fix: surface cmake --install output and add permission error hint

When cmake --install fails, the extension now:
1. Streams stdout/stderr to the Output channel via an OutputConsumer
   (matching the CPackOutputLogger pattern) so users see CMake's actual
   error messages instead of just an exit code.
2. Detects permission-related errors in the output and shows an
   actionable hint recommending cmake.installPrefix.

The containsPermissionError() utility is in installUtils.ts (no vscode
dependency) so it is testable in backend unit tests.

Adds 6 new unit tests for permission error detection.
Existing CMake: Install behavior is unchanged.

Co-authored-by: hanniavalera <90047725+hanniavalera@users.noreply.github.com>

Author: Copilot

src/cmakeProject.ts

@@ -54,7 +54,7 @@ import { DebugTrackerFactory, DebuggerInformation, getDebuggerPipeName } from '@
 import { NamedTarget, RichTarget, FolderTarget } from '@cmt/drivers/cmakeDriver';
 
 import { CommandResult, ConfigurationType } from 'vscode-cmake-tools';
-import { parseInstallComponentsFromContent } from '@cmt/installUtils';
+import { parseInstallComponentsFromContent, containsPermissionError } from '@cmt/installUtils';
 
 nls.config({ messageFormat: nls.MessageFormat.bundle, bundleFormat: nls.BundleFormat.standalone })();
 const localize: nls.LocalizeFunc = nls.loadMessageBundle();
@@ -2672,11 +2672,25 @@ export class CMakeProject {
             },
             async (_progress, cancel) => {
                 cancel.onCancellationRequested(() => rollbar.invokeAsync(localize('stop.on.cancellation', 'Stop on cancellation'), () => this.stop()));
-                const child = driver.executeCommand(cmake.path, args, undefined, {});
+                const consumer: proc.OutputConsumer = {
+                    output(line: string) {
+                        buildLogger.info(line);
+                    },
+                    error(line: string) {
+                        buildLogger.error(line);
+                    }
+                };
+                const child = driver.executeCommand(cmake.path, args, consumer, {});
                 const result = await child.result;
                 if (result.retc !== 0) {
                     buildLogger.error(localize('install.component.failed', 'Install component failed with exit code {0}', result.retc));
                     log.showChannel(true);
+                    const combinedOutput = [result.stdout, result.stderr].filter(s => s).join('\n');
+                    if (containsPermissionError(combinedOutput)) {
+                        void vscode.window.showErrorMessage(
+                            localize('install.component.permission.error',
+                                'Install failed due to a permission error. Consider setting "cmake.installPrefix" to a writable directory (e.g. $\{workspaceFolder}/_install).'));
+                    }
                 } else {
                     buildLogger.info(localize('install.component.finished', 'Install component finished successfully'));
                 }

src/installUtils.ts

@@ -16,3 +16,12 @@ export function parseInstallComponentsFromContent(content: string): string[] {
     }
     return Array.from(components).sort();
 }
+
+/**
+ * Check whether cmake --install output indicates a permission/access error.
+ * Used to provide an actionable hint to the user.
+ */
+export function containsPermissionError(output: string): boolean {
+    const lower = output.toLowerCase();
+    return lower.includes('permission') || lower.includes('access is denied') || lower.includes('cannot create directory');
+}

test/unit-tests/backend/installComponents.test.ts

@@ -1,5 +1,5 @@
 import { expect } from 'chai';
-import { parseInstallComponentsFromContent } from '@cmt/installUtils';
+import { parseInstallComponentsFromContent, containsPermissionError } from '@cmt/installUtils';
 
 suite('parseInstallComponentsFromContent', () => {
     test('parses single component', () => {
@@ -121,3 +121,32 @@ endif()
         expect(components).to.deep.equal(['my-component_v2']);
     });
 });
+
+suite('containsPermissionError', () => {
+    test('detects "permission" keyword', () => {
+        expect(containsPermissionError('file cannot copy: Permission denied')).to.be.true;
+    });
+
+    test('detects "cannot create directory" from CMake', () => {
+        expect(containsPermissionError(
+            'file cannot create directory: C:/Program Files/MyProject/include. Maybe need administrative privileges.'
+        )).to.be.true;
+    });
+
+    test('detects "Access is denied" (Windows)', () => {
+        expect(containsPermissionError('Error: Access is denied.')).to.be.true;
+    });
+
+    test('is case-insensitive', () => {
+        expect(containsPermissionError('PERMISSION DENIED')).to.be.true;
+        expect(containsPermissionError('Cannot Create Directory: /opt/app')).to.be.true;
+    });
+
+    test('returns false for unrelated errors', () => {
+        expect(containsPermissionError('CMake Error: install(TARGETS) given no ARCHIVE DESTINATION')).to.be.false;
+    });
+
+    test('returns false for empty string', () => {
+        expect(containsPermissionError('')).to.be.false;
+    });
+});