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Sep 5, 2025
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util: hide duplicated stack frames when using util.inspect #59447

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ea10a7b
util: hide duplicated stack frames when using util.inspect
BridgeAR Aug 11, 2025
5b60626
fixup! improve error message and collapse more lines properly
BridgeAR Aug 12, 2025
17a6673
fixup! improve worst case algorithm perf
BridgeAR Aug 13, 2025
d8a9686
fixup
BridgeAR Aug 18, 2025
72ebdcd
fixup! address comments
BridgeAR Aug 30, 2025
44490c5
fixup! address comments
BridgeAR Sep 2, 2025
8364843
fixup!
BridgeAR Sep 2, 2025
290935d
fixup! address comment
BridgeAR Sep 3, 2025
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134 changes: 131 additions & 3 deletions lib/internal/util/inspect.js
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Original file line number Diff line number Diff line change
Expand Up @@ -1305,13 +1305,122 @@ function identicalSequenceRange(a, b) {
len++;
}
if (len > 3) {
return { len, offset: i };
return [len, i];
}
}
}
}

return { len: 0, offset: 0 };
return [0, 0];
}

function getDuplicateErrorFrameRanges(frames) {
// Build a map: frame line -> sorted list of indices where it occurs
const result = [];
const lineToPositions = new SafeMap();

for (let i = 0; i < frames.length; i++) {
const positions = lineToPositions.get(frames[i]);
if (positions === undefined) {
lineToPositions.set(frames[i], [i]);
} else {
positions[positions.length] = i;
}
}

const minimumDuplicateRange = 3;
// Not enough duplicate lines to consider collapsing
if (frames.length - lineToPositions.size <= minimumDuplicateRange) {
return result;
}

for (let i = 0; i < frames.length - minimumDuplicateRange; i++) {
const positions = lineToPositions.get(frames[i]);
// Find the next occurrence of the same line after i, if any
if (positions.length === 1 || positions[positions.length - 1] === i) {
continue;
}

const current = positions.indexOf(i) + 1;
if (current === positions.length) {
continue;
}

// Theoretical maximum range, adjusted while iterating
let range = positions[positions.length - 1] - i;
if (range < minimumDuplicateRange) {
continue;
}
let extraSteps;
if (current + 1 < positions.length) {
// Optimize initial step size by choosing the greatest common divisor (GCD)
// of all candidate distances to the same frame line. This tends to match
// the true repeating block size and minimizes fallback iterations.
let gcdRange = 0;
for (let j = current; j < positions.length; j++) {
let distance = positions[j] - i;
while (distance !== 0) {
const remainder = gcdRange % distance;
if (gcdRange !== 0) {
// Add other possible ranges as fallback
extraSteps ??= new SafeSet();
extraSteps.add(gcdRange);
}
gcdRange = distance;
distance = remainder;
}
if (gcdRange === 1) break;
}
range = gcdRange;
if (extraSteps) {
extraSteps.delete(range);
extraSteps = [...extraSteps];
}
}
let maxRange = range;
let maxDuplicates = 0;

let duplicateRanges = 0;

for (let nextStart = i + range; /* ignored */ ; nextStart += range) {
let equalFrames = 0;
for (let j = 0; j < range; j++) {
if (frames[i + j] !== frames[nextStart + j]) {
break;
}
equalFrames++;
}
// Adjust the range to match different type of ranges.
if (equalFrames !== range) {
if (!extraSteps?.length) {
break;
}
// Memorize former range in case the smaller one would hide less.
if (duplicateRanges !== 0 && maxRange * maxDuplicates < range * duplicateRanges) {
maxRange = range;
maxDuplicates = duplicateRanges;
}
range = extraSteps.pop();
nextStart = i;
duplicateRanges = 0;
continue;
}
duplicateRanges++;
}

if (maxDuplicates !== 0 && maxRange * maxDuplicates >= range * duplicateRanges) {
range = maxRange;
duplicateRanges = maxDuplicates;
}

if (duplicateRanges * range >= 3) {
result.push(i + range, range, duplicateRanges);
// Skip over the collapsed portion to avoid overlapping matches.
i += range * (duplicateRanges + 1) - 1;
}
}

