->find(tstr);
-    if (tvar < 0) error->all(FLERR, "Variable name for region does not exist");
+    if (tvar < 0) error->all(FLERR, "Variable {} for region does not exist", tstr);
     if (!input->variable->equalstyle(tvar))
-      error->all(FLERR, "Variable for region is not equal style");
+      error->all(FLERR, "Variable {} for region is not equal style", tstr);
   }
   vel_timestep = -1;
 }

From 59837dd44bf8b716d10fb154beaa96909146cf3a Mon Sep 17 00:00:00 2001
From: Jiancheng Chen <2742581175@qq.com>
Date: Thu, 25 Aug 2022 11:09:21 +0800
Subject: [PATCH 7/8] improve error messages in run and variable.cpp

---
 src/run.cpp      | 26 +++++++++++++-------------
 src/variable.cpp | 47 +++++++++++++++++++++++++----------------------
 2 files changed, 38 insertions(+), 35 deletions(-)

diff --git a/src/run.cpp b/src/run.cpp
index a026580c83..3a9a4dc32e 100644
--- a/src/run.cpp
+++ b/src/run.cpp
@@ -36,7 +36,7 @@ Run::Run(LAMMPS *lmp) : Command(lmp) {}
 
 void Run::command(int narg, char **arg)
 {
-  if (narg < 1) error->all(FLERR,"Illegal run command");
+  if (narg < 1) utils::missing_cmd_args(FLERR, "run", error);
 
   if (domain->box_exist == 0)
     error->all(FLERR,"Run command before simulation box is defined");
@@ -62,25 +62,25 @@ void Run::command(int narg, char **arg)
   int iarg = 1;
   while (iarg < narg) {
     if (strcmp(arg[iarg],"upto") == 0) {
-      if (iarg+1 > narg) error->all(FLERR,"Illegal run command");
+      if (iarg+1 > narg) utils::missing_cmd_args(FLERR, "run upto", error);
       uptoflag = 1;
       iarg += 1;
     } else if (strcmp(arg[iarg],"start") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal run command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "run start", error);
       startflag = 1;
       start = utils::bnumeric(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg],"stop") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal run command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "run stop", error);
       stopflag = 1;
       stop = utils::bnumeric(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg],"pre") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal run command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "run pre", error);
       preflag = utils::logical(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
     } else if (strcmp(arg[iarg],"post") == 0) {
-      if (iarg+2 > narg) error->all(FLERR,"Illegal run command");
+      if (iarg+2 > narg) utils::missing_cmd_args(FLERR, "run post", error);
       postflag = utils::logical(FLERR,arg[iarg+1],false,lmp);
       iarg += 2;
 
@@ -89,15 +89,15 @@ void Run::command(int narg, char **arg)
       // set ncommands = 0 if single command and it is "NULL"
 
     } else if (strcmp(arg[iarg],"every") == 0) {
-      if (iarg+3 > narg) error->all(FLERR,"Illegal run command");
+      if (iarg+3 > narg) utils::missing_cmd_args(FLERR, "run every", error);
       nevery = utils::inumeric(FLERR,arg[iarg+1],false,lmp);
-      if (nevery <= 0) error->all(FLERR,"Illegal run command");
+      if (nevery <= 0) error->all(FLERR, "Invalid run every argument: {}", nevery);
       first = iarg+2;
       last = narg-1;
       ncommands = last-first + 1;
       if (ncommands == 1 && strcmp(arg[first],"NULL") == 0) ncommands = 0;
       iarg = narg;
-    } else error->all(FLERR,"Illegal run command");
+    } else error->all(FLERR,"Unknown run keyword: {}", arg[iarg]);
   }
 
   // set nsteps as integer, using upto value if specified
@@ -105,12 +105,12 @@ void Run::command(int narg, char **arg)
   int nsteps;
   if (!uptoflag) {
     if (nsteps_input < 0 || nsteps_input > MAXSMALLINT)
-      error->all(FLERR,"Invalid run command N value");
+      error->all(FLERR,"Invalid run command N value: {}", nsteps_input);
     nsteps = static_cast<int> (nsteps_input);
   } else {
     bigint delta = nsteps_input - update->ntimestep;
     if (delta < 0 || delta > MAXSMALLINT)
-      error->all(FLERR,"Invalid run command upto value");
+      error->all(FLERR,"Invalid run command upto value: {}", delta);
     nsteps = static_cast<int> (delta);
   }
 
