do not emit Object.defineProperty exports (#24)

Author: guybedford

README.md

@@ -86,7 +86,7 @@ EXPORTS_SPREAD: `...` COMMENT_SPACE (IDENTIFIER | REQUIRE)
 
 EXPORTS_MEMBER: EXPORTS_DOT_ASSIGN | EXPORTS_LITERAL_COMPUTED_ASSIGN
 
-EXPORTS_DEFINE: `Object` COMMENT_SPACE `.` COMMENT_SPACE `defineProperty COMMENT_SPACE `(` EXPORTS_IDENTIFIER COMMENT_SPACE `,` COMMENT_SPACE IDENTIFIER_STRING
+ES_MODULE_DEFINE: `Object` COMMENT_SPACE `.` COMMENT_SPACE `defineProperty COMMENT_SPACE `(` COMMENT_SPACE `__esModule` COMMENT_SPACE `,` COMMENT_SPACE IDENTIFIER_STRING
 
 EXPORTS_LITERAL: MODULE_EXPORTS COMMENT_SPACE `=` COMMENT_SPACE `{` COMMENT_SPACE (EXPORTS_LITERAL_PROP | EXPORTS_SPREAD) COMMENT_SPACE `,` COMMENT_SPACE)+ `}`
 
@@ -113,7 +113,9 @@ EXPORT_STAR_LIB: `Object.keys(` IDENTIFIER$1 `).forEach(function (` IDENTIFIER$2
   `})`
 ```
 
-* The returned export names are the matched `IDENTIFIER` and `IDENTIFIER_STRING` slots for all `EXPORTS_MEMBER`, `EXPORTS_DEFINE` and `EXPORTS_LITERAL` matches.
+* The returned export names are taken to be the combination of:
+  1. `IDENTIFIER` and `IDENTIFIER_STRING` slots for all `EXPORTS_MEMBER` and `EXPORTS_LITERAL` matches.
+  2. `__esModule` if there is an `ES_MODULE_DEFINE` match.
 * The reexport specifiers are taken to be the the combination of:
   1. The `REQUIRE` matches of the last matched of either `MODULE_EXPORTS_ASSIGN` or `EXPORTS_LITERAL`.
   2. All _top-level_ `EXPORT_STAR` `REQUIRE` matches and `EXPORTS_ASSIGN` matches whose `IDENTIFIER` also matches the first `IDENTIFIER` in `EXPORT_STAR_LIB`.
@@ -125,11 +127,10 @@ EXPORT_STAR_LIB: `Object.keys(` IDENTIFIER$1 `).forEach(function (` IDENTIFIER$2
 The basic matching rules for named exports are `exports.name`, `exports['name']` or `Object.defineProperty(exports, 'name', ...)`. This matching is done without scope analysis and regardless of the expression position:
 
 ```js
-// DETECTS EXPORTS: a, b, c
+// DETECTS EXPORTS: a, b
 (function (exports) {
   exports.a = 'a'; 
   exports['b'] = 'b';
-  Object.defineProperty(exports, 'c', { value: 'c' });
 })(exports);
 ```
 
@@ -141,21 +142,32 @@ Because there is no scope analysis, the above detection may overclassify:
   exports.a = 'a';
   exports['b'] = 'b';
   if (false)
-    Object.defineProperty(exports, 'c', { value: 'c' });
+    exports.c = 'c';
 })(NOT_EXPORTS, NOT_OBJECT);
 ```
 
 It will in turn underclassify in cases where the identifiers are renamed:
 
 ```js
 // DETECTS: NO EXPORTS
-(function (e, defineProperty) {
+(function (e) {
   e.a = 'a';
   e['b'] = 'b';
-  defineProperty(e, 'c', { value: 'c' });
-})(exports, defineProperty);
+})(exports);
+```
+
+#### __esModule Detection
+
+In addition, `__esModule` is detected as an export when set by `Object.defineProperty`:
+
+```js
+// DETECTS: __esModule
+Object.defineProperty(exports, 'a', { value: 'a' });
+Object.defineProperty(exports, '__esModule', { value: true });
 ```
 
+No other named exports are detected for `defineProperty` calls in order not to trigger getters or non-enumerable properties unnecessarily.
+
 #### Exports Object Assignment
 
 A best-effort is made to detect `module.exports` object assignments, but because this is not a full parser, arbitrary expressions are not handled in the

lexer.js

@@ -278,7 +278,9 @@ function tryParseObjectDefineOrKeys (keys) {
             const exportPos = ++pos;
             if (identifier() && source.charCodeAt(pos) === ch) {
               // revert for "("
-              addExport(source.slice(exportPos, pos));
+              const expt = source.slice(exportPos, pos);
+              if (expt === '__esModule')
+                addExport(expt);
             }
           }
         }

src/lexer.c

@@ -290,7 +290,8 @@ void tryParseObjectDefineOrKeys (bool keys) {
             uint16_t* exportPos = ++pos;
             if (identifier(*pos) && *pos == ch) {
               // revert for "("
-              addExport(exportPos, pos);
+              if (pos - exportPos == 10 && str_eq10(exportPos, '_', '_', 'e', 's', 'M', 'o', 'd', 'u', 'l', 'e'))
+                addExport(exportPos, pos);
             }
           }
         }

test/_unit.js

@@ -453,10 +453,8 @@ suite('Lexer', () => {
       Object.defineProperty(module.exports, 'thing', { value: true });
       Object.defineProperty(exports, "__esModule", { value: true });
     `);
-    assert.equal(exports.length, 3);
-    assert.equal(exports[0], 'namedExport');
-    assert.equal(exports[1], 'thing');
-    assert.equal(exports[2], '__esModule');
+    assert.equal(exports.length, 1);
+    assert.equal(exports[0], '__esModule');
   });
 
   test('module assign', () => {