jest-diff: Replace diff with diff-sequences package #6961

pedrottimark · 2018-09-11T19:43:00Z

Summary

Fixes #1772 #5392 besser spät als nie :)

Much faster when number of changed lines is large: less memory and fewer iterations.

The baseline and improved versions report the same number of changed versus common lines.

This a breaking change from viewpoint of dependents like snapshot-diff or snapshot-diff-serializer package which use output of jest-diff as a test criterion instead of a report.

/cc @thymikee @wldcordeiro

Given received and expected values, the improved version can return different particular lines as inserted, deleted, or common than the baseline version (especially for swapped lines, see below).

In case you ask why different particular lines, because diff-sequences can often return 2 differences per bisection to minimize depth of recursive calls, it might find alternative path in edit graph.

The tests for snapshot-diff still pass.

For realistic differences of .js, .json, .md, and .snap files, only 12.2% = 1259 / 10306 had exactly the same ~~changed~~ output in offline comparison of baseline to improved versions of jest-diff in the 2000 commits going back in history from Jest 23.5.0.

For --expand option, the improved code is based on documentation:
https://github.com/facebook/jest/tree/master/packages/diff-sequences#example-of-callback-functions-to-format-diff-lines
For default --no-expand option, the foundSubsequences callback function emulates the hunk and patch logic from diff package: application-specific logic moves into jest-diff package.

By the way, Jest still has diff as a dependence:

yarn why diff
   - "_project_#mocha" depends on it
   - Hoisted from "_project_#mocha#diff"
   - Hoisted from "_project_#example-typescript#ts-jest#jest-config#jest-jasmine2#jest-diff#diff"

Test plan

Updated 6 snapshots for collapses big diffs to patch format and context tests:

Expected: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
Received: [1, 2, 3, 4, 5, 6, 7, 8, 10, 9]

Differences in baseline version, that is, 10 is change, 9 is common:

+ 10
  9
- 10

Differences in improved version, that is, 9 is change, 10 is common:

- 9
  10
+ 9

Updated 4 snapshots in matchers.test.js of expect package:

Expected: [2, 1] or {2: "two", 1: "one"}
Received: [1, 2] or {1: "one", 2: "two"}

Differences in baseline version, that is, 1 is change, 2 is common:

+ 1
  2
- 1

Differences in improved version, that is, 2 is change, 1 is common:

- 2
  1
+ 2

codecov-io · 2018-09-11T20:05:10Z

Codecov Report

Merging #6961 into master will increase coverage by 0.13%.
The diff coverage is 98.48%.

@@            Coverage Diff            @@
##           master   #6961      +/-   ##
=========================================
+ Coverage   66.86%     67%   +0.13%     
=========================================
  Files         250     250              
  Lines       10460   10510      +50     
  Branches        3       3              
=========================================
+ Hits         6994    7042      +48     
- Misses       3465    3467       +2     
  Partials        1       1

Impacted Files	Coverage Δ
packages/jest-diff/src/diff_strings.js	`98.52% <98.48%> (-1.48%)`	⬇️

Continue to review full report at Codecov.

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SimenB · 2018-09-11T21:09:46Z

Wooooooo! I've been waiting for this! 😀

This a breaking change from viewpoint of dependents like snapshot-diff or snapshot-diff-serializer package which use output of jest-diff as a test criterion instead of a report.

React also uses jest-diff, mind seeing if this breaks them as well? We're gearing up for a major now anyways (due to the Babel 7 change), so the fact it's breaking is in and of itself not an issue 🙂

SimenB · 2018-09-11T21:10:14Z

CHANGELOG.md

@@ -1,5 +1,9 @@
 ## master

+### Features
+
+- `[jest-diff]` Replace `diff` with `diff-sequences` package ([#6961](https://github.com/facebook/jest/pull/6961))


Add **Breaking** as well if it is? 🙂

SimenB · 2018-09-11T21:11:22Z

Also, is this a pure performance change or is the visual output for users different? If the latter, mind adding some screenshots?

EDIT: nvm, I just red your OP more thoroughly, and you've included some example, which both makes perfect sense 🙂

pedrottimark · 2018-09-11T21:27:28Z

Goal for this pull request is improve performance. A separate pull request #6917 explains in ExpectAPI.md how to rewrite assertions that now will run faster, but still output large irrelevant diffs.

The formatting remains the same, so most dependents which use jest-diff to report test failures, won’t notice the difference, pardon the pun.

pedrottimark · 2018-09-11T21:52:04Z

To answer your question about React, here is what I did:

clone repository
yarn
yarn link jest-diff
yarn test passed
yarn test-prod passed

wldcordeiro · 2018-09-12T05:41:24Z

Thanks for the heads up! I'll take this into account when I bump the dependencies.

thymikee

I just had a quick glance, so I left some nits. Can you share any perf numbers for smaller and larger diffs? Does it affect overall perf of our suite for example?

thymikee · 2018-09-20T08:07:26Z

packages/jest-diff/src/diff_strings.js

+  aStart: number,
+  aEnd: number,
+  aLinesUn: Array<string>,
+  aLinesIn: Array<string>,


Can we change the variables names?
aStart -> start
aLinesUn -> linesUnchanged
etc

This comment is valid for all names like these (except when it makes sense where you have a,b related args)

I will review naming and think how to improve comments here to make it less surprising.

