Fix double semicolon in PATH environment variable on Windows (#748)

* Initial plan

* Fix double semicolon issue in PATH environment variable

Co-authored-by: eleanorjboyd <26030610+eleanorjboyd@users.noreply.github.com>

* clarify comments and shrink test scope

* linting

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: eleanorjboyd <26030610+eleanorjboyd@users.noreply.github.com>

Author: Copilot

src/extension/noConfigDebugInit.ts

@@ -77,7 +77,13 @@ export async function registerNoConfigDebug(
 
     const noConfigScriptsDir = path.join(extPath, 'bundled', 'scripts', 'noConfigScripts');
     const pathSeparator = process.platform === 'win32' ? ';' : ':';
-    collection.append('PATH', `${pathSeparator}${noConfigScriptsDir}`);
+
+    // Check if the current PATH already ends with a path separator to avoid double separators
+    const currentPath = process.env.PATH || '';
+    const needsSeparator = currentPath.length > 0 && !currentPath.endsWith(pathSeparator);
+    const pathValueToAppend = needsSeparator ? `${pathSeparator}${noConfigScriptsDir}` : noConfigScriptsDir;
+
+    collection.append('PATH', pathValueToAppend);
 
     const bundledDebugPath = path.join(extPath, 'bundled', 'libs', 'debugpy');
     collection.replace('BUNDLED_DEBUGPY_PATH', bundledDebugPath);

src/test/unittest/noConfigDebugInit.unit.test.ts

@@ -71,7 +71,7 @@ suite('setup for no-config debug scenario', function () {
             .setup((x) => x.append(TypeMoq.It.isAny(), TypeMoq.It.isAny()))
             .callback((key, value) => {
                 if (key === 'PATH') {
-                    assert(value === `:${noConfigScriptsDir}`);
+                    assert(value.includes(noConfigScriptsDir));
                 }
             })
             .returns(envVarCollectionAppendStub);
@@ -88,6 +88,100 @@ suite('setup for no-config debug scenario', function () {
         sinon.assert.calledOnce(envVarCollectionAppendStub);
     });
 
+    test('should not add extra separator when PATH already ends with separator', async () => {
+        const environmentVariableCollectionMock = TypeMoq.Mock.ofType<any>();
+        envVarCollectionReplaceStub = sinon.stub();
+        envVarCollectionAppendStub = sinon.stub();
+
+        // Simulate a PATH that already ends with a separator to test the fix
+        const pathSeparator = process.platform === 'win32' ? ';' : ':';
+        const originalPath = process.env.PATH;
+        process.env.PATH = `/some/path${pathSeparator}`;
+
+        try {
+            environmentVariableCollectionMock
+                .setup((x) => x.replace(TypeMoq.It.isAny(), TypeMoq.It.isAny()))
+                .returns(envVarCollectionReplaceStub);
+
+            environmentVariableCollectionMock
+                .setup((x) => x.append(TypeMoq.It.isAny(), TypeMoq.It.isAny()))
+                .callback((key, value) => {
+                    if (key === 'PATH') {
+                        // Since PATH already ends with separator, we should NOT add another one
+                        assert(value === noConfigScriptsDir);
+                        assert(!value.startsWith(pathSeparator));
+                    }
+                })
+                .returns(envVarCollectionAppendStub);
+
+            context
+                .setup((c) => c.environmentVariableCollection)
+                .returns(() => environmentVariableCollectionMock.object);
+
+            setupFileSystemWatchers();
+
+            // run init for no config debug
+            await registerNoConfigDebug(context.object.environmentVariableCollection, context.object.extensionPath);
+
+            // assert that append was called for PATH
+            sinon.assert.calledOnce(envVarCollectionAppendStub);
+        } finally {
+            // Restore original PATH
+            if (originalPath !== undefined) {
+                process.env.PATH = originalPath;
+            } else {
+                delete process.env.PATH;
+            }
+        }
+    });
+
+    test('should add separator when PATH does not end with separator', async () => {
+        const environmentVariableCollectionMock = TypeMoq.Mock.ofType<any>();
+        envVarCollectionReplaceStub = sinon.stub();
+        envVarCollectionAppendStub = sinon.stub();
+
+        // Simulate a PATH that does NOT end with a separator
+        const pathSeparator = process.platform === 'win32' ? ';' : ':';
+        const originalPath = process.env.PATH;
+        process.env.PATH = '/some/path';
+
+        try {
+            environmentVariableCollectionMock
+                .setup((x) => x.replace(TypeMoq.It.isAny(), TypeMoq.It.isAny()))
+                .returns(envVarCollectionReplaceStub);
+
+            environmentVariableCollectionMock
+                .setup((x) => x.append(TypeMoq.It.isAny(), TypeMoq.It.isAny()))
+                .callback((key, value) => {
+                    if (key === 'PATH') {
+                        // Since PATH does NOT end with separator, we should add one
+                        assert(value === `${pathSeparator}${noConfigScriptsDir}`);
+                        assert(value.startsWith(pathSeparator));
+                    }
+                })
+                .returns(envVarCollectionAppendStub);
+
+            context
+                .setup((c) => c.environmentVariableCollection)
+                .returns(() => environmentVariableCollectionMock.object);
+
+            setupFileSystemWatchers();
+
+            // run init for no config debug
+            await registerNoConfigDebug(context.object.environmentVariableCollection, context.object.extensionPath);
+
+            // assert that append was called for PATH
+            sinon.assert.calledOnce(envVarCollectionAppendStub);
+        } finally {
+            // Restore original PATH
+            if (originalPath !== undefined) {
+                process.env.PATH = originalPath;
+            } else {
+                delete process.env.PATH;
+            }
+        }
+    });
+
     test('should create file system watcher for debuggerAdapterEndpointFolder', async () => {
         // Arrange
         const environmentVariableCollectionMock = TypeMoq.Mock.ofType<any>();