Fix flaky diagnostic added by declaration emit for untyped module imports

tsc/internal/checker/checker.go

@@ -15379,7 +15379,10 @@ func (c *Checker) getExternalModuleFileFromDeclaration(declaration *ast.Node) *a
 	if ast.HasImportAttributes(declaration) {
 		importAttributesType = c.getTypeFromImportAttributes(ast.GetImportAttributes(declaration))
 	}
-	moduleSymbol := c.resolveExternalModuleNameWorker(specifier, specifier /*moduleNotFoundError*/, nil, false, false, importAttributesType) // TODO: GH#18217
+	// This is only used by emit and type printing, after checking has already reported any
+	// resolution errors for this specifier. Resolve with ignoreErrors so that these queries
+	// don't add new diagnostics (e.g. an implicit-any-module suggestion) as a side effect.
+	moduleSymbol := c.resolveExternalModuleNameWorker(specifier, specifier, nil /*moduleNotFoundError*/, true /*ignoreErrors*/, false /*isForAugmentation*/, importAttributesType)
 	if moduleSymbol == nil {
 		return nil
 	}

tsc/internal/fourslash/fourslash.go

@@ -368,6 +368,9 @@ const showCodeLensLocationsCommandName = "typescript.showCodeLensLocations"
 func (f *FourslashTest) initialize(t *testing.T, capabilities *lsproto.ClientCapabilities, runExternalCode bool) {
 	initializationOptions := &lsproto.InitializationOptions{
 		CodeLensShowLocationsCommandName: new(showCodeLensLocationsCommandName),
+		// Make every textDocument/diagnostic request also emit the program and fail if the
+		// diagnostics differ before and after emit, e.g. because the emit resolver added some.
+		TrackFlakyDiagnostics: new(lsproto.DiagnosticFlakeLogLevelPanic),
 	}
 	if runExternalCode {
 		initializationOptions.RunExternalCode = new(true)

tsc/internal/fourslash/tests/noFlakyDiagnosticsUntypedModule1_test.go

@@ -0,0 +1,26 @@
+package fourslash_test
+
+import (
+	"testing"
+
+	"github.com/microsoft/TypeScript/tsc/internal/fourslash"
+	"github.com/microsoft/TypeScript/tsc/internal/testutil"
+)
+
+func TestNoFlakyDiagnosticsUntypedModule1(t *testing.T) {
+	t.Parallel()
+	defer testutil.RecoverAndFail(t, "Panic on fourslash test")
+	const content = `// @allowJs: true
+// @noImplicitAny: true
+// @declaration: true
+// @Filename: /node_modules/untyped/index.js
+// @noOpen: true
+exports.x = 1;
+// @Filename: /index.js
+import { x } from "untyped";
+x;`
+	f, done := fourslash.NewFourslash(t, nil /*capabilities*/, content)
+	defer done()
+	f.GoToFile(t, "/index.js")
+	f.VerifySuggestionDiagnostics(t, nil)
+}

tsc/internal/fourslash/tests/noFlakyDiagnosticsUntypedModule2_test.go

@@ -0,0 +1,25 @@
+package fourslash_test
+
+import (
+	"testing"
+
+	"github.com/microsoft/TypeScript/tsc/internal/fourslash"
+	"github.com/microsoft/TypeScript/tsc/internal/testutil"
+)
+
+func TestNoFlakyDiagnosticsUntypedModule2(t *testing.T) {
+	t.Parallel()
+	defer testutil.RecoverAndFail(t, "Panic on fourslash test")
+	const content = `// @noImplicitAny: true
+// @declaration: true
+// @Filename: /untyped.js
+exports.x = 1;
+// @Filename: /index.ts
+// @ts-expect-error
+import { x } from "./untyped";
+x;`
+	f, done := fourslash.NewFourslash(t, nil /*capabilities*/, content)
+	defer done()
+	f.GoToFile(t, "/index.ts")
+	f.VerifySuggestionDiagnostics(t, nil)
+}

tsc/internal/fourslash/tests/noFlakyDiagnosticsUntypedModule3_test.go

@@ -0,0 +1,26 @@
+package fourslash_test
+
+import (
+	"testing"
+
+	"github.com/microsoft/TypeScript/tsc/internal/fourslash"
+	"github.com/microsoft/TypeScript/tsc/internal/testutil"
+)
+
+func TestNoFlakyDiagnosticsUntypedModule3(t *testing.T) {
+	t.Parallel()
+	defer testutil.RecoverAndFail(t, "Panic on fourslash test")
+	const content = `// @module: nodenext
+// @noImplicitAny: true
+// @declaration: true
+// @Filename: /untyped.mjs
+export const x = 1;
+// @Filename: /index.mts
+// @ts-expect-error
+import { x } from "./untyped.mjs";
+x;`
+	f, done := fourslash.NewFourslash(t, nil /*capabilities*/, content)
+	defer done()
+	f.GoToFile(t, "/index.mts")
+	f.VerifySuggestionDiagnostics(t, nil)
+}