Improve instruction operand edit edge case

The instruction operand editor has a shortcut button for editing a
project symbol.  Attempting to change the comment field twice
without closing the operand editor in between would result in a
complaint about duplicate symbol names.

Asm65/Label.cs

@@ -32,12 +32,16 @@ namespace Asm65 {
 
         /// <summary>
         /// String comparer to use when comparing labels.
-        /// 
+        /// </summary>
+        /// <remarks>
+        /// Usage:
+        ///   if (Label.LABEL_COMPARER.Equals(label1, label2)) { ... }
+        ///
         /// We may want case-insensitive string compares, and we want the "invariant culture"
         /// version for consistent results across users in multiple locales.  (The labels are
         /// expected to be ASCII strings, so the latter isn't crucial unless we change the
         /// allowed set.)
-        /// </summary>
+        /// </remarks>
         public static readonly StringComparer LABEL_COMPARER = LABELS_CASE_SENSITIVE ?
             StringComparer.InvariantCulture :
             StringComparer.InvariantCultureIgnoreCase;

SourceGen/WpfGui/EditDefSymbol.xaml.cs

@@ -277,10 +277,27 @@ namespace SourceGen.WpfGui {
                 out Symbol.LabelAnnotation unused4);
             bool labelUnique;
 
-            // NOTE: should be using Asm65.Label.LABEL_COMPARER?
             if (mDefSymbolList.TryGetValue(trimLabel, out DefSymbol existing)) {
-                // It's okay if it's the same object.
-                labelUnique = (existing == mOldSym);
+                // We found a match.  See if we're just seeing the symbol we're editing.
+                //
+                // We only want to check the label, not the entire symbol, because otherwise
+                // things can go funny when multiple edits are done without flushing the data
+                // back to the symbol table.  For example, when this is invoked from the
+                // Edit Project Symbol button in the instruction operand editor, the user might
+                // edit the comment field of an existing project symbol, hit OK here, then try
+                // to edit it again before closing the operand editor.  In that case we get
+                // passed the edited DefSymbol, which no longer fully matches what's in the
+                // symbol table.
+                //
+                // TODO: we still don't handle the case where the user changes the label from
+                // FOO to FOO1 and then back to FOO without closing the instruction edit dialog.
+                // The problem is that we find a match for FOO in the symbol table without
+                // realizing that it was the original name before the edits began.  To fix this
+                // we need to pass in the original label as well as the recently-edited symbol,
+                // and allow the new name to match either.
+
+                //labelUnique = (existing == mOldSym);
+                labelUnique = Asm65.Label.LABEL_COMPARER.Equals(existing.Label, mOldSym.Label);
             } else {
                 labelUnique = true;
             }

SourceGen/WpfGui/EditInstructionOperand.xaml.cs

@@ -917,7 +917,7 @@ namespace SourceGen.WpfGui {
                 // which will traverse multiple items to find a match.
                 // TODO: this can create a situation where the code list shows FUBAR-1 but we
                 // edit an earlier label, if the earlier label has a multi-byte format that
-                // includes the target address.  (An example can be found in 2024-ui-edge-cases.)
+                // includes the target address.  (An example can be found in 20200-ui-edge-cases.)
                 mEditedLabelOffset =
                     DataAnalysis.GetBaseOperandOffset(mProject, attr.OperandOffset);
                 mLabelTargetAddress = mProject.GetAnattrib(mEditedLabelOffset).Address;