return result;
}

function getStackString(ctx, error) {
Expand Down Expand Up @@ -1345,14 +1454,33 @@ function getStackFrames(ctx, err, stack) {
const causeStackStart = StringPrototypeIndexOf(causeStack, '\n at');
if (causeStackStart !== -1) {
const causeFrames = StringPrototypeSplit(StringPrototypeSlice(causeStack, causeStackStart + 1), '\n');
const { len, offset } = identicalSequenceRange(frames, causeFrames);
const { 0: len, 1: offset } = identicalSequenceRange(frames, causeFrames);
if (len > 0) {
const skipped = len - 2;
const msg = ` ... ${skipped} lines matching cause stack trace ...`;
frames.splice(offset + 1, skipped, ctx.stylize(msg, 'undefined'));
}
}
}

// Remove recursive repetitive stack frames in long stacks
if (frames.length > 10) {
const ranges = getDuplicateErrorFrameRanges(frames);

for (let i = ranges.length - 3; i >= 0; i -= 3) {
const offset = ranges[i];
const length = ranges[i + 1];
const duplicateRanges = ranges[i + 2];

const msg = ` ... collapsed ${length * duplicateRanges} duplicate lines ` +
'matching above ' +
(duplicateRanges > 1 ?
`${length} lines ${duplicateRanges} times...` :
'lines ...');
frames.splice(offset, length * duplicateRanges, ctx.stylize(msg, 'undefined'));
}
}

return frames;
}

Expand Down
169 changes: 169 additions & 0 deletions test/parallel/test-util-inspect.js
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2920,6 +2920,175 @@ assert.strictEqual(
process.cwd = originalCWD;
}

{
// Use a fake stack to verify the expected colored outcome.
const err = new Error('Hide duplicate frames in long stack');
err.stack = [
'Error: Hide duplicate frames in long stack',
' at A.<anonymous> (/foo/node_modules/bar/baz.js:2:7)',
' at A.<anonymous> (/foo/node_modules/bar/baz.js:2:7)',
' at Module._compile (node:internal/modules/cjs/loader:827:30)',
' at Fancy (node:vm:697:32)',
' at tryModuleLoad (node:internal/modules/cjs/foo:629:12)',
' at Function.Module._load (node:internal/modules/cjs/loader:621:3)',
' at Fancy (node:vm:697:32)',
' at tryModuleLoad (node:internal/modules/cjs/foo:629:12)',
' at Function.Module._load (node:internal/modules/cjs/loader:621:3)',
' at Function.Module._load (node:internal/modules/cjs/loader:621:3)',
' at Function.Module._load (node:internal/modules/cjs/loader:621:3)',
' at Function.Module._load (node:internal/modules/cjs/loader:621:3)',
' at Function.Module._load (node:internal/modules/cjs/loader:621:3)',
' at Function.Module._load (node:internal/modules/cjs/loader:621:3)',
' at Function.Module._load (node:internal/modules/cjs/loader:621:3)',
' at Module.require [as weird/name] (node:internal/aaaaa/loader:735:19)',
' at require (node:internal/modules/helpers:14:16)',
' at Array.forEach (<anonymous>)',
' at require (node:internal/modules/helpers:14:16)',
' at Array.forEach (<anonymous>)',
` at foobar/test/parallel/test-util-inspect.js:2760:12`,
` at Object.<anonymous> (foobar/node_modules/m/folder/file.js:2753:10)`,
' at Module.require [as weird/name] (node:internal/aaaaa/loader:735:19)',
' at require (node:internal/modules/helpers:14:16)',
' at Array.forEach (<anonymous>)',
` at foobar/test/parallel/test-util-inspect.js:2760:12`,
` at Object.<anonymous> (foobar/node_modules/m/folder/file.js:2753:10)`,
' at Module.require [as weird/name] (node:internal/aaaaa/loader:735:19)',
' at require (node:internal/modules/helpers:14:16)',
' at Array.forEach (<anonymous>)',
` at foobar/test/parallel/test-util-inspect.js:2760:12`,
` at Object.<anonymous> (foobar/node_modules/m/folder/file.js:2753:10)`,
' at Module.require [as weird/name] (node:internal/aaaaa/loader:735:19)',
' at require (node:internal/modules/helpers:14:16)',
' at Array.forEach (<anonymous>)',
` at foobar/test/parallel/test-util-inspect.js:2760:12`,
` at Object.<anonymous> (foobar/node_modules/m/folder/file.js:2753:10)`,
' at /test/test-util-inspect.js:2239:9',
' at getActual (node:assert:592:5)',
' at /test/test-util-inspect.js:2239:9',
' at getActual (node:assert:592:5)',
' at /test/test-util-inspect.js:2239:9',
' at getActual (node:assert:592:5)',
].join('\n');

