Always quote Python executable path

src/extension/common/stringUtils.ts

@@ -58,5 +58,8 @@ export function fileToCommandArgumentForPythonExt(source: string): string {
     if (!source) {
         return source;
     }
-    return toCommandArgumentForPythonExt(source).replace(/\\/g, '/');
+
+    let result = toCommandArgumentForPythonExt(source);
+
+    return result.replace(/\\/g, '/');
 }

src/extension/debugger/adapter/factory.ts

@@ -80,14 +80,20 @@ export class DebugAdapterDescriptorFactory implements IDebugAdapterDescriptorFac
 
             let executable = command.shift() ?? 'python';
 
+            // Always ensure interpreter/command is quoted if necessary. Previously this was
+            // only done in the debugAdapterPath branch which meant that in the common case
+            // (using the built‑in adapter path) an interpreter path containing spaces would
+            // be passed unquoted, resulting in a fork/spawn failure on Windows. See bug
+            // report for details.
+            executable = fileToCommandArgumentForPythonExt(executable);
+
             // "logToFile" is not handled directly by the adapter - instead, we need to pass
             // the corresponding CLI switch when spawning it.
             const logArgs = configuration.logToFile ? ['--log-dir', EXTENSION_ROOT_DIR] : [];
 
             if (configuration.debugAdapterPath !== undefined) {
                 const args = command.concat([configuration.debugAdapterPath, ...logArgs]);
                 traceLog(`DAP Server launched with command: ${executable} ${args.join(' ')}`);
-                executable = fileToCommandArgumentForPythonExt(executable);
                 return new DebugAdapterExecutable(executable, args);
             }
 

src/test/unittest/adapter/factory.unit.test.ts

@@ -304,7 +304,23 @@ suite('Debugging - Adapter Factory', () => {
 
         assert.deepStrictEqual(descriptor, debugExecutable);
     });
-    test('Add quotes to interpreter path with spaces', async () => {
+    test('Add quotes to interpreter path with spaces (default adapter path)', async () => {
+        const session = createSession({});
+        const interpreterPathSpaces = 'path/to/python interpreter with spaces';
+        const interpreterPathSpacesQuoted = `"${interpreterPathSpaces}"`;
+        const debugExecutable = new DebugAdapterExecutable(interpreterPathSpacesQuoted, [debugAdapterPath]);
+
+        getInterpreterDetailsStub.resolves({ path: [interpreterPathSpaces] });
+        const interpreterSpacePath: PythonEnvironment = createInterpreter(interpreterPathSpaces, '3.7.4-test');
+        // Add architecture for completeness.
+        (interpreterSpacePath as any).architecture = Architecture.Unknown;
+        resolveEnvironmentStub.withArgs(interpreterPathSpaces).resolves(interpreterSpacePath);
+        const descriptor = await factory.createDebugAdapterDescriptor(session, nodeExecutable);
+
+        assert.deepStrictEqual(descriptor, debugExecutable);
+    });
+
+    test('Add quotes to interpreter path with spaces when debugAdapterPath is specified', async () => {
         const customAdapterPath = 'custom/debug/adapter/customAdapterPath';
         const session = createSession({ debugAdapterPath: customAdapterPath });
         const interpreterPathSpaces = 'path/to/python interpreter with spaces';

src/test/unittest/adapter/remoteLaunchers.unit.test.ts

@@ -8,6 +8,7 @@ import * as path from 'path';
 import { EXTENSION_ROOT_DIR } from '../../../extension/common/constants';
 import '../../../extension/common/promiseUtils';
 import * as launchers from '../../../extension/debugger/adapter/remoteLaunchers';
+import { fileToCommandArgumentForPythonExt } from '../../../extension/common/stringUtils';
 
 suite('External debugpy Debugger Launcher', () => {
     [
@@ -18,7 +19,7 @@ suite('External debugpy Debugger Launcher', () => {
         },
         {
             testName: 'When path to debugpy contains spaces',
-            path: path.join('path', 'to', 'debugpy', 'with spaces'),
+            path: fileToCommandArgumentForPythonExt(path.join('path', 'to', 'debugpy', 'with spaces')),
             expectedPath: '"path/to/debugpy/with spaces"',
         },
     ].forEach((testParams) => {