@@ -118,13 +118,13 @@ void Run::command(int narg, char **arg)
 
   if (startflag) {
     if (start < 0)
-      error->all(FLERR,"Invalid run command start/stop value");
+      error->all(FLERR,"Invalid run command start value: {}", start);
     if (start > update->ntimestep)
       error->all(FLERR,"Run command start value is after start of run");
   }
   if (stopflag) {
     if (stop < 0)
-      error->all(FLERR,"Invalid run command start/stop value");
+      error->all(FLERR,"Invalid run command stop value: {}", stop);
     if (stop < update->ntimestep + nsteps)
       error->all(FLERR,"Run command stop value is before end of run");
   }
diff --git a/src/variable.cpp b/src/variable.cpp
index a564847b68..d6eec9eeb3 100644
--- a/src/variable.cpp
+++ b/src/variable.cpp
@@ -162,7 +162,7 @@ Variable::~Variable()
 
 void Variable::set(int narg, char **arg)
 {
-  if (narg < 2) error->all(FLERR,"Illegal variable command");
+  if (narg < 2) utils::missing_cmd_args(FLERR, "variable", error);
 
   int replaceflag = 0;
 
@@ -170,7 +170,7 @@ void Variable::set(int narg, char **arg)
   // doesn't matter if variable no longer exists
 
   if (strcmp(arg[1],"delete") == 0) {
-    if (narg != 2) error->all(FLERR,"Illegal variable command");
+    if (narg != 2) error->all(FLERR,"Illegal variable command: expected 2 argument but found {}", narg);
     if (find(arg[0]) >= 0) remove(find(arg[0]));
     return;
 
@@ -178,7 +178,7 @@ void Variable::set(int narg, char **arg)
   // num = listed args, which = 1st value, data = copied args
 
   } else if (strcmp(arg[1],"index") == 0) {
-    if (narg < 3) error->all(FLERR,"Illegal variable command");
+    if (narg < 3) utils::missing_cmd_args(FLERR, "variable index", error);
     if (find(arg[0]) >= 0) return;
     if (nvar == maxvar) grow();
     style[nvar] = INDEX;
@@ -193,6 +193,7 @@ void Variable::set(int narg, char **arg)
   // 2 args + pad: num = N2, which = N1, data = single string
 
   } else if (strcmp(arg[1],"loop") == 0) {
+    if (narg < 3) utils::missing_cmd_args(FLERR, "variable loop", error);
     if (find(arg[0]) >= 0) return;
     if (nvar == maxvar) grow();
     style[nvar] = LOOP;
@@ -200,7 +201,7 @@ void Variable::set(int narg, char **arg)
     if (narg == 3 || (narg == 4 && strcmp(arg[3],"pad") == 0)) {
       nfirst = 1;
       nlast = utils::inumeric(FLERR,arg[2],false,lmp);
-      if (nlast <= 0) error->all(FLERR,"Illegal variable command");
+      if (nlast <= 0) error->all(FLERR, "Invalid variable loop argument: {}", nlast);
       if (narg == 4 && strcmp(arg[3],"pad") == 0) {
         pad[nvar] = fmt::format("{}",nlast).size();
       } else pad[nvar] = 0;
@@ -208,11 +209,11 @@ void Variable::set(int narg, char **arg)
       nfirst = utils::inumeric(FLERR,arg[2],false,lmp);
       nlast = utils::inumeric(FLERR,arg[3],false,lmp);
       if (nfirst > nlast || nlast < 0)
-        error->all(FLERR,"Illegal variable command");
+        error->all(FLERR,"Illegal variable loop command: {} > {}", nfirst,nlast);
       if (narg == 5 && strcmp(arg[4],"pad") == 0) {
         pad[nvar] = fmt::format("{}",nlast).size();
       } else pad[nvar] = 0;
-    } else error->all(FLERR,"Illegal variable command");
+    } else error->all(FLERR,"Illegal variable loop command: too much arguments");
     num[nvar] = nlast;
     which[nvar] = nfirst-1;
     data[nvar] = new char*[1];
@@ -223,7 +224,7 @@ void Variable::set(int narg, char **arg)
   // error check that num = # of worlds in universe
 
   } else if (strcmp(arg[1],"world") == 0) {
-    if (narg < 3) error->all(FLERR,"Illegal variable command");
+    if (narg < 3) utils::missing_cmd_args(FLERR, "variable world", error);
     if (find(arg[0]) >= 0) return;
     if (nvar == maxvar) grow();
     style[nvar] = WORLD;
@@ -244,7 +245,7 @@ void Variable::set(int narg, char **arg)
 