assert.strictEqual(
util.inspect(err, { colors: true }),
'Error: Hide duplicate frames in long stack\n' +
' at A.<anonymous> (/foo/node_modules/\x1B[4mbar\x1B[24m/baz.js:2:7)\n' +
' at A.<anonymous> (/foo/node_modules/\x1B[4mbar\x1B[24m/baz.js:2:7)\n' +
'\x1B[90m at Module._compile (node:internal/modules/cjs/loader:827:30)\x1B[39m\n' +
'\x1B[90m at Fancy (node:vm:697:32)\x1B[39m\n' +
' at tryModuleLoad (node:internal/modules/cjs/foo:629:12)\n' +
'\x1B[90m at Function.Module._load (node:internal/modules/cjs/loader:621:3)\x1B[39m\n' +
'\x1B[90m ... collapsed 3 duplicate lines matching above lines ...\x1B[39m\n' +

'\x1B[90m at Function.Module._load (node:internal/modules/cjs/loader:621:3)\x1B[39m\n' +
'\x1B[90m ... collapsed 5 duplicate lines matching above 1 lines 5 times...\x1B[39m\n' +

' at Module.require [as weird/name] (node:internal/aaaaa/loader:735:19)\n' +
'\x1B[90m at require (node:internal/modules/helpers:14:16)\x1B[39m\n' +
' at Array.forEach (<anonymous>)\n' +
'\x1B[90m at require (node:internal/modules/helpers:14:16)\x1B[39m\n' +
' at Array.forEach (<anonymous>)\n' +
' at foobar/test/parallel/test-util-inspect.js:2760:12\n' +
' at Object.<anonymous> (foobar/node_modules/\x1B[4mm\x1B[24m/folder/file.js:2753:10)\n' +
' at Module.require [as weird/name] (node:internal/aaaaa/loader:735:19)\n' +
'\x1B[90m ... collapsed 10 duplicate lines matching above 5 lines 2 times...\x1B[39m\n' +

'\x1B[90m at require (node:internal/modules/helpers:14:16)\x1B[39m\n' +
' at Array.forEach (<anonymous>)\n' +
' at foobar/test/parallel/test-util-inspect.js:2760:12\n' +
' at Object.<anonymous> (foobar/node_modules/\x1B[4mm\x1B[24m/folder/file.js:2753:10)\n' +
' at /test/test-util-inspect.js:2239:9\n' +
'\x1B[90m at getActual (node:assert:592:5)\x1B[39m\n' +
'\x1B[90m ... collapsed 4 duplicate lines matching above 2 lines 2 times...\x1B[39m',
);

// Use a fake stack to verify the expected colored outcome.
const err2 = new Error('Hide duplicate frames in long stack');
err2.stack = [
'Error: Hide duplicate frames in long stack',
' at A.<anonymous> (/foo/node_modules/bar/baz.js:2:7)',
' at A.<anonymous> (/foo/node_modules/bar/baz.js:2:7)',
' at Module._compile (node:internal/modules/cjs/loader:827:30)',

// 3
' at Fancy (node:vm:697:32)',
' at tryModuleLoad (node:internal/modules/cjs/foo:629:12)',
' at Function.Module._load (node:internal/modules/cjs/loader:621:3)',
' at Fancy (node:vm:697:32)',
' at tryModuleLoad (node:internal/modules/cjs/foo:629:12)',
' at Function.Module._load (node:internal/modules/cjs/loader:621:3)',

// 6 * 1
' at Function.Module._load (node:internal/modules/cjs/loader:621:3)',
' at Function.Module._load (node:internal/modules/cjs/loader:621:3)',
' at Function.Module._load (node:internal/modules/cjs/loader:621:3)',
' at Function.Module._load (node:internal/modules/cjs/loader:621:3)',
' at Function.Module._load (node:internal/modules/cjs/loader:621:3)',
' at Function.Module._load (node:internal/modules/cjs/loader:621:3)',
' at Function.Module._load (node:internal/modules/cjs/loader:621:3)',

