fix: prevent duplicate setting error dialogs when global scope is deferred

When a workspace folder resolves, setting errors are now bundled into the
deferred global-scope background handler so notifyUserOfSettingErrors is
called once with the combined workspace + global errors, not twice.

Addresses review feedback from StellaHuang95 on PR microsoft#1456.

Author: eleanorjboyd

src/features/interpreterSelection.ts

@@ -376,23 +376,25 @@ export async function applyInitialEnvironmentSelection(
 
     if (workspaceFolderResolved) {
         // Defer global scope so it doesn't block post-selection startup.
+        // Bundle workspace errors into the background handler so we notify once (not twice).
         traceInfo('[interpreterSelection] Workspace env resolved, deferring global scope to background');
+        const deferredWorkspaceErrors = [...allErrors];
         resolveGlobalScope()
             .then(async (globalErrors) => {
-                if (globalErrors.length > 0) {
-                    await notifyUserOfSettingErrors(globalErrors);
+                const combined = [...deferredWorkspaceErrors, ...globalErrors];
+                if (combined.length > 0) {
+                    await notifyUserOfSettingErrors(combined);
                 }
             })
             .catch((err) => traceError(`[interpreterSelection] Background global scope resolution failed: ${err}`));
     } else {
         // No workspace folder resolved — global scope is the primary fallback, must await.
         const globalErrors = await resolveGlobalScope();
         allErrors.push(...globalErrors);
-    }
 
-    // Notify user if any settings could not be applied (workspace + global when awaited)
-    if (allErrors.length > 0) {
-        await notifyUserOfSettingErrors(allErrors);
+        if (allErrors.length > 0) {
+            await notifyUserOfSettingErrors(allErrors);
+        }
     }
 
     // Duration measures blocking time only (excludes deferred global scope).

src/test/features/interpreterSelection.unit.test.ts

@@ -811,6 +811,15 @@ suite('Interpreter Selection - applyInitialEnvironmentSelection', () => {
 
         const showWarnStub = sandbox.stub(windowApis, 'showWarningMessage').resolves(undefined);
 
+        // Wait for the deferred background handler (notification is bundled with global scope)
+        let resolveGlobalDone!: () => void;
+        const globalDone = new Promise<void>((resolve) => {
+            resolveGlobalDone = resolve;
+        });
+        mockEnvManagers.setEnvironments.callsFake(async () => {
+            resolveGlobalDone();
+        });
+
         await applyInitialEnvironmentSelection(
             mockEnvManagers as unknown as EnvironmentManagers,
             mockProjectManager as unknown as PythonProjectManager,
@@ -821,6 +830,10 @@ suite('Interpreter Selection - applyInitialEnvironmentSelection', () => {
         // Should still set the environment (falls through to auto-discovery)
         assert.ok(mockEnvManagers.setEnvironment.called, 'setEnvironment should be called via fallback');
 
+        // Wait for background global scope + notification handler
+        await globalDone;
+        await new Promise<void>((resolve) => process.nextTick(resolve));
+
         // Should show a warning about the unregistered manager
         assert.ok(showWarnStub.called, 'showWarningMessage should be called for unregistered pythonProjects manager');
     });
@@ -838,6 +851,15 @@ suite('Interpreter Selection - applyInitialEnvironmentSelection', () => {
 
         const showWarnStub = sandbox.stub(windowApis, 'showWarningMessage').resolves(undefined);
 
+        // Wait for the deferred background handler (notification is bundled with global scope)
+        let resolveGlobalDone!: () => void;
+        const globalDone = new Promise<void>((resolve) => {
+            resolveGlobalDone = resolve;
+        });
+        mockEnvManagers.setEnvironments.callsFake(async () => {
+            resolveGlobalDone();
+        });
+
         await applyInitialEnvironmentSelection(
             mockEnvManagers as unknown as EnvironmentManagers,
             mockProjectManager as unknown as PythonProjectManager,
@@ -848,6 +870,10 @@ suite('Interpreter Selection - applyInitialEnvironmentSelection', () => {
         // Should still set the environment (falls through to auto-discovery)
         assert.ok(mockEnvManagers.setEnvironment.called, 'setEnvironment should be called via fallback');
 
+        // Wait for background global scope + notification handler
+        await globalDone;
+        await new Promise<void>((resolve) => process.nextTick(resolve));
+
         // Should show a warning about the unregistered manager
         assert.ok(showWarnStub.called, 'showWarningMessage should be called for unregistered defaultEnvManager');
     });
@@ -955,13 +981,26 @@ suite('Interpreter Selection - applyInitialEnvironmentSelection', () => {
 
         const showWarnStub = sandbox.stub(windowApis, 'showWarningMessage').resolves(undefined);
 
+        // Wait for the deferred background handler (notification is bundled with global scope)
+        let resolveGlobalDone!: () => void;
+        const globalDone = new Promise<void>((resolve) => {
+            resolveGlobalDone = resolve;
+        });
+        mockEnvManagers.setEnvironments.callsFake(async () => {
+            resolveGlobalDone();
+        });
+
         await applyInitialEnvironmentSelection(
             mockEnvManagers as unknown as EnvironmentManagers,
             mockProjectManager as unknown as PythonProjectManager,
             mockNativeFinder as unknown as NativePythonFinder,
             mockApi as unknown as PythonEnvironmentApi,
         );
 
+        // Wait for background global scope + notification handler
+        await globalDone;
+        await new Promise<void>((resolve) => process.nextTick(resolve));
+
         assert.ok(showWarnStub.called, 'showWarningMessage should be called for unresolvable defaultInterpreterPath');
         const warningMessage = showWarnStub.firstCall.args[0] as string;
         assert.ok(warningMessage.includes('/nonexistent/python'), 'Warning message should include the configured path');