Look up exports whose names start with "__" by their escaped key

TypeScript keys a symbol table entry whose name starts with `__` with an
extra `_` (`__x` is stored as `___x`; `symbolName` removes it). Native ESM
link checking looked an import up by its own spelling, so a program that
imports such an export compiled to Node's startup SyntaxError:

    // dep.ts
    export const __x = 1;
    // main.ts
    import { __x } from "./dep.ts"; // The requested module './dep.ts'
                                    // does not provide an export named '__x'

`escapedSymbolName`, the inverse of `symbolName`, gives a name's table key.
Link checking, external type lookups, CommonJS export lookups and the
`this` check of ES module exports now look names up through it. `Object.keys`
over a module namespace skipped every key starting with `__` to drop
TypeScript's internal names, so it also dropped these exports; it now
skips only internal names and lists exports by their own names.

Closes #1582.

Co-authored-by: thekevinbrown <1531750+thekevinbrown@users.noreply.github.com>

packages/compiler/src/frontend/lowering/cjs-exports-object.ts

@@ -381,7 +381,7 @@ function esModuleExportIgnoresThis(
   depth: number,
 ): boolean {
   const moduleSym = lowerer.checker.getSymbolAtLocation(sf);
-  const exported = moduleSym?.getExports().get(name as ts.__String);
+  const exported = moduleSym?.getExports().get(ts.escapedSymbolName(name));
   if (exported !== undefined) {
     const target =
       exported.flags & ts.SymbolFlags.Alias ? lowerer.checker.getAliasedSymbol(exported) : exported;

packages/compiler/src/frontend/lowering/lower-calls.ts

@@ -8777,11 +8777,13 @@ function lowerObjectStaticCall(
       const moduleSymbol = source ? lowerer.checker.getSymbolAtLocation(source) : undefined;
       const names: string[] = [];
       moduleSymbol?.getExports().forEach((symbol, key) => {
+        // Internal names (`__export`) start with `__`; an exported name that
+        // does is keyed with an extra `_` (escapedSymbolName).
         const name = String(key);
-        if (name.startsWith("__") || name === "export=") return;
+        if ((name.startsWith("__") && !name.startsWith("___")) || name === "export=") return;
         const target =
           symbol.flags & ts.SymbolFlags.Alias ? lowerer.checker.getAliasedSymbol(symbol) : symbol;
-        if (target.flags & ts.SymbolFlags.Value) names.push(name);
+        if (target.flags & ts.SymbolFlags.Value) names.push(ts.symbolName(symbol));
       });
       names.sort();
       const loc = locOf(call);

packages/compiler/src/frontend/lowering/lowerer.ts

@@ -4219,7 +4219,7 @@ export class Lowerer {
     // exact mappings, while star exports resolve to the mapped declaration
     // owner through externalTypeSpecifiersByFile.
     const moduleSymbol = this.checker.getSymbolAtLocation(sf);
-    const exported = moduleSymbol?.getExports().get(exportName as ts.__String);
+    const exported = moduleSymbol?.getExports().get(ts.escapedSymbolName(exportName));
     return this.externalTypeSpecifierOfSymbol(exported, seenSymbols, seenExports);
   }
 
@@ -4362,7 +4362,7 @@ export class Lowerer {
   cjsModuleExportSymbol(sf: ts.SourceFile, name: string): ts.Symbol | undefined {
     const moduleSym = this.checker.getSymbolAtLocation(sf);
     const exports = moduleSym?.getExports();
-    const direct = exports?.get(name as ts.__String);
+    const direct = exports?.get(ts.escapedSymbolName(name));
     if (direct) return direct;
     // tsgo represents `module.exports = { ... }` as one `export=` symbol
     // and does not duplicate the object literal's properties into the

packages/compiler/src/frontend/program.ts

@@ -6437,7 +6437,7 @@ function analyzeEsmNamedImportLinks(
     const nextSeen = new Set(seenModules);
     nextSeen.add(dep);
     const module = checker.getSymbolAtLocation(dep);
-    const exported = module?.getExports().get(name as ts.__String);
+    const exported = module?.getExports().get(ts.escapedSymbolName(name));
     if (exported !== undefined) {
       let resolved = exported;
       const seenSymbols = new Set<ts.Symbol>();

packages/compiler/src/frontend/ts7/semantic-model.test.ts

@@ -28,6 +28,7 @@ import {
   SemanticSnapshot,
   SemanticType,
   symbolNameOf,
+  escapedSymbolName,
 } from "./semantic-model.js";
 import type { __String } from "./ast-types.js";
 import {
@@ -313,6 +314,11 @@ test("symbol tables keep escaped keys, display names, canonical context and cach
   const exports = parent.getExports();
   expect(symbolNameOf(members.get("___x" as __String))).toBe("__x");
   expect(symbolNameOf(exports.get("__x" as __String))).toBe("__x");
+  // A name that starts with `__` is keyed with an extra `_`.
+  expect(symbolNameOf(members.get(escapedSymbolName("__x")))).toBe("__x");
+  expect(escapedSymbolName("x")).toBe("x");
+  expect(escapedSymbolName("_x")).toBe("_x");
+  expect(escapedSymbolName("___y")).toBe("____y");
   expect(parent.getMembers()).toBe(members);
   expect(parent.getExports()).toBe(exports);
   expect(parent.getParent()).toBe(first.symbol(symbol(2)));

