assert: print more lines in the error diff

So far consequitive identical lines were collapsed if there were at
least three. Now they are only collapsed from five identical lines on.

This also simplifies the implementation a tiny bit by abstracting some
logic.

PR-URL: https://github.com/nodejs/node/pull/28058
Reviewed-By: Rich Trott <rtrott@gmail.com>

lib/internal/assert/assertion_error.js

@@ -122,7 +122,7 @@ function createErrDiff(actual, expected, operator) {
   let a = actualLines[actualLines.length - 1];
   let b = expectedLines[expectedLines.length - 1];
   while (a === b) {
-    if (i++ < 2) {
+    if (i++ < 3) {
       end = `\n  ${a}${end}`;
     } else {
       other = a;
@@ -154,7 +154,9 @@ function createErrDiff(actual, expected, operator) {
     return `${kReadableOperator.notIdentical}\n\n${actualLines.join('\n')}\n`;
   }
 
-  if (i > 3) {
+  // There were at least five identical lines at the end. Mark a couple of
+  // skipped.
+  if (i >= 5) {
     end = `\n${blue}...${white}${end}`;
     skipped = true;
   }
@@ -169,46 +171,46 @@ function createErrDiff(actual, expected, operator) {
         `\n${green}+ actual${white} ${red}- expected${white}`;
   const skippedMsg = ` ${blue}...${white} Lines skipped`;
 
+  let lines = actualLines;
+  let plusMinus = `${green}+${white}`;
+  let maxLength = expectedLines.length;
+  if (actualLines.length < maxLines) {
+    lines = expectedLines;
+    plusMinus = `${red}-${white}`;
+    maxLength = actualLines.length;
+  }
+
   for (i = 0; i < maxLines; i++) {
-    if (actualLines.length < i + 1) {
+    if (maxLength < i + 1) {
-      // If more than one former line is identical, print that. Collapse those
+      // If more than two former lines are identical, print them. Collapse them
-      // in case more than three lines before were identical.
+      // in case more than five lines were identical.
-      if (identical > 1) {
+      if (identical > 2) {
         if (identical > 3) {
+          if (identical > 4) {
+            if (identical === 5) {
+              res += `\n  ${lines[i - 3]}`;
+              printedLines++;
+            } else {
               res += `\n${blue}...${white}`;
               skipped = true;
-        } else if (identical > 2) {
+            }
-          res += `\n  ${expectedLines[i - 2]}`;
+          }
+          res += `\n  ${lines[i - 2]}`;
           printedLines++;
         }
-        res += `\n  ${expectedLines[i - 1]}`;
+        res += `\n  ${lines[i - 1]}`;
         printedLines++;
       }
       // No identical lines before.
       identical = 0;
       // Add the expected line to the cache.
-      other += `\n${red}-${white} ${expectedLines[i]}`;
+      if (lines === actualLines) {
+        res += `\n${plusMinus} ${lines[i]}`;
+      } else {
+        other += `\n${plusMinus} ${lines[i]}`;
+      }
       printedLines++;
     // Only extra actual lines exist
-    } else if (expectedLines.length < i + 1) {
-      // If more than one former line is identical, print that. Collapse those
-      // in case more than three lines before were identical.
-      if (identical > 1) {
-        if (identical > 3) {
-          res += `\n${blue}...${white}`;
-          skipped = true;
-        } else if (identical > 2) {
-          res += `\n  ${actualLines[i - 2]}`;
-          printedLines++;
-        }
-        res += `\n  ${actualLines[i - 1]}`;
-        printedLines++;
-      }
-      // No identical lines before.
-      identical = 0;
-      // Add the actual line to the result.
-      res += `\n${green}+${white} ${actualLines[i]}`;
-      printedLines++;
     // Lines diverge
     } else {
       const expectedLine = expectedLines[i];
@@ -235,13 +237,19 @@ function createErrDiff(actual, expected, operator) {
         actualLine += ',';
       }
       if (divergingLines) {
-        // If more than one former line is identical, print that. Collapse those
+        // If more than two former lines are identical, print them. Collapse
-        // in case more than three lines before were identical.
+        // them in case more than five lines were identical.
-        if (identical > 1) {
+        if (identical > 2) {
           if (identical > 3) {
+            if (identical > 4) {
+              if (identical === 5) {
+                res += `\n  ${actualLines[i - 3]}`;
+                printedLines++;
+              } else {
                 res += `\n${blue}...${white}`;
                 skipped = true;
-          } else if (identical > 2) {
+              }
+            }
             res += `\n  ${actualLines[i - 2]}`;
             printedLines++;
           }
@@ -264,7 +272,7 @@ function createErrDiff(actual, expected, operator) {
         identical++;
         // The very first identical line since the last diverging line is be
         // added to the result.
-        if (identical === 1) {
+        if (identical <= 2) {
           res += `\n  ${actualLine}`;
           printedLines++;
         }

