util: runtime deprecate promisify-ing a function returning a Promise

nodejs · Sep 16, 2023 · 2fb3d51 · 2fb3d51
1 parent 71b90fa
commit 2fb3d51
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Showing 2 changed files with 19 additions and 2 deletions.
diff --git a/lib/internal/util.js b/lib/internal/util.js
@@ -63,7 +63,7 @@ const {
   sleep: _sleep,
   toUSVString: _toUSVString,
 } = internalBinding('util');
-const { isNativeError } = internalBinding('types');
+const { isNativeError, isPromise } = internalBinding('types');
 const { getOptionValue } = require('internal/options');
 
 const noCrypto = !process.versions.openssl;
@@ -409,7 +409,9 @@ function promisify(original) {
           resolve(values[0]);
         }
       });
-      ReflectApply(original, this, args);
+      if (isPromise(ReflectApply(original, this, args))) {
+        process.emitWarning('Calling promisify on a function that returns a Promise is likely a mistake.');
+      }
     });
   }
 

diff --git a/test/parallel/test-util-promisify.js b/test/parallel/test-util-promisify.js
@@ -7,6 +7,21 @@ const vm = require('vm');
 const { promisify } = require('util');
 const { customPromisifyArgs } = require('internal/util');
 
+{
+  const warningHandler = common.mustNotCall();
+  process.on('warning', warningHandler);
+  function foo() {}
+  foo.constructor = (async () => {}).constructor;
+  promisify(foo);
+  process.off('warning', warningHandler);
+}
+
+common.expectWarning('Warning', 'Calling promisify on a function that returns a Promise is likely a mistake.');
+promisify(async (callback) => { callback(); })().then(common.mustCall(() => {
+  common.expectWarning('Warning', 'Calling promisify on a function that returns a Promise is likely a mistake.');
+  promisify(async () => {})().then(common.mustNotCall());
+}));
+
 const stat = promisify(fs.stat);
 
 {