Elide empty named imports next to a default import under verbatimModuleSyntax (#64578)

Co-authored-by: Ryan Cavanaugh <RyanCavanaugh@users.noreply.github.com>

Author: maksim-romanov

tsc/internal/transformers/tstransforms/typeeraser.go

@@ -316,6 +316,13 @@ func (tx *TypeEraserTransformer) visit(node *ast.Node) *ast.Node {
 		}
 		name := n.Name()
 		namedBindings := tx.Visitor().VisitNode(n.NamedBindings)
+		// Empty {} due to type-only import erasure can be skipped if there is also a default import
+		if name != nil && namedBindings != nil && ast.IsNamedImports(namedBindings) &&
+			len(namedBindings.AsNamedImports().Elements.Nodes) == 0 &&
+			len(n.NamedBindings.AsNamedImports().Elements.Nodes) != 0 {
+			// the default binding keeps the import; a source-written {} is left as is
+			namedBindings = nil
+		}
 		if name == nil && namedBindings == nil {
 			// all import bindings were elided
 			return nil

tsc/testdata/baselines/reference/compiler/verbatimModuleSyntaxDefaultImportTypeOnlyNamed.js

@@ -0,0 +1,32 @@
+//// [tests/cases/compiler/verbatimModuleSyntaxDefaultImportTypeOnlyNamed.ts] ////
+
+//// [a.ts]
+export default class A {}
+export type T = number;
+export const v = 0;
+
+//// [b.ts]
+import A1, { type T } from "./a";
+import A2, { type T as T2, v } from "./a";
+import { type T as T3 } from "./a";
+import A4, {} from "./a";
+import A5, { /* comment */ type T as T5 } from "./a";
+import A6, {
+    type T as T6,
+} from "./a";
+
+export { A1, A2, A4, A5, A6, v };
+
+
+//// [a.js]
+export default class A {
+}
+export const v = 0;
+//// [b.js]
+import A1 from "./a";
+import A2, { v } from "./a";
+import {} from "./a";
+import A4, {} from "./a";
+import A5 from "./a";
+import A6 from "./a";
+export { A1, A2, A4, A5, A6, v };

tsc/testdata/baselines/reference/compiler/verbatimModuleSyntaxDefaultImportTypeOnlyNamed.symbols

@@ -0,0 +1,52 @@
+//// [tests/cases/compiler/verbatimModuleSyntaxDefaultImportTypeOnlyNamed.ts] ////
+
+=== /a.ts ===
+export default class A {}
+>A : Symbol(A, Decl(a.ts, 0, 0))
+
+export type T = number;
+>T : Symbol(T, Decl(a.ts, 0, 25))
+
+export const v = 0;
+>v : Symbol(v, Decl(a.ts, 2, 12))
+
+=== /b.ts ===
+import A1, { type T } from "./a";
+>A1 : Symbol(A1, Decl(b.ts, 0, 6))
+>T : Symbol(T, Decl(b.ts, 0, 12))
+
+import A2, { type T as T2, v } from "./a";
+>A2 : Symbol(A2, Decl(b.ts, 1, 6))
+>T : Symbol(T, Decl(a.ts, 0, 25))
+>T2 : Symbol(T2, Decl(b.ts, 1, 12))
+>v : Symbol(v, Decl(b.ts, 1, 26))
+
+import { type T as T3 } from "./a";
+>T : Symbol(T, Decl(a.ts, 0, 25))
+>T3 : Symbol(T3, Decl(b.ts, 2, 8))
+
+import A4, {} from "./a";
+>A4 : Symbol(A4, Decl(b.ts, 3, 6))
+
+import A5, { /* comment */ type T as T5 } from "./a";
+>A5 : Symbol(A5, Decl(b.ts, 4, 6))
+>T : Symbol(T, Decl(a.ts, 0, 25))
+>T5 : Symbol(T5, Decl(b.ts, 4, 12))
+
+import A6, {
+>A6 : Symbol(A6, Decl(b.ts, 5, 6))
+
+    type T as T6,
+>T : Symbol(T, Decl(a.ts, 0, 25))
+>T6 : Symbol(T6, Decl(b.ts, 5, 12))
+
+} from "./a";
+
+export { A1, A2, A4, A5, A6, v };
+>A1 : Symbol(A1, Decl(b.ts, 9, 8))
+>A2 : Symbol(A2, Decl(b.ts, 9, 12))
+>A4 : Symbol(A4, Decl(b.ts, 9, 16))
+>A5 : Symbol(A5, Decl(b.ts, 9, 20))
+>A6 : Symbol(A6, Decl(b.ts, 9, 24))
+>v : Symbol(v, Decl(b.ts, 9, 28))
+

tsc/testdata/baselines/reference/compiler/verbatimModuleSyntaxDefaultImportTypeOnlyNamed.types

@@ -0,0 +1,53 @@
+//// [tests/cases/compiler/verbatimModuleSyntaxDefaultImportTypeOnlyNamed.ts] ////
+
+=== /a.ts ===
+export default class A {}
+>A : A
+
+export type T = number;
+>T : number
+
+export const v = 0;
+>v : 0
+>0 : 0
+
+=== /b.ts ===
+import A1, { type T } from "./a";
+>A1 : typeof A1
+>T : any
+
+import A2, { type T as T2, v } from "./a";
+>A2 : typeof A1
+>T : any
+>T2 : any
+>v : 0
+
+import { type T as T3 } from "./a";
+>T : any
+>T3 : any
+
+import A4, {} from "./a";
+>A4 : typeof A1
+
+import A5, { /* comment */ type T as T5 } from "./a";
+>A5 : typeof A1
+>T : any
+>T5 : any
+
+import A6, {
+>A6 : typeof A1
+
+    type T as T6,
+>T : any
+>T6 : any
+
+} from "./a";
+
+export { A1, A2, A4, A5, A6, v };
+>A1 : typeof A1
+>A2 : typeof A1
+>A4 : typeof A1
+>A5 : typeof A1
+>A6 : typeof A1
+>v : 0
+

tsc/testdata/tests/cases/compiler/verbatimModuleSyntaxDefaultImportTypeOnlyNamed.ts

@@ -0,0 +1,21 @@
+// @target: esnext
+// @module: esnext
+// @moduleResolution: bundler
+// @verbatimModuleSyntax: true
+
+// @Filename: /a.ts
+export default class A {}
+export type T = number;
+export const v = 0;
+
+// @Filename: /b.ts
+import A1, { type T } from "./a";
+import A2, { type T as T2, v } from "./a";
+import { type T as T3 } from "./a";
+import A4, {} from "./a";
+import A5, { /* comment */ type T as T5 } from "./a";
+import A6, {
+    type T as T6,
+} from "./a";
+
+export { A1, A2, A4, A5, A6, v };