util: add util.inspect compact option

The current default formatting is not ideal and this improves
the situation by formatting the output more intuitiv.

1) All object keys are now indented by 2 characters instead of
   sometimes 2 and sometimes 3 characters.
2) Each object key will now use an individual line instead of
   sharing a line potentially with multiple object keys.
3) Long strings will now be split into multiple lines in case
   they exceed the "lineBreak" option length (including the
   current indentation).
4) Opening braces are now directly behind a object property
   instead of using a new line.
5) Switch inspect "base" order. In case the compact option is set
   to `false`, inspect will now print
     "[Function: foo] {\n  property: 'data'\n}"
   instead of
     "{ [Function: foo]\n  property: 'data'\n}".

Backport-PR-URL: #19230
PR-URL: #17576
Reviewed-By: Anna Henningsen <anna@addaleax.net>

doc/api/util.md

@@ -316,6 +316,9 @@ stream.write('With ES6');
 <!-- YAML
 added: v0.3.0
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/REPLACEME
+    description: The `compact` option is supported now.
   - version: v6.6.0
     pr-url: https://github.com/nodejs/node/pull/8174
     description: Custom inspection functions can now return `this`.
@@ -353,6 +356,13 @@ changes:
   * `breakLength` {number} The length at which an object's keys are split
     across multiple lines. Set to `Infinity` to format an object as a single
     line. Defaults to 60 for legacy compatibility.
+  * `compact` {boolean} Setting this to `false` changes the default indentation
+    to use a line break for each object key instead of lining up multiple
+    properties in one line. It will also break text that is above the
+    `breakLength` size into smaller and better readable chunks and indents
+    objects the same as arrays. Note that no text will be reduced below 16
+    characters, no matter the `breakLength` size. For more information, see the
+    example below. Defaults to `true`.
 
 The `util.inspect()` method returns a string representation of `object` that is
 primarily useful for debugging. Additional `options` may be passed that alter
@@ -370,6 +380,63 @@ Values may supply their own custom `inspect(depth, opts)` functions, when
 called these receive the current `depth` in the recursive inspection, as well as
 the options object passed to `util.inspect()`.
 
+The following example highlights the difference with the `compact` option:
+
+```js
+const util = require('util');
+
+const o = {
+  a: [1, 2, [[
+    'Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do ' +
+      'eiusmod tempor incididunt ut labore et dolore magna aliqua.',
+    'test',
+    'foo']], 4],
+  b: new Map([['za', 1], ['zb', 'test']])
+};
+console.log(util.inspect(o, { compact: true, depth: 5, breakLength: 80 }));
+
+// This will print
+
+// { a:
+//   [ 1,
+//     2,
+//     [ [ 'Lorem ipsum dolor sit amet, consectetur [...]', // A long line
+//           'test',
+//           'foo' ] ],
+//     4 ],
+//   b: Map { 'za' => 1, 'zb' => 'test' } }
+
+// Setting `compact` to false changes the output to be more reader friendly.
+console.log(util.inspect(o, { compact: false, depth: 5, breakLength: 80 }));
+
+// {
+//   a: [
+//     1,
+//     2,
+//     [
+//       [
+//         'Lorem ipsum dolor sit amet, consectetur ' +
+//           'adipiscing elit, sed do eiusmod tempor ' +
+//           'incididunt ut labore et dolore magna ' +
+//           'aliqua.,
+//         'test',
+//         'foo'
+//       ]
+//     ],
+//     4
+//   ],
+//   b: Map {
+//     'za' => 1,
+//     'zb' => 'test'
+//   }
+// }
+
+// Setting `breakLength` to e.g. 150 will print the "Lorem ipsum" text in a
+// single line.
+// Reducing the `breakLength` will split the "Lorem ipsum" text in smaller
+// chunks.
+```
+
 ### Customizing `util.inspect` colors
 
 <!-- type=misc -->

lib/util.js

@@ -68,7 +68,8 @@ const inspectDefaultOptions = Object.seal({
   customInspect: true,
   showProxy: false,
   maxArrayLength: 100,
-  breakLength: 60
+  breakLength: 60,
+  compact: true
 });
 
 const propertyIsEnumerable = Object.prototype.propertyIsEnumerable;
@@ -86,6 +87,10 @@ const strEscapeSequencesReplacer = /[\x00-\x1f\x27\x5c]/g;
 const keyStrRegExp = /^[a-zA-Z_][a-zA-Z_0-9]*$/;
 const numberRegExp = /^(0|[1-9][0-9]*)$/;
 