// 10
' at require (node:internal/modules/helpers:14:16)',
' at Array.forEach (<anonymous>)',
` at foobar/test/parallel/test-util-inspect.js:2760:12`,
` at Object.<anonymous> (foobar/node_modules/m/folder/file.js:2753:10)`,
' at Module.require [as weird/name] (node:internal/aaaaa/loader:735:19)',
' at Module.require [as weird/name] (node:internal/aaaaa/loader:735:19)',
' at require (node:internal/modules/helpers:14:16)',
' at Array.forEach (<anonymous>)',
` at foobar/test/parallel/test-util-inspect.js:2760:12`,
` at Object.<anonymous> (foobar/node_modules/m/folder/file.js:2753:10)`,

' at require (node:internal/modules/helpers:14:16)',
' at Array.forEach (<anonymous>)',
` at foobar/test/parallel/test-util-inspect.js:2760:12`,
` at Object.<anonymous> (foobar/node_modules/m/folder/file.js:2753:10)`,
' at Module.require [as weird/name] (node:internal/aaaaa/loader:735:19)',
' at Module.require [as weird/name] (node:internal/aaaaa/loader:735:19)',
' at require (node:internal/modules/helpers:14:16)',
' at Array.forEach (<anonymous>)',
` at foobar/test/parallel/test-util-inspect.js:2760:12`,
` at Object.<anonymous> (foobar/node_modules/m/folder/file.js:2753:10)`,

// 2 * 2
' at /test/test-util-inspect.js:2239:9',
' at getActual (node:assert:592:5)',
' at /test/test-util-inspect.js:2239:9',
' at getActual (node:assert:592:5)',
' at /test/test-util-inspect.js:2239:9',
' at getActual (node:assert:592:5)',
].join('\n');

assert.strictEqual(
util.inspect(err2, { colors: true }),
'Error: Hide duplicate frames in long stack\n' +
' at A.<anonymous> (/foo/node_modules/\x1B[4mbar\x1B[24m/baz.js:2:7)\n' +
' at A.<anonymous> (/foo/node_modules/\x1B[4mbar\x1B[24m/baz.js:2:7)\n' +
'\x1B[90m at Module._compile (node:internal/modules/cjs/loader:827:30)\x1B[39m\n' +
'\x1B[90m at Fancy (node:vm:697:32)\x1B[39m\n' +
' at tryModuleLoad (node:internal/modules/cjs/foo:629:12)\n' +
'\x1B[90m at Function.Module._load (node:internal/modules/cjs/loader:621:3)\x1B[39m\n' +
'\x1B[90m ... collapsed 3 duplicate lines matching above lines ...\x1B[39m\n' +
'\x1B[90m at Function.Module._load (node:internal/modules/cjs/loader:621:3)\x1B[39m\n' +
'\x1B[90m ... collapsed 6 duplicate lines matching above 1 lines 6 times...\x1B[39m\n' +
'\x1B[90m at require (node:internal/modules/helpers:14:16)\x1B[39m\n' +
' at Array.forEach (<anonymous>)\n' +
' at foobar/test/parallel/test-util-inspect.js:2760:12\n' +
' at Object.<anonymous> (foobar/node_modules/\x1B[4mm\x1B[24m/folder/file.js:2753:10)\n' +
' at Module.require [as weird/name] (node:internal/aaaaa/loader:735:19)\n' +
' at Module.require [as weird/name] (node:internal/aaaaa/loader:735:19)\n' +
'\x1B[90m at require (node:internal/modules/helpers:14:16)\x1B[39m\n' +
' at Array.forEach (<anonymous>)\n' +
' at foobar/test/parallel/test-util-inspect.js:2760:12\n' +
' at Object.<anonymous> (foobar/node_modules/\x1B[4mm\x1B[24m/folder/file.js:2753:10)\n' +
'\x1B[90m ... collapsed 10 duplicate lines matching above lines ...\x1B[39m\n' +
' at /test/test-util-inspect.js:2239:9\n' +
'\x1B[90m at getActual (node:assert:592:5)\x1B[39m\n' +
'\x1B[90m ... collapsed 4 duplicate lines matching above 2 lines 2 times...\x1B[39m',
);
}

{
// Cross platform checks.
const err = new Error('foo');
Expand Down
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