util: add subclass and null prototype support for errors in inspect

This adds support to visualize the difference between errors with
null prototype or subclassed errors. This has a couple safeguards
to be sure that the output is not intrusive.

PR-URL: https://github.com/nodejs/node/pull/26923
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

lib/internal/util/inspect.js

@@ -666,25 +666,9 @@ function formatRaw(ctx, value, recurseTimes, typedArray) {
         return ctx.stylize(base, 'date');
       }
     } else if (isError(value)) {
-      // Make error with message first say the error.
+      base = formatError(value, constructor, tag, ctx);
-      base = formatError(value);
-      // Wrap the error in brackets in case it has no stack trace.
-      const stackStart = base.indexOf('\n    at');
-      if (stackStart === -1) {
-        base = `[${base}]`;
-      }
-      // The message and the stack have to be indented as well!
-      if (ctx.indentationLvl !== 0) {
-        const indentation = ' '.repeat(ctx.indentationLvl);
-        base = formatError(value).replace(/\n/g, `\n${indentation}`);
-      }
       if (keys.length === 0)
         return base;
-
-      if (ctx.compact === false && stackStart !== -1) {
-        braces[0] += `${base.slice(stackStart)}`;
-        base = `[${base.slice(0, stackStart)}]`;
-      }
     } else if (isAnyArrayBuffer(value)) {
       // Fast path for ArrayBuffer and SharedArrayBuffer.
       // Can't do the same for DataView because it has a non-primitive
@@ -844,6 +828,52 @@ function formatRaw(ctx, value, recurseTimes, typedArray) {
   return res;
 }
 
+function formatError(err, constructor, tag, ctx) {
+  // TODO(BridgeAR): Always show the error code if present.
+  let stack = err.stack || errorToString(err);
+
+  // A stack trace may contain arbitrary data. Only manipulate the output
+  // for "regular errors" (errors that "look normal") for now.
+  const name = err.name || 'Error';
+  let len = name.length;
+  if (constructor === null ||
+      name.endsWith('Error') &&
+      stack.startsWith(name) &&
+      (stack.length === len || stack[len] === ':' || stack[len] === '\n')) {
+    let fallback = 'Error';
+    if (constructor === null) {
+      const start = stack.match(/^([A-Z][a-z_ A-Z0-9[\]()-]+)(?::|\n {4}at)/) ||
+        stack.match(/^([a-z_A-Z0-9-]*Error)$/);
+      fallback = start && start[1] || '';
+      len = fallback.length;
+      fallback = fallback || 'Error';
+    }
+    const prefix = getPrefix(constructor, tag, fallback).slice(0, -1);
+    if (name !== prefix) {
+      if (prefix.includes(name)) {
+        if (len === 0) {
+          stack = `${prefix}: ${stack}`;
+        } else {
+          stack = `${prefix}${stack.slice(len)}`;
+        }
+      } else {
+        stack = `${prefix} [${name}]${stack.slice(len)}`;
+      }
+    }
+  }
+  // Wrap the error in brackets in case it has no stack trace.
+  const stackStart = stack.indexOf('\n    at');
+  if (stackStart === -1) {
+    stack = `[${stack}]`;
+  }
+  // The message and the stack have to be indented as well!
+  if (ctx.indentationLvl !== 0) {
+    const indentation = ' '.repeat(ctx.indentationLvl);
+    stack = stack.replace(/\n/g, `\n${indentation}`);
+  }
+  return stack;
+}
+
 function groupArrayElements(ctx, output) {
   let totalLength = 0;
   let maxLength = 0;
@@ -991,11 +1021,6 @@ function formatPrimitive(fn, value, ctx) {
   return fn(value.toString(), 'symbol');
 }
 
-function formatError(value) {
-  // TODO(BridgeAR): Always show the error code if present.
-  return value.stack || errorToString(value);
-}
-
 function formatNamespaceObject(ctx, value, recurseTimes, keys) {
   const output = new Array(keys.length);
   for (var i = 0; i < keys.length; i++) {

test/parallel/test-util-inspect.js

@@ -1663,6 +1663,70 @@ assert.strictEqual(util.inspect('"\''), '`"\'`');
 // eslint-disable-next-line no-template-curly-in-string
 assert.strictEqual(util.inspect('"\'${a}'), "'\"\\'${a}'");
 
+// Errors should visualize as much information as possible.
+// If the name is not included in the stack, visualize it as well.
+[
+  [class Foo extends TypeError {}, 'test'],
+  [class Foo extends TypeError {}, undefined],
+  [class BarError extends Error {}, 'test'],
+  [class BazError extends Error {
+    get name() {
+      return 'BazError';
+    }
+  }, undefined]
+].forEach(([Class, message, messages], i) => {
+  console.log('Test %i', i);
+  const foo = new Class(message);
+  const name = foo.name;
+  const extra = Class.name.includes('Error') ? '' : ` [${foo.name}]`;
+  assert(
+    util.inspect(foo).startsWith(
+      `${Class.name}${extra}${message ? `: ${message}` : '\n'}`),
+    util.inspect(foo)
+  );
+  Object.defineProperty(foo, Symbol.toStringTag, {
+    value: 'WOW',
+    writable: true,
+    configurable: true
+  });
+  const stack = foo.stack;
+  foo.stack = 'This is a stack';
+  assert.strictEqual(
+    util.inspect(foo),
+    '[This is a stack]'
+  );
+  foo.stack = stack;
+  assert(
+    util.inspect(foo).startsWith(
+      `${Class.name} [WOW]${extra}${message ? `: ${message}` : '\n'}`),
+    util.inspect(foo)
+  );
+  Object.setPrototypeOf(foo, null);
+  assert(
+    util.inspect(foo).startsWith(
+      `[${name}: null prototype] [WOW]${message ? `: ${message}` : '\n'}`
+    ),
+    util.inspect(foo)
+  );
+  foo.bar = true;
+  delete foo[Symbol.toStringTag];
+  assert(
+    util.inspect(foo).startsWith(
+      `{ [${name}: null prototype]${message ? `: ${message}` : '\n'}`),
+    util.inspect(foo)
+  );
+  foo.stack = 'This is a stack';
+  assert.strictEqual(
+    util.inspect(foo),
+    '{ [[Error: null prototype]: This is a stack] bar: true }'
+  );
+  foo.stack = stack.split('\n')[0];
+  assert.strictEqual(
+    util.inspect(foo),
+    `{ [[${name}: null prototype]${message ? `: ${message}` : ''}] bar: true }`
+  );
+});
+
 // Verify that throwing in valueOf and toString still produces nice results.
 [
   [new String(55), "[String: '55']"],