Substack should not be allowed to change columns

Disable the arguments append-column and delete-column of tabular-features.

The code is taken from InsetMathCases, with some changes
* no need to record undo here
* in dispatch, return is prefered to break, since we do not want to invoke
  InsetMathGrid::doDispatch.
Propagate these changes to InsetMathCases.

Cleanup of the InsetMathCases error messages to fit with other parts
of the code.

The handling of tabular-features in mathed needs to be unified somehow.

Based on a commit from lynx <lorenzobertini97@gmail.com>

Part of bug #12590.

src/mathed/InsetMathCases.cpp

@@ -61,19 +61,15 @@ void InsetMathCases::draw(PainterInfo & pi, int x, int y) const
 
 void InsetMathCases::doDispatch(Cursor & cur, FuncRequest & cmd)
 {
-	//lyxerr << "*** InsetMathCases: request: " << cmd << endl;
 	switch (cmd.action()) {
 	case LFUN_TABULAR_FEATURE: {
 		string s = cmd.getArg(0);
 		// vertical lines and adding/deleting columns is not allowed for \cases
-		// FIXME: "I suspect that the break after cur.undispatched() should be a
-		// return; the recordUndo seems bogus too." (lasgouttes)
 		if (s == "append-column" || s == "delete-column"
 		    || s == "add-vline-left" || s == "add-vline-right") {
 			cur.undispatched();
-			break;
+			return;
 		}
-		cur.recordUndo();
 	}
 	default:
 		break;
@@ -91,15 +87,15 @@ bool InsetMathCases::getStatus(Cursor & cur, FuncRequest const & cmd,
 		if (s == "add-vline-left" || s == "add-vline-right") {
 			flag.setEnabled(false);
 			flag.message(bformat(
-				from_utf8(N_("No vertical grid lines in 'cases': feature %1$s")),
+				from_utf8(N_("Can't add vertical grid lines in '%1$s'")),
-				from_utf8(s)));
+				from_utf8("cases")));
 			return true;
 		}
 		if (s == "append-column" || s == "delete-column") {
 			flag.setEnabled(false);
 			flag.message(bformat(
 				from_utf8(N_("Changing number of columns not allowed in "
-					     "'cases': feature %1$s")), from_utf8(s)));
+					     "'%1$s'")), from_utf8("cases")));
 			return true;
 		}
 		break;

src/mathed/InsetMathSubstack.cpp

@@ -15,6 +15,7 @@
 #include "MathData.h"
 #include "MathStream.h"
 
+#include "Cursor.h"
 #include "FuncRequest.h"
 #include "FuncStatus.h"
 #include "LaTeXFeatures.h"
@@ -59,6 +60,24 @@ void InsetMathSubstack::draw(PainterInfo & pi, int x, int y) const
 }
 
 
+void InsetMathSubstack::doDispatch(Cursor & cur, FuncRequest & cmd)
+{
+	switch (cmd.action()) {
+	case LFUN_TABULAR_FEATURE: {
+		string s = cmd.getArg(0);
+		if (s == "append-column" || s == "delete-column"
+			|| s == "add-vline-left" || s == "add-vline-right") {
+			cur.undispatched();
+			return;
+		}
+	}
+	default:
+		break;
+	}
+	InsetMathGrid::doDispatch(cur, cmd);
+}
+
+
 bool InsetMathSubstack::getStatus(Cursor & cur, FuncRequest const & cmd,
 		FuncStatus & flag) const
 {
@@ -81,6 +100,14 @@ bool InsetMathSubstack::getStatus(Cursor & cur, FuncRequest const & cmd,
 			flag.setEnabled(false);
 			return true;
 		}
+		// disallow changing number of columns
+		if (s == "append-column" || s == "delete-column") {
+			flag.setEnabled(false);
+			flag.message(bformat(
+				from_utf8(N_("Changing number of columns not allowed in "
+					     "'%1$s'")), from_utf8("substack")));
+			return true;
+		}
 		break;
 	}
 

src/mathed/InsetMathSubstack.h

@@ -31,6 +31,8 @@ public:
 	///
 	InsetMathSubstack const * asSubstackInset() const override { return this; }
 
+	///
+	void doDispatch(Cursor & cur, FuncRequest & cmd) override;
 	///
 	bool getStatus(Cursor & cur, FuncRequest const & cmd,
 		FuncStatus & flag) const override;