BUG: dangling dictionary reference for expression BCs

- exposed by the new embedded function handling.

  Requires local copies of dictionary content instead
  (similar to coded BCs handling)

BUG: incorrect formatting for expression function output

ENH: simpler copyDict version taking wordList instead of wordRes

- corresponds to the most common use case at the moment

ENH: expression string writeEntry method

- write as verbatim for better readability

src/OpenFOAM/expressions/exprString/exprString.C

@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -86,4 +86,36 @@ Foam::expressions::exprString::expand
 }
 
 
+bool Foam::expressions::exprString::writeEntry
+(
+    const word& keyword,
+    Ostream& os,
+    bool writeEmpty
+) const
+{
+    const bool ok = (writeEmpty || !empty());
+
+    if (ok)
+    {
+        if (!keyword.empty())
+        {
+            os.writeKeyword(keyword);
+        }
+
+        // Write as regular or verbatim string
+
+        token tok(*this);
+        if (!empty())
+        {
+            tok.setType(token::tokenType::VERBATIM);
+        }
+
+        os.write(tok);
+        os.endEntry();
+    }
+
+    return ok;
+}
+
+
 // ************************************************************************* //

src/OpenFOAM/expressions/exprString/exprString.H

@@ -183,6 +183,19 @@ public:
 
         //- Move assign from string. No expansions, no comment stripping
         inline exprString& operator=(std::string&& str);
+
+
+    // Write
+
+        //- Dictionary entry for expression string, normally suppressing
+        //- empty strings. Generally used verbatim output (readability)
+        //  \return true if entry was written
+        bool writeEntry
+        (
+            const word& keyword,
+            Ostream& os,
+            bool writeEmpty = false
+        ) const;
 };