+const readableRegExps = {};
+
+const MIN_LINE_LENGTH = 16;
+
 // Escaped special characters. Use empty strings to fill up unused entries.
 const meta = [
   '\\u0000', '\\u0001', '\\u0002', '\\u0003', '\\u0004',
@@ -276,7 +281,8 @@ function inspect(value, opts) {
     showProxy: inspectDefaultOptions.showProxy,
     maxArrayLength: inspectDefaultOptions.maxArrayLength,
     breakLength: inspectDefaultOptions.breakLength,
-    indentationLvl: 0
+    indentationLvl: 0,
+    compact: inspectDefaultOptions.compact
   };
   // Legacy...
   if (arguments.length > 2) {
@@ -374,7 +380,7 @@ function ensureDebugIsInitialized() {
 function formatValue(ctx, value, recurseTimes, ln) {
   // Primitive types cannot have properties
   if (typeof value !== 'object' && typeof value !== 'function') {
-    return formatPrimitive(ctx.stylize, value);
+    return formatPrimitive(ctx.stylize, value, ctx);
   }
   if (value === null) {
     return ctx.stylize('null', 'null');
@@ -481,10 +487,10 @@ function formatValue(ctx, value, recurseTimes, ln) {
       } catch (e) { /* ignore */ }
 
       if (typeof raw === 'string') {
-        const formatted = formatPrimitive(stylizeNoColor, raw);
+        const formatted = formatPrimitive(stylizeNoColor, raw, ctx);
         if (keyLength === raw.length)
           return ctx.stylize(`[String: ${formatted}]`, 'string');
-        base = ` [String: ${formatted}]`;
+        base = `[String: ${formatted}]`;
         // For boxed Strings, we have to remove the 0-n indexed entries,
         // since they just noisy up the output and are redundant
         // Make boxed primitive Strings look like such
@@ -505,25 +511,25 @@ function formatValue(ctx, value, recurseTimes, ln) {
       const name = `${constructor.name}${value.name ? `: ${value.name}` : ''}`;
       if (keyLength === 0)
         return ctx.stylize(`[${name}]`, 'special');
-      base = ` [${name}]`;
+      base = `[${name}]`;
     } else if (isRegExp(value)) {
       // Make RegExps say that they are RegExps
       if (keyLength === 0 || recurseTimes < 0)
         return ctx.stylize(regExpToString.call(value), 'regexp');
-      base = ` ${regExpToString.call(value)}`;
+      base = `${regExpToString.call(value)}`;
     } else if (isDate(value)) {
       if (keyLength === 0) {
         if (Number.isNaN(value.getTime()))
           return ctx.stylize(value.toString(), 'date');
         return ctx.stylize(dateToISOString.call(value), 'date');
       }
       // Make dates with properties first say the date
-      base = ` ${dateToISOString.call(value)}`;
+      base = `${dateToISOString.call(value)}`;
     } else if (isError(value)) {
       // Make error with message first say the error
       if (keyLength === 0)
         return formatError(value);
-      base = ` ${formatError(value)}`;
+      base = `${formatError(value)}`;
     } else if (isAnyArrayBuffer(value)) {
       // Fast path for ArrayBuffer and SharedArrayBuffer.
       // Can't do the same for DataView because it has a non-primitive
@@ -553,13 +559,13 @@ function formatValue(ctx, value, recurseTimes, ln) {
         const formatted = formatPrimitive(stylizeNoColor, raw);
         if (keyLength === 0)
           return ctx.stylize(`[Number: ${formatted}]`, 'number');
-        base = ` [Number: ${formatted}]`;
+        base = `[Number: ${formatted}]`;
       } else if (typeof raw === 'boolean') {
         // Make boxed primitive Booleans look like such
         const formatted = formatPrimitive(stylizeNoColor, raw);
         if (keyLength === 0)
           return ctx.stylize(`[Boolean: ${formatted}]`, 'boolean');
-        base = ` [Boolean: ${formatted}]`;
+        base = `[Boolean: ${formatted}]`;
       } else if (typeof raw === 'symbol') {
         const formatted = formatPrimitive(stylizeNoColor, raw);
         return ctx.stylize(`[Symbol: ${formatted}]`, 'symbol');
@@ -603,9 +609,42 @@ function formatNumber(fn, value) {
   return fn(`${value}`, 'number');
 }
 
