util: improve inspect performance

This improves a slow code part in `util.inspect` by directly
retrieving the `Symbol.toStringTag` and by optimizing some code
paths.

PR-URL: https://github.com/nodejs/node/pull/20009
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Yuta Hiroto <hello@hiroppy.me>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

lib/internal/util.js

@@ -252,43 +252,6 @@ function getSystemErrorName(err) {
   return entry ? entry[0] : `Unknown system error ${err}`;
 }
 
-// getConstructorOf is wrapped into this to save iterations
-function getIdentificationOf(obj) {
-  const original = obj;
-  let constructor;
-  let tag;
-
-  while (obj) {
-    if (constructor === undefined) {
-      const desc = Object.getOwnPropertyDescriptor(obj, 'constructor');
-      if (desc !== undefined &&
-          typeof desc.value === 'function' &&
-          desc.value.name !== '')
-        constructor = desc.value.name;
-    }
-
-    if (tag === undefined) {
-      const desc = Object.getOwnPropertyDescriptor(obj, Symbol.toStringTag);
-      if (desc !== undefined) {
-        if (typeof desc.value === 'string') {
-          tag = desc.value;
-        } else if (desc.get !== undefined) {
-          tag = desc.get.call(original);
-          if (typeof tag !== 'string')
-            tag = undefined;
-        }
-      }
-    }
-
-    if (constructor !== undefined && tag !== undefined)
-      break;
-
-    obj = Object.getPrototypeOf(obj);
-  }
-
-  return { constructor, tag };
-}
-
 const kCustomPromisifiedSymbol = Symbol('util.promisify.custom');
 const kCustomPromisifyArgsSymbol = Symbol('customPromisifyArgs');
 
@@ -431,7 +394,6 @@ module.exports = {
   filterDuplicateStrings,
   getConstructorOf,
   getSystemErrorName,
-  getIdentificationOf,
   isError,
   isInsideNodeModules,
   join,

lib/util.js

@@ -72,7 +72,6 @@ const {
   customInspectSymbol,
   deprecate,
   getSystemErrorName: internalErrorName,
-  getIdentificationOf,
   isError,
   promisify,
   join,
@@ -396,6 +395,35 @@ function stylizeNoColor(str, styleType) {
   return str;
 }
 
+function getConstructorName(obj) {
+  while (obj) {
+    const descriptor = Object.getOwnPropertyDescriptor(obj, 'constructor');
+    if (descriptor !== undefined &&
+        typeof descriptor.value === 'function' &&
+        descriptor.value.name !== '') {
+      return descriptor.value.name;
+    }
+
+    obj = Object.getPrototypeOf(obj);
+  }
+
+  return '';
+}
+
+function getPrefix(constructor, tag) {
+  if (constructor !== '') {
+    if (tag !== '' && constructor !== tag) {
+      return `${constructor} [${tag}] `;
+    }
+    return `${constructor} `;
+  }
+
+  if (tag !== '')
+    return `[${tag}] `;
+
+  return '';
+}
+
 function formatValue(ctx, value, recurseTimes, ln) {
   // Primitive types cannot have properties
   if (typeof value !== 'object' && typeof value !== 'function') {
@@ -475,15 +503,10 @@ function formatValue(ctx, value, recurseTimes, ln) {
 
   const keyLength = keys.length + symbols.length;
 
