Tighten heuristic for definite dts moduleness to check for syntactic default exports

Author: weswigham

src/compiler/checker.ts

@@ -1730,14 +1730,25 @@ namespace ts {
                 : resolveSymbol(moduleSymbol.exports.get(name), dontResolveAlias);
         }
 
+        function isSyntacticDefault(node: Node) {
+            if (isExportAssignment(node) && !node.isExportEquals) {
+                return true;
+            }
+            if (hasModifier(node, ModifierFlags.Default)) {
+                return true;
+            }
+            return false;
+        }
+
         function canHaveSyntheticDefault(file: SourceFile | undefined, moduleSymbol: Symbol, dontResolveAlias: boolean) {
             if (!allowSyntheticDefaultImports) {
                 return false;
             }
             // Declaration files (and ambient modules)
             if (!file || file.isDeclarationFile) {
-                // Definitely cannot have a synthetic default if they have a default member specified
-                if (resolveExportByName(moduleSymbol, InternalSymbolName.Default, dontResolveAlias)) {
+                // Definitely cannot have a synthetic default if they have a syntactic default member specified
+                const defaultExportSymbol = resolveExportByName(moduleSymbol, InternalSymbolName.Default, dontResolveAlias);
+                if (defaultExportSymbol && defaultExportSymbol.valueDeclaration && isSyntacticDefault(defaultExportSymbol.valueDeclaration)) {
                     return false;
                 }
                 // It _might_ still be incorrect to assume there is no __esModule marker on the import at runtime, even if there is no `default` member
@@ -1777,7 +1788,7 @@ namespace ts {
                 if (!exportDefaultSymbol && !hasSyntheticDefault) {
                     error(node.name, Diagnostics.Module_0_has_no_default_export, symbolToString(moduleSymbol));
                 }
-                else if (!exportDefaultSymbol && hasSyntheticDefault) {
+                else if (hasSyntheticDefault) {
                     // per emit behavior, a synthetic default overrides a "real" .default member if `__esModule` is not present
                     return resolveExternalModuleSymbol(moduleSymbol, dontResolveAlias) || resolveSymbol(moduleSymbol, dontResolveAlias);
                 }

tests/baselines/reference/esModuleInteropDefaultMemberMustBeSyntacticallyDefaultExport.js

@@ -0,0 +1,29 @@
+//// [tests/cases/compiler/esModuleInteropDefaultMemberMustBeSyntacticallyDefaultExport.ts] ////
+
+//// [point.d.ts]
+declare class Point {
+    x: number;
+    y: number;
+
+    constructor(x: number, y: number);
+
+    static default: "foo";
+}
+
+export = Point;
+//// [index.ts]
+import Point from "./point";
+
+const C = Point;
+const p = new C(1, 2);
+
+
+//// [index.js]
+"use strict";
+var __importDefault = (this && this.__importDefault) || function (mod) {
+    return (mod && mod.__esModule) ? mod : { "default": mod };
+};
+exports.__esModule = true;
+var point_1 = __importDefault(require("./point"));
+var C = point_1["default"];
+var p = new C(1, 2);

tests/baselines/reference/esModuleInteropDefaultMemberMustBeSyntacticallyDefaultExport.symbols

@@ -0,0 +1,33 @@
+=== tests/cases/compiler/point.d.ts ===
+declare class Point {
+>Point : Symbol(Point, Decl(point.d.ts, 0, 0))
+
+    x: number;
+>x : Symbol(Point.x, Decl(point.d.ts, 0, 21))
+
+    y: number;
+>y : Symbol(Point.y, Decl(point.d.ts, 1, 14))
+
+    constructor(x: number, y: number);
+>x : Symbol(x, Decl(point.d.ts, 4, 16))
+>y : Symbol(y, Decl(point.d.ts, 4, 26))
+
+    static default: "foo";
+>default : Symbol(Point.default, Decl(point.d.ts, 4, 38))
+}
+
+export = Point;
+>Point : Symbol(Point, Decl(point.d.ts, 0, 0))
+
+=== tests/cases/compiler/index.ts ===
+import Point from "./point";
+>Point : Symbol(Point, Decl(index.ts, 0, 6))
+
+const C = Point;
+>C : Symbol(C, Decl(index.ts, 2, 5))
+>Point : Symbol(Point, Decl(index.ts, 0, 6))
+
+const p = new C(1, 2);
+>p : Symbol(p, Decl(index.ts, 3, 5))
+>C : Symbol(C, Decl(index.ts, 2, 5))
+

tests/baselines/reference/esModuleInteropDefaultMemberMustBeSyntacticallyDefaultExport.types

@@ -0,0 +1,36 @@
+=== tests/cases/compiler/point.d.ts ===
+declare class Point {
+>Point : Point
+
+    x: number;
+>x : number
+
+    y: number;
+>y : number
+
+    constructor(x: number, y: number);
+>x : number
+>y : number
+
+    static default: "foo";
+>default : "foo"
+}
+
+export = Point;
+>Point : Point
+
+=== tests/cases/compiler/index.ts ===
+import Point from "./point";
+>Point : typeof Point
+
+const C = Point;
+>C : typeof Point
+>Point : typeof Point
+
+const p = new C(1, 2);
+>p : Point
+>new C(1, 2) : Point
+>C : typeof Point
+>1 : 1
+>2 : 2
+

tests/cases/compiler/esModuleInteropDefaultMemberMustBeSyntacticallyDefaultExport.ts

@@ -0,0 +1,17 @@
+// @esModuleInterop: true
+// @filename: point.d.ts
+declare class Point {
+    x: number;
+    y: number;
+
+    constructor(x: number, y: number);
+
+    static default: "foo";
+}
+
+export = Point;
+// @filename: index.ts
+import Point from "./point";
+
+const C = Point;
+const p = new C(1, 2);