assert: add error diffs

doc/api/assert.md

@@ -17,6 +17,9 @@ For more information about the used equality comparisons see
 <!-- YAML
 added: REPLACEME
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/REPLACEME
+    description: Added error diffs to the strict mode
   - version: REPLACEME
     pr-url: https://github.com/nodejs/node/pull/17002
     description: Added strict mode to the assert module.
@@ -26,12 +29,45 @@ When using the `strict mode`, any `assert` function will use the equality used i
 the strict function mode. So [`assert.deepEqual()`][] will, for example, work the
 same as [`assert.deepStrictEqual()`][].
 
+On top of that, error messages which involve objects produce an error diff
+instead of displaying both objects. That is not the case for the legacy mode.
+
 It can be accessed using:
 
 ```js
 const assert = require('assert').strict;
 ```
 
+Example error diff (the `expected`, `actual`, and `Lines skipped` will be on a
+single row):
+
+```js
+const assert = require('assert').strict;
+
+assert.deepEqual([[[1, 2, 3]], 4, 5], [[[1, 2, '3']], 4, 5]);
+```
+
+```diff
+AssertionError [ERR_ASSERTION]: Input A expected to deepStrictEqual input B:
++ expected
+- actual
+... Lines skipped
+
+  [
+    [
+...
+      2,
+-     3
++     '3'
+    ],
+...
+    5
+  ]
+```
+
+To deactivate the colors, use the `NODE_DISABLE_COLORS` environment variable.
+Please note that this will also deactivate the colors in the REPL.
+
 ## Legacy mode
 
 > Stability: 0 - Deprecated: Use strict mode instead.

doc/api/tty.md

@@ -121,6 +121,32 @@ added: v0.7.7
 A `number` specifying the number of rows the TTY currently has. This property
 is updated whenever the `'resize'` event is emitted.
 
+### writeStream.getColorDepth([env])
+<!-- YAML
+added: REPLACEME
+-->
+
+* `env` {object} A object containing the environment variables to check.
+  Defaults to `process.env`.
+* Returns: {number}
+
+Returns:
+* 1 for 2,
+* 4 for 16,
+* 8 for 256,
+* 24 for 16,777,216
+colors supported.
+
+Use this to determine what colors the terminal supports. Due to the nature of
+colors in terminals it is possible to either have false positives or false
+negatives. It depends on process information and the environment variables that
+may lie about what terminal is used.
+To enforce a specific behavior without relying on `process.env` it is possible
+to pass in an object with different settings.
+
+Use the `NODE_DISABLE_COLORS` environment variable to enforce this function to
+always return 1.
+
 ## tty.isatty(fd)
 <!-- YAML
 added: v0.5.8

lib/assert.js

@@ -48,6 +48,10 @@ const meta = [
 
 const escapeFn = (str) => meta[str.charCodeAt(0)];
 
+const ERR_DIFF_DEACTIVATED = 0;
+const ERR_DIFF_NOT_EQUAL = 1;
+const ERR_DIFF_EQUAL = 2;
+
 // The assert module provides functions that throw
 // AssertionError's when particular conditions are not met. The
 // assert module must conform to the following interface.
@@ -283,7 +287,8 @@ assert.deepStrictEqual = function deepStrictEqual(actual, expected, message) {
       expected,
       message,
       operator: 'deepStrictEqual',
-      stackStartFn: deepStrictEqual
+      stackStartFn: deepStrictEqual,
+      errorDiff: this === strict ? ERR_DIFF_EQUAL : ERR_DIFF_DEACTIVATED
     });
   }
 };
@@ -296,7 +301,8 @@ function notDeepStrictEqual(actual, expected, message) {
       expected,
       message,
       operator: 'notDeepStrictEqual',
-      stackStartFn: notDeepStrictEqual
+      stackStartFn: notDeepStrictEqual,
+      errorDiff: this === strict ? ERR_DIFF_NOT_EQUAL : ERR_DIFF_DEACTIVATED
     });
   }
 }
@@ -308,7 +314,8 @@ assert.strictEqual = function strictEqual(actual, expected, message) {
       expected,
       message,
       operator: 'strictEqual',
-      stackStartFn: strictEqual
+      stackStartFn: strictEqual,
+      errorDiff: this === strict ? ERR_DIFF_EQUAL : ERR_DIFF_DEACTIVATED
     });
   }
 };
@@ -320,7 +327,8 @@ assert.notStrictEqual = function notStrictEqual(actual, expected, message) {
       expected,
       message,
       operator: 'notStrictEqual',
-      stackStartFn: notStrictEqual
+      stackStartFn: notStrictEqual,
+      errorDiff: this === strict ? ERR_DIFF_NOT_EQUAL : ERR_DIFF_DEACTIVATED
     });
   }
 };

