module: do not warn when accessing __esModule of unfinished exports

Since this property access is performed by generated code, and not used for accessing the actual exports of a module (and because transpilers generally define it as the first key of `module.exports` when it *is* present), it should be okay to allow it. Refs: #29935Fixes: #33046 PR-URL: #33048 Reviewed-By: Guy Bedford <[email protected]> Reviewed-By: James M Snell <[email protected]> Reviewed-By: Zeyu Yang <[email protected]>

Author: addaleax

lib/internal/modules/cjs/loader.js

@@ -824,13 +824,16 @@ function emitCircularRequireWarning(prop){
 // warns when non-existend properties are accessed.
 constCircularRequirePrototypeWarningProxy=newProxy({},{
 get(target,prop){
-if(propintarget)returntarget[prop];
+// Allow __esModule access in any case because it is used in the output
+// of transpiled code to determine whether something comes from an
+// ES module, and is not used as a regular key of `module.exports`.
+if(propintarget||prop==='__esModule')returntarget[prop];
 emitCircularRequireWarning(prop);
 returnundefined;
 },
 
 getOwnPropertyDescriptor(target,prop){
-if(ObjectPrototypeHasOwnProperty(target,prop))
+if(ObjectPrototypeHasOwnProperty(target,prop)||prop==='__esModule')
 returnObjectGetOwnPropertyDescriptor(target,prop);
 emitCircularRequireWarning(prop);
 returnundefined;

test/fixtures/cycles/warning-esm-half-transpiled-a.js

@@ -0,0 +1 @@
+require('./warning-esm-half-transpiled-b.js');

test/fixtures/cycles/warning-esm-half-transpiled-b.js

@@ -0,0 +1,2 @@
+consta=require('./warning-esm-half-transpiled-a.js');
+a.__esModule;

test/parallel/test-module-circular-dependency-warning.js

@@ -31,3 +31,10 @@ assert.strictEqual(Object.getPrototypeOf(classExport).name, 'Parent');
 constesmTranspiledExport=
 require(fixtures.path('cycles','warning-esm-transpiled-a.js'));
 assert.strictEqual(esmTranspiledExport.__esModule,true);
+
+// If module.exports.__esModule is being accessed but is not present, e.g.
+// because only the one of the files is a transpiled ES module, no warning
+// should be emitted.
+consthalfTranspiledExport=
+require(fixtures.path('cycles','warning-esm-half-transpiled-a.js'));
+assert.strictEqual(halfTranspiledExport.__esModule,undefined);