packages/compiler/src/frontend/ts7/semantic-model.ts

@@ -454,6 +454,12 @@ export function symbolName(symbol: SemanticSymbol): string {
   return name.startsWith("___") ? name.slice(1) : name;
 }
 
+/** The key of the name `name` in a symbol table (`getExports()`, `getMembers()`): the name, with
+ * an extra `_` when it starts with `__`. The inverse of `symbolName`. */
+export function escapedSymbolName(name: string): __String {
+  return (name.startsWith("__") ? `_${name}` : name) as __String;
+}
+
 /** `symbolName(symbol)`, or undefined without a symbol. */
 export function symbolNameOf(symbol: SemanticSymbol | null | undefined): string | undefined {
   return symbol === undefined || symbol === null ? undefined : symbolName(symbol);

packages/compiler/src/frontend/ts7/semantic-types.ts

@@ -30,7 +30,7 @@ export type {
   SemanticSignature as Signature,
   SemanticSymbol as Symbol,
 } from "./semantic-model.js";
-export { symbolName, symbolNameOf } from "./semantic-model.js";
+export { escapedSymbolName, symbolName, symbolNameOf } from "./semantic-model.js";
 export type {
   SemanticIndexInfo as IndexInfo,
   SemanticTypePredicate as TypePredicate,

packages/compiler/test/ts7/baselines/order-parity/tests/corpus/7306-dunder-exports/main.ts.json

@@ -0,0 +1,10 @@
+{
+ "order": [
+  "<repo>/tests/corpus/7306-dunder-exports/dep.ts",
+  "<repo>/tests/corpus/7306-dunder-exports/star.ts",
+  "<repo>/tests/corpus/7306-dunder-exports/facade.ts",
+  "<repo>/tests/corpus/7306-dunder-exports/table.cjs",
+  "<repo>/tests/corpus/7306-dunder-exports/main.ts"
+ ],
+ "diags": []
+}

tests/corpus/7306-dunder-exports/dep.ts

@@ -0,0 +1,19 @@
+export const __x = 1;
+export const ___y = "three";
+export let __count = 0;
+export function __bump(): number {
+  __count++;
+  return __count;
+}
+export class __Point {
+  a: number;
+  b: number;
+  constructor(a: number, b: number) {
+    this.a = a;
+    this.b = b;
+  }
+  sum(): number {
+    return this.a + this.b;
+  }
+}
+export const plain = "plain";

tests/corpus/7306-dunder-exports/facade.ts

@@ -0,0 +1,2 @@
+export { __x, __x as __alias, ___y as renamed } from "./dep.ts";
+export * from "./star.ts";

tests/corpus/7306-dunder-exports/main.ts

@@ -0,0 +1,20 @@
+// Exports whose names start with "__": named imports of a const, a function,
+// a class and a live let, a name with three underscores, aliased re-exports,
+// names reached through `export *`, namespace member reads and keys, and
+// CommonJS exports read through require.
+import { __x, ___y, __count, __bump, __Point, plain } from "./dep.ts";
+import { __alias, renamed, __starred, __twice } from "./facade.ts";
+import * as facade from "./facade.ts";
+import * as depNs from "./dep.ts";
+import { createRequire } from "node:module";
+
+console.log(__x, ___y, plain);
+console.log(__count, __bump(), __bump(), __count);
+console.log(new __Point(2, 3).sum());
+console.log(__alias, renamed, __starred, __twice(21));
+console.log(facade.__x, facade.__starred, facade.__twice(2));
+console.log(Object.keys(depNs).join(","));
+
+const require = createRequire(import.meta.url);
+const table = require("./table.cjs");
+console.log(table.__a, table.__hello("dunder"), table.b);

tests/corpus/7306-dunder-exports/star.ts

@@ -0,0 +1,4 @@
+export const __starred = "from export *";
+export function __twice(n: number): number {
+  return n * 2;
+}

tests/corpus/7306-dunder-exports/table.cjs

@@ -0,0 +1,5 @@
+exports.__a = 10;
+exports.__hello = function (name) {
+  return "hello " + name;
+};
+exports.b = 20;

tests/harness/corpus-costs/7306-dunder-exports/main.ts.json

@@ -0,0 +1 @@
+{ "plain": 2400, "san": 3600 }