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fix: handle pretty formatting of wide arrays and array-like objects #12402

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merged 11 commits into from
Feb 16, 2022

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Summary

Fixes #12364

Jest will attempt to avoid printing very deeply nested objects beyond a certain depth when writing output from matchers, but it doesn't have the same mechanism for very wide objects.

As a result, very large arrays can cause Jest to run out of memory when a matcher fails and jest attempts to pretty-print the array.

This change introduces a maxWidth parameter to the pretty-format package to complement the existing maxWidth parameter so that it can be used by jest-matcher-utils (and potentially others) to limit the impact of printing very wide objects. For now this applies to Arrays, Sets, and Maps, but in the future could also be used by custom plugins, serializers, or other pretty formatting elements.

Test plan

Added tests to validate the behaviour and tested against code that previously resulted in out-of-memory errors that now fails correctly.

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yay, this is awesome!

also please include a changelog entry 🙂

packages/pretty-format/src/collections.ts Outdated Show resolved Hide resolved
packages/pretty-format/src/collections.ts Outdated Show resolved Hide resolved
packages/pretty-format/src/collections.ts Outdated Show resolved Hide resolved
packages/pretty-format/src/index.ts Outdated Show resolved Hide resolved
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prefer to use these operators where possible on the options object

Refactor requested during review
? ''
: createIndent(options?.indent ?? DEFAULT_OPTIONS.indent),
maxDepth: options?.maxDepth ?? DEFAULT_OPTIONS.maxDepth,
maxWidth: options?.maxWidth ?? DEFAULT_OPTIONS.maxWidth,
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Functionally, the maxWidth is the only newly introduced behaviour in this block. The rest of this block diff is related to a refactor to make use of the safe navigation and null coalescing operators so that

options && options.foo ? options.foo : DEFAULT_OPTIONS.foo

can become

options?.foo ?? DEFAULT_OPTIONS.foo

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CHANGELOG.md Outdated Show resolved Hide resolved
@SimenB SimenB changed the title Fix pretty formatting of wide arrays and array-like objects fix: handle pretty formatting of wide arrays and array-like objects Feb 16, 2022
@SimenB SimenB merged commit 6094810 into jestjs:main Feb 16, 2022
@ryanwilsonperkin ryanwilsonperkin deleted the fix-pretty-printing-wide-objects branch February 16, 2022 13:17
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[Bug]: Jest runs out of memory when trying to print wide objects
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