util: allow returning this from custom inspect

addaleax · addaleax · commit a60ed8917858 · 2016-08-25T07:18:12.000+02:00
If a custom inspection function returned `this`, use that value for further formatting instead of going into infinite recursion. This is particularly useful when combined with `util.inspect.custom` because returning `this` from such a method makes it easy to have an `inspect()` function that is ignored by `util.inspect` without actually having to provide an alternative for custom inspection. PR-URL: #8174 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Michaël Zasso <mic.besace@gmail.com>
diff --git a/lib/util.js b/lib/util.js
@@ -362,10 +362,15 @@ function formatValue(ctx, value, recurseTimes) {
         // Also filter out any prototype objects using the circular check.
         !(value.constructor && value.constructor.prototype === value)) {
       let ret = maybeCustomInspect.call(value, recurseTimes, ctx);
-      if (typeof ret !== 'string') {
-        ret = formatValue(ctx, ret, recurseTimes);
+
+      // If the custom inspection method returned `this`, don't go into
+      // infinite recursion.
+      if (ret !== value) {
+        if (typeof ret !== 'string') {
+          ret = formatValue(ctx, ret, recurseTimes);
+        }
+        return ret;
       }
-      return ret;
     }
   }
 
diff --git a/test/parallel/test-util-inspect.js b/test/parallel/test-util-inspect.js
@@ -567,6 +567,16 @@ assert.doesNotThrow(function() {
   );
 }
 
+{
+  // Returning `this` from a custom inspection function works.
+  assert.strictEqual(util.inspect({ a: 123, inspect() { return this; } }),
+                     '{ a: 123, inspect: [Function: inspect] }');
+
+  const subject = { a: 123, [util.inspect.custom]() { return this; } };
+  assert.strictEqual(util.inspect(subject),
+                     '{ a: 123 }');
+}
+
 // util.inspect with "colors" option should produce as many lines as without it
 function test_lines(input) {
   var count_lines = function(str) {

Original file line number	Diff line number	Diff line change
`@@ -362,10 +362,15 @@ function formatValue(ctx, value, recurseTimes) {`
`362`	`362`	`// Also filter out any prototype objects using the circular check.`
`363`	`363`	`!(value.constructor && value.constructor.prototype === value)) {`
`364`	`364`	`let ret = maybeCustomInspect.call(value, recurseTimes, ctx);`
`365`		`- if (typeof ret !== 'string') {`
`366`		`- ret = formatValue(ctx, ret, recurseTimes);`
	`365`	`+`
	`366`	+ // If the custom inspection method returned `this`, don't go into
	`367`	`+ // infinite recursion.`
	`368`	`+ if (ret !== value) {`
	`369`	`+ if (typeof ret !== 'string') {`
	`370`	`+ ret = formatValue(ctx, ret, recurseTimes);`
	`371`	`+ }`
	`372`	`+ return ret;`
`367`	`373`	`}`
`368`		`- return ret;`
`369`	`374`	`}`
`370`	`375`	`}`
`371`	`376`