-  const { constructor, tag } = getIdentificationOf(value);
+  const constructor = getConstructorName(value);
-  let prefix = '';
+  let tag = value[Symbol.toStringTag];
-  if (constructor && tag && constructor !== tag)
+  if (typeof tag !== 'string')
-    prefix = `${constructor} [${tag}] `;
+    tag = '';
-  else if (constructor)
-    prefix = `${constructor} `;
-  else if (tag)
-    prefix = `[${tag}] `;
-
   let base = '';
   let formatter = formatObject;
   let braces;
@@ -496,22 +519,25 @@ function formatValue(ctx, value, recurseTimes, ln) {
     noIterator = false;
     if (Array.isArray(value)) {
       // Only set the constructor for non ordinary ("Array [...]") arrays.
+      const prefix = getPrefix(constructor, tag);
       braces = [`${prefix === 'Array ' ? '' : prefix}[`, ']'];
       if (value.length === 0 && keyLength === 0)
         return `${braces[0]}]`;
       formatter = formatArray;
     } else if (isSet(value)) {
+      const prefix = getPrefix(constructor, tag);
       if (value.size === 0 && keyLength === 0)
         return `${prefix}{}`;
       braces = [`${prefix}{`, '}'];
       formatter = formatSet;
     } else if (isMap(value)) {
+      const prefix = getPrefix(constructor, tag);
       if (value.size === 0 && keyLength === 0)
         return `${prefix}{}`;
       braces = [`${prefix}{`, '}'];
       formatter = formatMap;
     } else if (isTypedArray(value)) {
-      braces = [`${prefix}[`, ']'];
+      braces = [`${getPrefix(constructor, tag)}[`, ']'];
       formatter = formatTypedArray;
     } else if (isMapIterator(value)) {
       braces = [`[${tag}] {`, '}'];
@@ -543,11 +569,16 @@ function formatValue(ctx, value, recurseTimes, ln) {
   }
   if (noIterator) {
     braces = ['{', '}'];
-    if (prefix === 'Object ') {
+    if (constructor === 'Object') {
       if (isArgumentsObject(value)) {
         braces[0] = '[Arguments] {';
         if (keyLength === 0)
           return '[Arguments] {}';
+      } else if (tag !== '') {
+        braces[0] = `${getPrefix(constructor, tag)}{`;
+        if (keyLength === 0) {
+          return `${braces[0]}}`;
+        }
       } else if (keyLength === 0) {
         return '{}';
       }
@@ -579,27 +610,28 @@ function formatValue(ctx, value, recurseTimes, ln) {
       // Fast path for ArrayBuffer and SharedArrayBuffer.
       // Can't do the same for DataView because it has a non-primitive
       // .buffer property that we need to recurse for.
+      const prefix = getPrefix(constructor, tag);
       if (keyLength === 0)
         return prefix +
               `{ byteLength: ${formatNumber(ctx.stylize, value.byteLength)} }`;
       braces[0] = `${prefix}{`;
       keys.unshift('byteLength');
     } else if (isDataView(value)) {
-      braces[0] = `${prefix}{`;
+      braces[0] = `${getPrefix(constructor, tag)}{`;
       // .buffer goes last, it's not a primitive like the others.
       keys.unshift('byteLength', 'byteOffset', 'buffer');
     } else if (isPromise(value)) {
-      braces[0] = `${prefix}{`;
+      braces[0] = `${getPrefix(constructor, tag)}{`;
       formatter = formatPromise;
     } else if (isWeakSet(value)) {
-      braces[0] = `${prefix}{`;
+      braces[0] = `${getPrefix(constructor, tag)}{`;
       if (ctx.showHidden) {
         formatter = formatWeakSet;
       } else {
         extra = '[items unknown]';
       }
     } else if (isWeakMap(value)) {
-      braces[0] = `${prefix}{`;
+      braces[0] = `${getPrefix(constructor, tag)}{`;
       if (ctx.showHidden) {
         formatter = formatWeakMap;
       } else {
@@ -638,9 +670,9 @@ function formatValue(ctx, value, recurseTimes, ln) {
       } else if (keyLength === 0) {
         if (isExternal(value))
           return ctx.stylize('[External]', 'special');
-        return `${prefix}{}`;
+        return `${getPrefix(constructor, tag)}{}`;
       } else {
-        braces[0] = `${prefix}{`;
+        braces[0] = `${getPrefix(constructor, tag)}{`;
       }
     }
   }
@@ -675,8 +707,8 @@ function formatNumber(fn, value) {
 function formatPrimitive(fn, value, ctx) {
   if (typeof value === 'string') {
     if (ctx.compact === false &&
-      value.length > MIN_LINE_LENGTH &&
+      ctx.indentationLvl + value.length > ctx.breakLength &&
-      ctx.indentationLvl + value.length > ctx.breakLength) {
+      value.length > MIN_LINE_LENGTH) {
       // eslint-disable-next-line max-len
       const minLineLength = Math.max(ctx.breakLength - ctx.indentationLvl, MIN_LINE_LENGTH);
       // eslint-disable-next-line max-len
@@ -695,9 +727,9 @@ function formatPrimitive(fn, value, ctx) {
         // eslint-disable-next-line max-len, node-core/no-unescaped-regexp-dot
         readableRegExps[divisor] = new RegExp(`(.|\\n){1,${divisor}}(\\s|$)|(\\n|.)+?(\\s|$)`, 'gm');
       }
-      const indent = ' '.repeat(ctx.indentationLvl);
       const matches = value.match(readableRegExps[divisor]);
       if (matches.length > 1) {
+        const indent = ' '.repeat(ctx.indentationLvl);
         res += `${fn(strEscape(matches[0]), 'string')} +\n`;
         for (var i = 1; i < matches.length - 1; i++) {
           res += `${indent}  ${fn(strEscape(matches[i]), 'string')} +\n`;