Add source code highlighting (#224)

* Add source file highlighting support
* Change highlighting colour to grey

Author: omarArm

src/SourceFileHighlighting.ts

@@ -0,0 +1,115 @@
+/*********************************************************************
+ * Copyright (c) 2026 Arm Limited and others
+ *
+ * This program and the accompanying materials are made
+ * available under the terms of the Eclipse Public License 2.0
+ * which is available at https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *********************************************************************/
+
+import * as vscode from 'vscode';
+import { DebugProtocol } from '@vscode/debugprotocol';
+
+export class SourceFileHighlighting {
+    private activeDebugSession: vscode.DebugSession | undefined;
+    private context: vscode.ExtensionContext;
+    private executableLineDecorator =
+        vscode.window.createTextEditorDecorationType({
+            borderWidth: '0 0 0 2px',
+            borderStyle: 'solid',
+            borderColor: new vscode.ThemeColor('editorLineNumber.foreground'),
+            isWholeLine: true,
+        });
+
+    constructor(context: vscode.ExtensionContext) {
+        this.context = context;
+    }
+
+    public activate(): void {
+        this.registerToEvents();
+    }
+
+    private registerToEvents(): void {
+        const onDidChangeActiveDebugSessionDisposable =
+            vscode.debug.onDidChangeActiveDebugSession((session) => {
+                if (!session) {
+                    this.clearExecutableLineDecorations(
+                        vscode.window.visibleTextEditors
+                    );
+                }
+                this.activeDebugSession = session;
+                this.handleOnDidChangeActiveTextEditor(
+                    vscode.window.activeTextEditor
+                );
+            });
+        const onDidChangeActiveTextEditorDisposable =
+            vscode.window.onDidChangeActiveTextEditor((editor) => {
+                this.handleOnDidChangeActiveTextEditor(editor);
+            });
+
+        this.context.subscriptions.push(
+            onDidChangeActiveDebugSessionDisposable,
+            onDidChangeActiveTextEditorDisposable
+        );
+    }
+
+    private clearExecutableLineDecorations(
+        editors: readonly vscode.TextEditor[]
+    ): void {
+        for (const editor of editors) {
+            editor.setDecorations(this.executableLineDecorator, []);
+        }
+    }
+
+    private async handleOnDidChangeActiveTextEditor(
+        editor: vscode.TextEditor | undefined
+    ): Promise<void> {
+        if (!editor) {
+            return;
+        }
+        if (!this.activeDebugSession) {
+            this.clearExecutableLineDecorations([editor]);
+            return;
+        }
+        const breakpointLocations = await this.getBreakpointLocations(editor);
+        if (!breakpointLocations) {
+            this.clearExecutableLineDecorations([editor]);
+            return;
+        }
+        const executableLines = new Set(
+            breakpointLocations.breakpoints.map(
+                (bp: DebugProtocol.BreakpointLocation) => bp.line
+            )
+        );
+        const decorations: vscode.DecorationOptions[] = Array.from(
+            executableLines
+        ).map((exeline: number) => {
+            const line = exeline - 1; // Convert to 0-based index
+            return {
+                range: new vscode.Range(line, 0, line, 0),
+            };
+        });
+        editor.setDecorations(this.executableLineDecorator, decorations);
+    }
+
+    private async getBreakpointLocations(
+        editor: vscode.TextEditor
+    ): Promise<DebugProtocol.BreakpointLocationsResponse['body'] | void> {
+        if (editor.document.uri.scheme !== 'file') {
+            return;
+        }
+        const currentSourceFile = editor.document.fileName;
+        const args: DebugProtocol.BreakpointLocationsArguments = {
+            source: { path: currentSourceFile },
+            line: 1,
+            endLine: editor.document.lineCount, // Requesting breakpoint locations for the whole file
+        };
+        const breakpointLocations =
+            await this.activeDebugSession?.customRequest(
+                'breakpointLocations',
+                args
+            );
+        return breakpointLocations;
+    }
+}

src/extension.ts

@@ -19,13 +19,15 @@ export { CustomReset } from './CustomReset';
 import { SwitchRadix } from './switchRadix';
 export { SwitchRadix } from './switchRadix';
 import { BreakpointModesController } from './BreakpointModesController';
+import { SourceFileHighlighting } from './SourceFileHighlighting';
 
 export function activate(context: ExtensionContext) {
     new MemoryServer(context);
     new ResumeAllSession(context);
     new SuspendAllSession(context);
     new CustomReset(context);
     new SwitchRadix(context);
+    new SourceFileHighlighting(context).activate();
     context.subscriptions.push(
         commands.registerCommand('cdt.debug.askProgramPath', (_config) => {
             return window.showInputBox({