lib/internal/errors.js

@@ -14,6 +14,10 @@ const kCode = Symbol('code');
 const kInfo = Symbol('info');
 const messages = new Map();
 
+var green = '';
+var red = '';
+var white = '';
+
 const { errmap } = process.binding('uv');
 const { kMaxLength } = process.binding('buffer');
 const { defineProperty } = Object;
@@ -132,22 +136,171 @@ class SystemError extends makeNodeError(Error) {
   }
 }
 
+function createErrDiff(actual, expected, operator) {
+  var other = '';
+  var res = '';
+  var lastPos = 0;
+  var end = '';
+  var skipped = false;
+  const actualLines = util
+    .inspect(actual, { compact: false }).split('\n');
+  const expectedLines = util
+    .inspect(expected, { compact: false }).split('\n');
+  const msg = `Input A expected to ${operator} input B:\n` +
+        `${green}+ expected${white} ${red}- actual${white}`;
+  const skippedMsg = ' ... Lines skipped';
+
+  // Remove all ending lines that match (this optimizes the output for
+  // readability by reducing the number of total changed lines).
+  var a = actualLines[actualLines.length - 1];
+  var b = expectedLines[expectedLines.length - 1];
+  var i = 0;
+  while (a === b) {
+    if (i++ < 2) {
+      end = `\n  ${a}${end}`;
+    } else {
+      other = a;
+    }
+    actualLines.pop();
+    expectedLines.pop();
+    a = actualLines[actualLines.length - 1];
+    b = expectedLines[expectedLines.length - 1];
+  }
+  if (i > 3) {
+    end = `\n...${end}`;
+    skipped = true;
+  }
+  if (other !== '') {
+    end = `\n  ${other}${end}`;
+    other = '';
+  }
+
+  const maxLines = Math.max(actualLines.length, expectedLines.length);
+  var printedLines = 0;
+  for (i = 0; i < maxLines; i++) {
+    // Only extra expected lines exist
+    const cur = i - lastPos;
+    if (actualLines.length < i + 1) {
+      if (cur > 1 && i > 2) {
+        if (cur > 4) {
+          res += '\n...';
+          skipped = true;
+        } else if (cur > 3) {
+          res += `\n  ${expectedLines[i - 2]}`;
+          printedLines++;
+        }
+        res += `\n  ${expectedLines[i - 1]}`;
+        printedLines++;
+      }
+      lastPos = i;
+      other += `\n${green}+${white} ${expectedLines[i]}`;
+      printedLines++;
+    // Only extra actual lines exist
+    } else if (expectedLines.length < i + 1) {
+      if (cur > 1 && i > 2) {
+        if (cur > 4) {
+          res += '\n...';
+          skipped = true;
+        } else if (cur > 3) {
+          res += `\n  ${actualLines[i - 2]}`;
+          printedLines++;
+        }
+        res += `\n  ${actualLines[i - 1]}`;
+        printedLines++;
+      }
+      lastPos = i;
+      res += `\n${red}-${white} ${actualLines[i]}`;
+      printedLines++;
+    // Lines diverge
+    } else if (actualLines[i] !== expectedLines[i]) {
+      if (cur > 1 && i > 2) {
+        if (cur > 4) {
+          res += '\n...';
+          skipped = true;
+        } else if (cur > 3) {
+          res += `\n  ${actualLines[i - 2]}`;
+          printedLines++;
+        }
+        res += `\n  ${actualLines[i - 1]}`;
+        printedLines++;
+      }
+      lastPos = i;
+      res += `\n${red}-${white} ${actualLines[i]}`;
+      other += `\n${green}+${white} ${expectedLines[i]}`;
+      printedLines += 2;
+    // Lines are identical
+    } else {
+      res += other;
+      other = '';
+      if (cur === 1 || i === 0) {
+        res += `\n  ${actualLines[i]}`;
+        printedLines++;
+      }
+    }
+    // Inspected object to big (Show ~20 rows max)
+    if (printedLines > 20 && i < maxLines - 2) {
+      return `${msg}${skippedMsg}\n${res}\n...${other}\n...`;
+    }
+  }
+  return `${msg}${skipped ? skippedMsg : ''}\n${res}${other}${end}`;
+}
+
 class AssertionError extends Error {
   constructor(options) {
     if (typeof options !== 'object' || options === null) {
       throw new exports.TypeError('ERR_INVALID_ARG_TYPE', 'options', 'Object');
     }
-    var { actual, expected, message, operator, stackStartFn } = options;
+    var {
+      actual,
+      expected,
+      message,
+      operator,
+      stackStartFn,
+      errorDiff = 0
+    } = options;
+
     if (message != null) {
       super(message);
     } else {
+      if (util === null) {
+        util = require('util');
+        if (process.stdout.isTTY && process.stdout.getColorDepth() !== 1) {
+          green = '\u001b[32m';
+          white = '\u001b[39m';
+          red = '\u001b[31m';
+        }
+      }
+
       if (actual && actual.stack && actual instanceof Error)
         actual = `${actual.name}: ${actual.message}`;
       if (expected && expected.stack && expected instanceof Error)
         expected = `${expected.name}: ${expected.message}`;
-      if (util === null) util = require('util');
-      super(`${util.inspect(actual).slice(0, 128)} ` +
-        `${operator} ${util.inspect(expected).slice(0, 128)}`);
+
+      if (errorDiff === 0) {
+        let res = util.inspect(actual);
+        let other = util.inspect(expected);
+        if (res.length > 128)
+          res = `${res.slice(0, 125)}...`;
+        if (other.length > 128)
+          other = `${other.slice(0, 125)}...`;
+        super(`${res} ${operator} ${other}`);
+      } else if (errorDiff === 1) {
+        // In case the objects are equal but the operator requires unequal, show
+        // the first object and say A equals B
+        const res = util
+          .inspect(actual, { compact: false }).split('\n');
+
+        if (res.length > 20) {
+          res[19] = '...';
+          while (res.length > 20) {
+            res.pop();
+          }
+        }
+        // Only print a single object.
+        super(`Identical input passed to ${operator}:\n${res.join('\n')}`);
+      } else {
+        super(createErrDiff(actual, expected, operator));
+      }
     }
 
