From 02c44a48943302d07a3b9575402a8992e57dada8 Mon Sep 17 00:00:00 2001
From: Ruben Bridgewater <ruben@bridgewater.de>
Date: Mon, 24 Sep 2018 10:15:52 +0200
Subject: [PATCH] assert: reduce diff noise

Assertion errors that produce a diff show a diff for identical entries
in case one side of the comparison has more object properties than the
other one. Those lines are now taken into account and will not show up
as diverging lines anymore.

Refs: https://github.com/nodejs/node/issues/22763

PR-URL: https://github.com/nodejs/node/pull/23048
Refs: https://github.com/nodejs/node/issues/22763
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Shingo Inoue <leko.noor@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
---
 lib/internal/assert.js            | 55 +++++++++++++++++++------------
 test/parallel/test-assert-deep.js | 24 +++++++++-----
 2 files changed, 50 insertions(+), 29 deletions(-)

diff --git a/lib/internal/assert.js b/lib/internal/assert.js
index 92c2a1d0af893e..d3155cf692eebe 100644
--- a/lib/internal/assert.js
+++ b/lib/internal/assert.js
@@ -205,29 +205,42 @@ function createErrDiff(actual, expected, operator) {
       res += `\n${green}+${white} ${actualLines[i]}`;
       printedLines++;
     // Lines diverge
-    } else if (actualLines[i] !== expectedLines[i]) {
-      if (cur > 1 && i > 2) {
-        if (cur > 4) {
-          res += `\n${blue}...${white}`;
-          skipped = true;
-        } else if (cur > 3) {
-          res += `\n  ${actualLines[i - 2]}`;
+    } else {
+      const expectedLine = expectedLines[i];
+      let actualLine = actualLines[i];
+      let divergingLines = actualLine !== expectedLine &&
+                           (!actualLine.endsWith(',') ||
+                            actualLine.slice(0, -1) !== expectedLine);
+      if (divergingLines &&
+          expectedLine.endsWith(',') &&
+          expectedLine.slice(0, -1) === actualLine) {
+        divergingLines = false;
+        actualLine += ',';
+      }
+      if (divergingLines) {
+        if (cur > 1 && i > 2) {
+          if (cur > 4) {
+            res += `\n${blue}...${white}`;
+            skipped = true;
+          } else if (cur > 3) {
+            res += `\n  ${actualLines[i - 2]}`;
+            printedLines++;
+          }
+          res += `\n  ${actualLines[i - 1]}`;
+          printedLines++;
+        }
+        lastPos = i;
+        res += `\n${green}+${white} ${actualLine}`;
+        other += `\n${red}-${white} ${expectedLine}`;
+        printedLines += 2;
+      // Lines are identical
+      } else {
+        res += other;
+        other = '';
+        if (cur === 1 || i === 0) {
+          res += `\n  ${actualLine}`;
           printedLines++;
         }
-        res += `\n  ${actualLines[i - 1]}`;
-        printedLines++;
-      }
-      lastPos = i;
-      res += `\n${green}+${white} ${actualLines[i]}`;
-      other += `\n${red}-${white} ${expectedLines[i]}`;
-      printedLines += 2;
-    // Lines are identical
-    } else {
-      res += other;
-      other = '';
-      if (cur === 1 || i === 0) {
-        res += `\n  ${actualLines[i]}`;
-        printedLines++;
       }
     }
     // Inspected object to big (Show ~20 rows max)
diff --git a/test/parallel/test-assert-deep.js b/test/parallel/test-assert-deep.js
index 306e8367d45502..3a5fca74d4c287 100644
--- a/test/parallel/test-assert-deep.js
+++ b/test/parallel/test-assert-deep.js
@@ -65,9 +65,13 @@ assert.deepEqual(arr, buf);
     () => assert.deepStrictEqual(buf2, buf),
     {
       code: 'ERR_ASSERTION',
-      message: `${defaultMsgStartFull}\n\n` +
-               '  Buffer [Uint8Array] [\n    120,\n    121,\n    122,\n' +
-               '+   10,\n+   prop: 1\n-   10\n  ]'
+      message: `${defaultMsgStartFull} ... Lines skipped\n\n` +
+               '  Buffer [Uint8Array] [\n' +
+               '    120,\n' +
+               '...\n' +
+               '    10,\n' +
+               '+   prop: 1\n' +
+               '  ]'
     }
   );
   assert.deepEqual(buf2, buf);
@@ -80,9 +84,13 @@ assert.deepEqual(arr, buf);
     () => assert.deepStrictEqual(arr, arr2),
     {
       code: 'ERR_ASSERTION',
-      message: `${defaultMsgStartFull}\n\n` +
-               '  Uint8Array [\n    120,\n    121,\n    122,\n' +
-               '+   10\n-   10,\n-   prop: 5\n  ]'
+      message: `${defaultMsgStartFull} ... Lines skipped\n\n` +
+               '  Uint8Array [\n' +
+               '    120,\n' +
+               '...\n' +
+               '    10,\n' +
+               '-   prop: 5\n' +
+               '  ]'
     }
   );
   assert.deepEqual(arr, arr2);
@@ -822,7 +830,7 @@ assert.throws(
     code: 'ERR_ASSERTION',
     name: 'AssertionError [ERR_ASSERTION]',
     message: `${defaultMsgStartFull}\n\n  ` +
-             '{\n+   a: 4\n-   a: 4,\n-   b: true\n  }'
+             '{\n    a: 4,\n-   b: true\n  }'
   });
 assert.throws(
   () => assert.deepStrictEqual(['a'], { 0: 'a' }),
@@ -891,7 +899,7 @@ assert.deepStrictEqual(obj1, obj2);
   assert.throws(
     () => assert.deepStrictEqual(arrProxy, [1, 2, 3]),
     { message: `${defaultMsgStartFull}\n\n` +
-               '  [\n    1,\n+   2\n-   2,\n-   3\n  ]' }
+               '  [\n    1,\n    2,\n-   3\n  ]' }
   );
   util.inspect.defaultOptions = tmp;