   } else if (strcmp(arg[1],"universe") == 0 || strcmp(arg[1],"uloop") == 0) {
     if (strcmp(arg[1],"universe") == 0) {
-      if (narg < 3) error->all(FLERR,"Illegal variable command");
+      if (narg < 3) utils::missing_cmd_args(FLERR, "variable universe", error);
       if (find(arg[0]) >= 0) return;
       if (nvar == maxvar) grow();
       style[nvar] = UNIVERSE;
@@ -253,8 +254,10 @@ void Variable::set(int narg, char **arg)
       data[nvar] = new char*[num[nvar]];
       copy(num[nvar],&arg[2],data[nvar]);
     } else if (strcmp(arg[1],"uloop") == 0) {
-      if (narg < 3 || narg > 4 || (narg == 4 && strcmp(arg[3],"pad") != 0))
-        error->all(FLERR,"Illegal variable command");
+      if (narg < 3 || narg > 4)
+        error->all(FLERR,"Illegal variable command: expected 3 or 4 arguments but found {}", narg);
+      if (narg == 4 && strcmp(arg[3],"pad") != 0)
+        error->all(FLERR, "Invalid variable uloop argument: {}", arg[3]);
       if (find(arg[0]) >= 0) return;
       if (nvar == maxvar) grow();
       style[nvar] = ULOOP;
@@ -292,7 +295,7 @@ void Variable::set(int narg, char **arg)
   // data = 1 value, string to eval
 
   } else if (strcmp(arg[1],"string") == 0) {
-    if (narg != 3) error->all(FLERR,"Illegal variable command");
+    if (narg != 3) error->all(FLERR,"Illegal variable command: expected 3 arguments but found {}", narg);
 
     int maxcopy = strlen(arg[2]) + 1;
     int maxwork = maxcopy;
@@ -326,7 +329,7 @@ void Variable::set(int narg, char **arg)
   // data = 1 value, string to eval
 
   } else if (strcmp(arg[1],"getenv") == 0) {
-    if (narg != 3) error->all(FLERR,"Illegal variable command");
+    if (narg != 3) error->all(FLERR,"Illegal variable command: expected 3 arguments but found {}", narg);
     if (find(arg[0]) >= 0) {
       if (style[find(arg[0])] != GETENV)
         error->all(FLERR,"Cannot redefine variable as a different style");
@@ -346,7 +349,7 @@ void Variable::set(int narg, char **arg)
   // data = 1 value, string to eval
 
   } else if (strcmp(arg[1],"file") == 0) {
-    if (narg != 3) error->all(FLERR,"Illegal variable command");
+    if (narg != 3) error->all(FLERR,"Illegal variable command: expected 3 arguments but found {}", narg);
     if (find(arg[0]) >= 0) return;
     if (nvar == maxvar) grow();
     style[nvar] = SCALARFILE;
@@ -364,7 +367,7 @@ void Variable::set(int narg, char **arg)
   // data = nullptr
 
   } else if (strcmp(arg[1],"atomfile") == 0) {
-    if (narg != 3) error->all(FLERR,"Illegal variable command");
+    if (narg != 3) error->all(FLERR,"Illegal variable command: expected 3 arguments but found {}", narg);
     if (find(arg[0]) >= 0) return;
     if (nvar == maxvar) grow();
     style[nvar] = ATOMFILE;
@@ -384,7 +387,7 @@ void Variable::set(int narg, char **arg)
   //   3rd is filled on retrieval
 
   } else if (strcmp(arg[1],"format") == 0) {
-    if (narg != 4) error->all(FLERR,"Illegal variable command");
+    if (narg != 4) error->all(FLERR,"Illegal variable command: expected 4 arguments but found {}", narg);
     if (find(arg[0]) >= 0) return;
     if (nvar == maxvar) grow();
     style[nvar] = FORMAT;
@@ -404,7 +407,7 @@ void Variable::set(int narg, char **arg)
   // data = 2 values, 1st is string to eval, 2nd is filled on retrieval
 
   } else if (strcmp(arg[1],"equal") == 0) {
-    if (narg != 3) error->all(FLERR,"Illegal variable command");
+    if (narg != 3) error->all(FLERR,"Illegal variable command: expected 3 arguments but found {}", narg);
     int ivar = find(arg[0]);
     if (ivar >= 0) {
       if (style[ivar] != EQUAL)
@@ -430,7 +433,7 @@ void Variable::set(int narg, char **arg)
   // data = 1 value, string to eval
 
   } else if (strcmp(arg[1],"atom") == 0) {
-    if (narg != 3) error->all(FLERR,"Illegal variable command");
+    if (narg != 3) error->all(FLERR,"Illegal variable command: expected 3 arguments but found {}", narg);
     int ivar = find(arg[0]);
     if (ivar >= 0) {
       if (style[ivar] != ATOM)
@@ -454,7 +457,7 @@ void Variable::set(int narg, char **arg)
   // data = 1 value, string to eval
 
   } else if (strcmp(arg[1],"vector") == 0) {
-    if (narg != 3) error->all(FLERR,"Illegal variable command");
+    if (narg != 3) error->all(FLERR,"Illegal variable command: expected 3 arguments but found {}", narg);
     int ivar = find(arg[0]);
     if (ivar >= 0) {
       if (style[ivar] != VECTOR)
@@ -478,7 +481,7 @@ void Variable::set(int narg, char **arg)
   // data = 2 values, 1st is Python func to invoke, 2nd is filled by invoke
 
