Add toolbar button for "Go to Last Change"

Also, updated a couple of comments.

SourceGen/AsmGen/AsmAcme.cs

@@ -221,6 +221,8 @@ namespace SourceGen.AsmGen {
 
             mLocalizer = new LabelLocalizer(Project);
             if (!Settings.GetBool(AppSettings.SRCGEN_DISABLE_LABEL_LOCALIZATION, false)) {
+                // While '.' labels are limited to the current zone, '@' labels are visible
+                // between global labels.  (This is poorly documented.)
                 mLocalizer.LocalPrefix = "@";
                 mLocalizer.Analyze();
             }
@@ -503,6 +505,10 @@ namespace SourceGen.AsmGen {
         // IGenerator
         public void OutputLocalVariableTable(int offset, List<DefSymbol> newDefs,
                 LocalVariableTable allDefs) {
+            // We can do better here, but it requires knowing whether anything in "newDefs"
+            // overwrote a previous entry.  If everything is new, we don't need to start
+            // a new zone, and can just output newDefs.  (We don't need to start a new zone
+            // on a "clear previous".)
             OutputLine(string.Empty, "!zone", "Z" + offset.ToString("x6"), string.Empty);
             for (int i = 0; i < allDefs.Count; i++) {
                 DefSymbol defSym = allDefs[i];

SourceGen/Res/CommandIcons.xaml

@@ -49,6 +49,30 @@
         </Viewbox>
     </ControlTemplate>
 
+    <ControlTemplate x:Key="icon_DebugHistorySeekToFrame">
+        <!-- This file was generated by the AiToXaml tool.-->
+        <!-- Tool Version: 14.0.22307.0 -->
+        <Viewbox Width="16" Height="16" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+                 Style="{StaticResource DisableFade}">
+            <Rectangle Width="16" Height="16">
+                <Rectangle.Fill>
+                    <DrawingBrush>
+                        <DrawingBrush.Drawing>
+                            <DrawingGroup>
+                                <DrawingGroup.Children>
+                                    <GeometryDrawing Brush="#00FFFFFF" Geometry="F1M16,16L0,16 0,0 16,0z" />
+                                    <GeometryDrawing Brush="#FFF6F6F6" Geometry="F1M8,10L4,10 4,13 3,13 3,8.164 4.604,9.768 8,6.371z M6,1L6,2.629 4.604,1.232 2.482,3.354 3.129,4 2.5,4C1.122,4,0,5.122,0,6.5L0,13.5C0,14.879,1.122,16,2.5,16L7,16 16,16 16,1z" />
+                                    <GeometryDrawing Brush="#FF424242" Geometry="F1M7,3L15,3 15,2 7,2z M9,9L15,9 15,8 9,8z M9,6L15,6 15,5 9,5z M8,15L15,15 15,14 8,14z M5,11L15,11 15,12 5,12z" />
+                                    <GeometryDrawing Brush="#FF00529C" Geometry="F1M2.5,14L6,14 6,15 2.5,15C1.673,15,1,14.327,1,13.5L1,6.5C1,5.673,1.673,5,2.5,5L5.543,5 3.896,3.354 4.604,2.646 7.457,5.5 4.604,8.354 3.896,7.646 5.543,6 2.5,6C2.224,6,2,6.224,2,6.5L2,13.5C2,13.775,2.224,14,2.5,14" />
+                                </DrawingGroup.Children>
+                            </DrawingGroup>
+                        </DrawingBrush.Drawing>
+                    </DrawingBrush>
+                </Rectangle.Fill>
+            </Rectangle>
+        </Viewbox>
+    </ControlTemplate>
+
     <ControlTemplate x:Key="icon_F1Help">
         <!-- This file was generated by the AiToXaml tool.-->
         <!-- Tool Version: 14.0.22307.0 -->

SourceGen/Symbol.cs

@@ -38,8 +38,7 @@ namespace SourceGen {
 
         /// <summary>
         /// Local internal label, global internal label, or reference to an
-        /// external address?  Constants get a separate type in case we need to
-        /// distinguish them from addresses.
+        /// external address?  Constants get a separate type.
         /// </summary>
         public enum Type {
             Unknown = 0,
@@ -59,7 +58,7 @@ namespace SourceGen {
         }
 
         /// <summary>
-        ///  True if the symbol is a local variable.
+        /// True if the symbol is a local variable.
         /// </summary>
         public bool IsVariable {
             get { return SymbolSource == Source.Variable; }

SourceGen/WpfGui/MainWindow.xaml

@@ -421,6 +421,10 @@ limitations under the License.
                         ToolTip="Navigate forward (Alt+Right or Ctrl+Shift+Minus)">
                     <ContentControl Template="{StaticResource icon_StepForward}"/>
                 </Button>
+                <Button Command="{StaticResource GotoLastChangeCmd}"
+                        ToolTip="Go to Last Change">
+                    <ContentControl Template="{StaticResource icon_DebugHistorySeekToFrame}"/>
+                </Button>
                 <Separator/>
                 <Button Command="{StaticResource NewProjectCmd}" ToolTip="Create new project">
                     <ContentControl Template="{StaticResource icon_NewFile}"/>