     this.generatedMessage = !message;

lib/internal/url.js

@@ -6,7 +6,7 @@ const {
   isHexTable
 } = require('internal/querystring');
 
-const { getConstructorOf } = require('internal/util');
+const { getConstructorOf, removeColors } = require('internal/util');
 const errors = require('internal/errors');
 const querystring = require('querystring');
 
@@ -181,9 +181,8 @@ class URLSearchParams {
     for (var i = 0; i < list.length; i += 2)
       output.push(`${innerInspect(list[i])} => ${innerInspect(list[i + 1])}`);
 
-    var colorRe = /\u001b\[\d\d?m/g;
     var length = output.reduce(
-      (prev, cur) => prev + cur.replace(colorRe, '').length + separator.length,
+      (prev, cur) => prev + removeColors(cur).length + separator.length,
       -separator.length
     );
     if (length > ctx.breakLength) {

lib/internal/util.js

@@ -17,6 +17,12 @@ const noCrypto = !process.versions.openssl;
 
 const experimentalWarnings = new Set();
 
+const colorRegExp = /\u001b\[\d\d?m/g;
+
+function removeColors(str) {
+  return str.replace(colorRegExp, '');
+}
+
 function isError(e) {
   return objectToString(e) === '[object Error]' || e instanceof Error;
 }
@@ -347,6 +353,7 @@ module.exports = {
   objectToString,
   promisify,
   spliceOne,
+  removeColors,
 
   // Symbol used to customize promisify conversion
   customPromisifyArgs: kCustomPromisifyArgsSymbol,