util: if present, fallback to `toString` using the %s formatter

This makes sure that `util.format` uses `String` to stringify an object
in case the object has an own property named `toString` with type
`function`. That way objects that do not have such function are still
inspected using `util.inspect` and the old behavior is preserved as
well.

PR-URL: https://github.com/nodejs/node/pull/27621
Refs: https://github.com/facebook/jest/issues/8443
Reviewed-By: Roman Reiss <me@silverwind.io>

1 files changed, 30 insertions, 9 deletions

diff --git a/lib/internal/util/inspect.js b/lib/internal/util/inspect.js
index 07757f3fe0..e46a18633c 100644
--- a/lib/internal/util/inspect.js
+++ b/lib/internal/util/inspect.js
@@ -93,6 +93,10 @@ const { NativeModule } = require('internal/bootstrap/loaders');
 
 let hexSlice;
 
+const builtInObjects = new Set(
+  Object.getOwnPropertyNames(global).filter((e) => /^([A-Z][a-z]+)+$/.test(e))
+);
+
 const inspectDefaultOptions = Object.seal({
   showHidden: false,
   depth: 2,
@@ -1541,16 +1545,33 @@ function formatWithOptions(inspectOptions, ...args) {
           switch (nextChar) {
             case 115: // 's'
               const tempArg = args[++a];
-              if (typeof tempArg !== 'string' &&
-                  typeof tempArg !== 'function') {
-                tempStr = inspect(tempArg, {
-                  ...inspectOptions,
-                  compact: 3,
-                  colors: false,
-                  depth: 0
-                });
+              if (typeof tempArg === 'number') {
+                tempStr = formatNumber(stylizeNoColor, tempArg);
+              // eslint-disable-next-line valid-typeof
+              } else if (typeof tempArg === 'bigint') {
+                tempStr = `${tempArg}n`;
               } else {
-                tempStr = String(tempArg);
+                let constr;
+                if (typeof tempArg !== 'object' ||
+                    tempArg === null ||
+                    typeof tempArg.toString === 'function' &&
+                     // A direct own property.
+                     (hasOwnProperty(tempArg, 'toString') ||
+                      // A direct own property on the constructor prototype in
+                      // case the constructor is not an built-in object.
+                      (constr = tempArg.constructor) &&
+                      !builtInObjects.has(constr.name) &&
+                      constr.prototype &&
+                      hasOwnProperty(constr.prototype, 'toString'))) {
+                  tempStr = String(tempArg);
+                } else {
+                  tempStr = inspect(tempArg, {
+                    ...inspectOptions,
+                    compact: 3,
+                    colors: false,
+                    depth: 0
+                  });
+                }
               }
               break;
             case 106: // 'j'