   } else if (strcmp(arg[1],"python") == 0) {
-    if (narg != 3) error->all(FLERR,"Illegal variable command");
+    if (narg != 3) error->all(FLERR,"Illegal variable command: expected 3 arguments but found {}", narg);
     if (!python->is_enabled())
       error->all(FLERR,"LAMMPS is not built with Python embedded");
     int ivar = find(arg[0]);
@@ -507,7 +510,7 @@ void Variable::set(int narg, char **arg)
   // dvalue = numeric initialization via platform::walltime()
 
   } else if (strcmp(arg[1],"timer") == 0) {
-    if (narg != 2) error->all(FLERR,"Illegal variable command");
+    if (narg != 2) error->all(FLERR,"Illegal variable command: expected 2 arguments but found {}", narg);
     int ivar = find(arg[0]);
     if (ivar >= 0) {
       if (style[ivar] != TIMER)
@@ -531,7 +534,7 @@ void Variable::set(int narg, char **arg)
   // dvalue = numeric initialization from 2nd arg, reset by internal_set()
 
   } else if (strcmp(arg[1],"internal") == 0) {
-    if (narg != 3) error->all(FLERR,"Illegal variable command");
+    if (narg != 3) error->all(FLERR,"Illegal variable command: expected 3 arguments but found {}", narg);
     int ivar = find(arg[0]);
     if (ivar >= 0) {
       if (style[ivar] != INTERNAL)
@@ -551,7 +554,7 @@ void Variable::set(int narg, char **arg)
 
   // unrecognized variable style
 
-  } else error->all(FLERR,"Illegal variable command");
+  } else error->all(FLERR,"Unknown variable keyword: {}", arg[1]);
 
   // set name of variable, if not replacing one flagged with replaceflag
   // name must be all alphanumeric chars or underscores

From 60b00bfa8fb12437989e882f1d01d6561fac7084 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Thu, 25 Aug 2022 05:48:07 -0400
Subject: [PATCH 8/8] update unit tests for variable command

---
 src/variable.cpp                     |  3 ++-
 unittest/commands/test_variables.cpp | 10 +++++-----
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/src/variable.cpp b/src/variable.cpp
index d6eec9eeb3..4117c41da6 100644
--- a/src/variable.cpp
+++ b/src/variable.cpp
@@ -170,7 +170,8 @@ void Variable::set(int narg, char **arg)
   // doesn't matter if variable no longer exists
 
   if (strcmp(arg[1],"delete") == 0) {
-    if (narg != 2) error->all(FLERR,"Illegal variable command: expected 2 argument but found {}", narg);
+    if (narg != 2)
+      error->all(FLERR,"Illegal variable delete command: expected 2 arguments but found {}", narg);
     if (find(arg[0]) >= 0) remove(find(arg[0]));
     return;
 
diff --git a/unittest/commands/test_variables.cpp b/unittest/commands/test_variables.cpp
index cf124eeafd..2b1beddd48 100644
--- a/unittest/commands/test_variables.cpp
+++ b/unittest/commands/test_variables.cpp
@@ -197,11 +197,11 @@ TEST_F(VariableTest, CreateDelete)
     ASSERT_EQ(variable->internalstyle(variable->find("ten")), 1);
 
     TEST_FAILURE(".*ERROR: Illegal variable command.*", command("variable"););
-    TEST_FAILURE(".*ERROR: Illegal variable command.*", command("variable dummy index"););
-    TEST_FAILURE(".*ERROR: Illegal variable command.*", command("variable dummy delete xxx"););
-    TEST_FAILURE(".*ERROR: Illegal variable command.*", command("variable dummy loop -1"););
-    TEST_FAILURE(".*ERROR: Illegal variable command.*", command("variable dummy loop 10 1"););
-    TEST_FAILURE(".*ERROR: Illegal variable command.*", command("variable dummy xxxx"););
+    TEST_FAILURE(".*ERROR: Illegal variable index command.*", command("variable dummy index"););
+    TEST_FAILURE(".*ERROR: Illegal variable delete command: expected 2 arguments but found 3.*", command("variable dummy delete xxx"););
+    TEST_FAILURE(".*ERROR: Invalid variable loop argument: -1.*", command("variable dummy loop -1"););
+    TEST_FAILURE(".*ERROR: Illegal variable loop command.*", command("variable dummy loop 10 1"););
+    TEST_FAILURE(".*ERROR: Unknown variable keyword: xxx.*", command("variable dummy xxxx"););
     TEST_FAILURE(".*ERROR: Cannot redefine variable as a different style.*",
                  command("variable two string xxx"););
     TEST_FAILURE(".*ERROR: Cannot redefine variable as a different style.*",