-function formatPrimitive(fn, value) {
-  if (typeof value === 'string')
+function formatPrimitive(fn, value, ctx) {
+  if (typeof value === 'string') {
+    if (ctx.compact === false &&
+      value.length > MIN_LINE_LENGTH &&
+      ctx.indentationLvl + value.length > ctx.breakLength) {
+      // eslint-disable-next-line max-len
+      const minLineLength = Math.max(ctx.breakLength - ctx.indentationLvl, MIN_LINE_LENGTH);
+      // eslint-disable-next-line max-len
+      const averageLineLength = Math.ceil(value.length / Math.ceil(value.length / minLineLength));
+      const divisor = Math.max(averageLineLength, MIN_LINE_LENGTH);
+      var res = '';
+      if (readableRegExps[divisor] === undefined) {
+        // Build a new RegExp that naturally breaks text into multiple lines.
+        //
+        // Rules
+        // 1. Greedy match all text up the max line length that ends with a
+        //    whitespace or the end of the string.
+        // 2. If none matches, non-greedy match any text up to a whitespace or
+        //    the end of the string.
+        //
+        // eslint-disable-next-line max-len, no-unescaped-regexp-dot
+        readableRegExps[divisor] = new RegExp(`(.|\\n){1,${divisor}}(\\s|$)|(\\n|.)+?(\\s|$)`, 'gm');
+      }
+      const indent = ' '.repeat(ctx.indentationLvl);
+      const matches = value.match(readableRegExps[divisor]);
+      if (matches.length > 1) {
+        res += `${fn(strEscape(matches[0]), 'string')} +\n`;
+        for (var i = 1; i < matches.length - 1; i++) {
+          res += `${indent}  ${fn(strEscape(matches[i]), 'string')} +\n`;
+        }
+        res += `${indent}  ${fn(strEscape(matches[i]), 'string')}`;
+        return res;
+      }
+    }
     return fn(strEscape(value), 'string');
+  }
   if (typeof value === 'number')
     return formatNumber(fn, value);
   if (typeof value === 'boolean')
@@ -806,7 +845,7 @@ function formatProperty(ctx, value, recurseTimes, key, array) {
   const desc = Object.getOwnPropertyDescriptor(value, key) ||
     { value: value[key], enumerable: true };
   if (desc.value !== undefined) {
-    const diff = array === 0 ? 3 : 2;
+    const diff = array !== 0 || ctx.compact === false ? 2 : 3;
     ctx.indentationLvl += diff;
     str = formatValue(ctx, desc.value, recurseTimes, array === 0);
     ctx.indentationLvl -= diff;
@@ -839,25 +878,36 @@ function formatProperty(ctx, value, recurseTimes, key, array) {
 
 function reduceToSingleString(ctx, output, base, braces, addLn) {
   const breakLength = ctx.breakLength;
+  var i = 0;
+  if (ctx.compact === false) {
+    const indentation = ' '.repeat(ctx.indentationLvl);
+    var res = `${base ? `${base} ` : ''}${braces[0]}\n${indentation}  `;
+    for (; i < output.length - 1; i++) {
+      res += `${output[i]},\n${indentation}  `;
+    }
+    res += `${output[i]}\n${indentation}${braces[1]}`;
+    return res;
+  }
   if (output.length * 2 <= breakLength) {
     var length = 0;
-    for (var i = 0; i < output.length && length <= breakLength; i++) {
+    for (; i < output.length && length <= breakLength; i++) {
       if (ctx.colors) {
         length += removeColors(output[i]).length + 1;
       } else {
         length += output[i].length + 1;
       }
     }
     if (length <= breakLength)
-      return `${braces[0]}${base} ${join(output, ', ')} ${braces[1]}`;
+      return `${braces[0]}${base ? ` ${base}` : ''} ${join(output, ', ')} ` +
+        braces[1];
   }
   // If the opening "brace" is too large, like in the case of "Set {",
   // we need to force the first item to be on the next line or the
   // items will not line up correctly.
   const indentation = ' '.repeat(ctx.indentationLvl);
   const extraLn = addLn === true ? `\n${indentation}` : '';
   const ln = base === '' && braces[0].length === 1 ?
-    ' ' : `${base}\n${indentation}  `;
+    ' ' : `${base ? ` ${base}` : base}\n${indentation}  `;
   const str = join(output, `,\n${indentation}  `);
   return `${extraLn}${braces[0]}${ln}${str} ${braces[1]}`;
 }