util: add inspection getter option

Currently it is not possible to inspect getters. To prevent any side
effects this should not become a default but under lots of
circumstances it would still be useful to inspect getters. This way
it is possible to actively opt into inspecting those.

PR-URL: nodejs#24852
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

doc/api/util.md

@@ -389,6 +389,9 @@ stream.write('With ES6');
 <!-- YAML
 added: v0.3.0
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/24852
+    description: The `getters` option is supported now.
   - version: v11.4.0
     pr-url: https://github.com/nodejs/node/pull/24326
     description: The `depth` default changed back to `2`.
@@ -468,6 +471,11 @@ changes:
     of an object and Set and Map entries will be sorted in the returned string.
     If set to `true` the [default sort][] is going to be used. If set to a
     function, it is used as a [compare function][].
+  * `getters` {boolean|string} If set to `true`, getters are going to be
+    inspected as well. If set to `'get'` only getters without setter are going
+    to be inspected. If set to `'set'` only getters having a corresponding
+    setter are going to be inspected. This might cause side effects depending on
+    the getter function. **Default:** `false`.
 * Returns: {string} The representation of passed object
 
 The `util.inspect()` method returns a string representation of `object` that is

lib/internal/util/inspect.js

@@ -99,7 +99,8 @@ const inspectDefaultOptions = Object.seal({
   maxArrayLength: 100,
   breakLength: 60,
   compact: true,
-  sorted: false
+  sorted: false,
+  getters: false
 });
 
 const kObjectType = 0;
@@ -167,7 +168,8 @@ function inspect(value, opts) {
     maxArrayLength: inspectDefaultOptions.maxArrayLength,
     breakLength: inspectDefaultOptions.breakLength,
     compact: inspectDefaultOptions.compact,
-    sorted: inspectDefaultOptions.sorted
+    sorted: inspectDefaultOptions.sorted,
+    getters: inspectDefaultOptions.getters
   };
   if (arguments.length > 1) {
     // Legacy...
@@ -1131,10 +1133,30 @@ function formatProperty(ctx, value, recurseTimes, key, type) {
     }
     ctx.indentationLvl -= diff;
   } else if (desc.get !== undefined) {
-    if (desc.set !== undefined) {
-      str = ctx.stylize('[Getter/Setter]', 'special');
+    const label = desc.set !== undefined ? 'Getter/Setter' : 'Getter';
+    const s = ctx.stylize;
+    const sp = 'special';
+    if (ctx.getters && (ctx.getters === true ||
+          ctx.getters === 'get' && desc.set === undefined ||
+          ctx.getters === 'set' && desc.set !== undefined)) {
+      try {
+        const tmp = value[key];
+        ctx.indentationLvl += 2;
+        if (tmp === null) {
+          str = `${s(`[${label}:`, sp)} ${s('null', 'null')}${s(']', sp)}`;
+        } else if (typeof tmp === 'object') {
+          str = `${s(`[${label}]`, sp)} ${formatValue(ctx, tmp, recurseTimes)}`;
+        } else {
+          const primitive = formatPrimitive(s, tmp, ctx);
+          str = `${s(`[${label}:`, sp)} ${primitive}${s(']', sp)}`;
+        }
+        ctx.indentationLvl -= 2;
+      } catch (err) {
+        const message = `<Inspection threw (${err.message})>`;
+        str = `${s(`[${label}:`, sp)} ${message}${s(']', sp)}`;
+      }
     } else {
-      str = ctx.stylize('[Getter]', 'special');
+      str = ctx.stylize(`[${label}]`, sp);
     }
   } else if (desc.set !== undefined) {
     str = ctx.stylize('[Setter]', 'special');

test/parallel/test-util-inspect.js

@@ -1764,3 +1764,36 @@ assert.strictEqual(
   });
   assert.strictEqual(util.inspect(obj), '[Set: null prototype] { 1, 2 }');
 }
+
+// Check the getter option.
+{
+  let foo = 1;
+  const get = { get foo() { return foo; } };
+  const getset = {
+    get foo() { return foo; },
+    set foo(val) { foo = val; },
+    get inc() { return ++foo; }
+  };
+  const thrower = { get foo() { throw new Error('Oops'); } };
+  assert.strictEqual(
+    inspect(get, { getters: true, colors: true }),
+    '{ foo: \u001b[36m[Getter:\u001b[39m ' +
+      '\u001b[33m1\u001b[39m\u001b[36m]\u001b[39m }');
+  assert.strictEqual(
+    inspect(thrower, { getters: true }),
+    '{ foo: [Getter: <Inspection threw (Oops)>] }');
+  assert.strictEqual(
+    inspect(getset, { getters: true }),
+    '{ foo: [Getter/Setter: 1], inc: [Getter: 2] }');
+  assert.strictEqual(
+    inspect(getset, { getters: 'get' }),
+    '{ foo: [Getter/Setter], inc: [Getter: 3] }');
+  assert.strictEqual(
+    inspect(getset, { getters: 'set' }),
+    '{ foo: [Getter/Setter: 3], inc: [Getter] }');
+  getset.foo = new Set([[{ a: true }, 2, {}], 'foobar', { x: 1 }]);
+  assert.strictEqual(
+    inspect(getset, { getters: true }),
+    '{ foo: [Getter/Setter] Set { [ [Object], 2, {} ], ' +
+      "'foobar', { x: 1 } },\n  inc: [Getter: NaN] }");
+}