test/parallel/test-assert-deep.js

@@ -53,7 +53,7 @@ assert.throws(
     code: 'ERR_ASSERTION',
     message: `${defaultMsgStartFull} ... Lines skipped\n\n` +
              '+ Uint8Array [\n' +
-             '- Buffer [Uint8Array] [\n    120,\n...\n    10\n  ]'
+             '- Buffer [Uint8Array] [\n    120,\n...\n    122,\n    10\n  ]'
   }
 );
 assert.deepEqual(arr, buf);
@@ -66,9 +66,11 @@ assert.deepEqual(arr, buf);
     () => assert.deepStrictEqual(buf2, buf),
     {
       code: 'ERR_ASSERTION',
-      message: `${defaultMsgStartFull} ... Lines skipped\n\n` +
+      message: `${defaultMsgStartFull}\n\n` +
                '  Buffer [Uint8Array] [\n' +
-               '...\n' +
+               '    120,\n' +
+               '    121,\n' +
+               '    122,\n' +
                '    10,\n' +
                '+   prop: 1\n' +
                '  ]'
@@ -84,9 +86,11 @@ assert.deepEqual(arr, buf);
     () => assert.deepStrictEqual(arr, arr2),
     {
       code: 'ERR_ASSERTION',
-      message: `${defaultMsgStartFull} ... Lines skipped\n\n` +
+      message: `${defaultMsgStartFull}\n\n` +
                '  Uint8Array [\n' +
-               '...\n' +
+               '    120,\n' +
+               '    121,\n' +
+               '    122,\n' +
                '    10,\n' +
                '-   prop: 5\n' +
                '  ]'
@@ -935,7 +939,9 @@ assert.deepStrictEqual(obj1, obj2);
         '+ actual - expected ... Lines skipped\n' +
         '\n' +
         '  Comparison {\n' +
+        "    message: 'Expected values to be strictly deep-equal:\\n' +\n" +
         '...\n' +
+        "      '  [TypeError: foo] {\\n' +\n" +
         "      \"+   foo: 'bar'\\n\" +\n" +
         "+     \"-   foo: 'baz.'\\n\" +\n" +
         "-     \"-   foo: 'baz'\\n\" +\n" +

test/parallel/test-assert.js

@@ -482,12 +482,14 @@ assert.throws(
     '',
     '  [',
     '    [',
-    '...',
+    '      [',
+    '        1,',
     '        2,',
     '+       3',
     "-       '3'",
     '      ]',
     '...',
+    '    4,',
     '    5',
     '  ]'].join('\n');
   assert.throws(
@@ -501,10 +503,12 @@ assert.throws(
     '  [',
     '    1,',
     '...',
+    '    1,',
     '    0,',
     '-   1,',
     '    1,',
     '...',
+    '    1,',
     '    1',
     '  ]'
   ].join('\n');
@@ -521,10 +525,11 @@ assert.throws(
     '  [',
     '    1,',
     '...',
+    '    1,',
     '    0,',
     '+   1,',
     '    1,',
-    '...',
+    '    1,',
     '    1',
     '  ]'
   ].join('\n');

test/pseudo-tty/test-assert-colors.js

@@ -9,7 +9,7 @@ try {
   // active.
   process.env.TERM = 'FOOBAR';
   delete process.env.NODE_DISABLE_COLORS;
-  assert.deepStrictEqual([1, 2, 2, 2], [2, 2, 2, 2]);
+  assert.deepStrictEqual([1, 2, 2, 2, 2], [2, 2, 2, 2, 2]);
 } catch (err) {
   const expected = 'Expected values to be strictly deep-equal:\n' +
     '\u001b[32m+ actual\u001b[39m \u001b[31m- expected\u001b[39m' +
@@ -19,6 +19,7 @@ try {
     '\u001b[31m-\u001b[39m   2,\n' +
     '    2,\n' +
     '\u001b[34m...\u001b[39m\n' +
+    '    2,\n' +
     '    2\n' +
     '  ]';
   assert.strictEqual(err.message, expected);