The reason for a prefix in formatDelete and b prefix in formatInsert is to remind me assumption or convention that took me a while to understand:

differences in expected value are always formatted as deleted

differences in received value are always formatted as inserted

thymikee · 2018-09-20T08:09:48Z

packages/jest-diff/src/diff_strings.js

+const fgDelete = chalk.green;
+const fgInsert = chalk.red;
+const fgUnchanged = chalk.dim; // common lines (even indentation same)
+const fgInchanged = chalk.cyan; // common lines (only indentation different)


fgIndent maybe? Inchanged sounds weird

replace with

fgUnchanged fgCommon

fgInchanged fgIndent

bgUnchanged bgCommon

bgDefault bgInverse

I like those suggestions!

SimenB · 2018-09-20T08:42:15Z

Can you share any perf numbers for smaller and larger diffs?

Might be a good idea to create a performance suite for this, similar to https://github.com/facebook/jest/tree/master/packages/pretty-format/perf

(although I would prefer it to be written in https://github.com/bestiejs/benchmark.js/ or something and not something home cooked)

pedrottimark · 2018-09-20T19:13:02Z

@thymikee A performance suite in diff-sequences package is super suggestion.

The problem solved by replacing diff package is when Jest reports test failure and serialization of received value has huge number of inserted lines:

Jest stalls after comparing to complex objects #1772 incorrect received value before behavior has been implemented in TDD process
Jest tests hanging forever with large snapshot changes #5392 unexpected received value because of mistake in writing an assertion

@SimenB Thank you for suggesting benchmark.js package for a performance suite.

I will convert perf test for pretty-format as warm up exercise. Your comment about “home cooked” is on target. I had to adapt it (offline) quite a bit to get useful feedback that correctness improvements did not cause performance regressions.

SimenB · 2018-09-20T19:25:51Z

Got a PR using benchtable in another project I'm maintaining, you can look into that as an alternative to plain benchmark.js (it has a slightly easier API, and a prettier reporter)

SimenB · 2018-09-24T09:07:28Z

Btw, #4619 is back on the table after this is merged, right?

SimenB · 2018-09-24T09:09:23Z

CHANGELOG.md

@@ -1,5 +1,9 @@
 ## master

+### Features
+
+- Breaking Change: `[jest-diff]` Replace `diff` with `diff-sequences` package ([#6961](https://github.com/facebook/jest/pull/6961))


We use the format:

- `[jest-diff]` [**BREAKING**] blablabla

hisapy · 2018-10-12T04:24:59Z

I'm having this problem #1772 (comment) ... do you think I can solve it after this PR is merged? .. or do you think I can install jest from the fork so I can experiment with it ?

thymikee · 2018-10-12T06:43:58Z

Feel free to play with it :)

SimenB · 2018-10-12T07:14:09Z

@pedrottimark any news on that benchmark? :) I think we're good to land as soon as those are in place

Also, semi related: prettier/prettier#4816

hisapy · 2018-10-12T16:01:58Z

I played with this PR in my project and apparently it feels faster than 23.6.0, having snapshots > 1MB

stephanschubert · 2018-10-13T20:18:22Z

@hisapy Why not time jest ... it?

hisapy · 2018-10-14T15:20:30Z

@hisapy Why not time jest ... it?

That's a good idea. Too bad I didn't think of it before trying this fork. I was in a real hurry and I just wanted to link this to my project and get it working.

Just for the record, I first tried to yarn link from the root dir of jest but I got some errors. The correct procedure is to yarn link from package in the packages dir. And in this sense, at first I just linked jest and the first I noticed was that my test, instead of hanging for long minutes, failed faster, with the same memory heap error .... Luckily I had my debugger ON and I quickly noticed that my test was using the old jest-diff so I also linked the jest-diff package from this branch ... although I had the same error, I believe that it got to it faster.

Finally, after some checks I would've done before chasing the error in jest, I realized that my snapshot tests were failing because I had some snapshots with really huge sizes (35MB, 13MB being the largest) so I came with strategy of splitting the snapshots in multiple files and now the largest are at most ~1.4MB, which run just fine.

I hope I can fix some other stuff quickly so I can time this with fully green snapshots in my test suite.

canemacchina · 2018-10-18T13:41:18Z

@SimenB could this fix be integrated in jest before Jest 24 milestone?
the issue #1772 is quite blocking for me, and if there are no reason to wait for next milestone, I can't understand why this fix can't be released before...

pedrottimark · 2018-10-18T13:43:50Z

I will work on performance benchmark over the week end.

SimenB · 2018-10-18T13:46:29Z

@canemacchina we've already landed breaking changes in master (and this is a breaking change in and of itself), so this won't be released before Jest 24. Sorry!

canemacchina · 2018-10-18T13:50:32Z

Oh... Well, I'll wait!

Thanks anyway!

lochness42 · 2018-11-13T10:47:30Z

This would be really appreciated addition as I'm having hanging tests with storyshots which is using snapshots under the hood.

SimenB · 2018-11-13T23:49:25Z

@rubennorte could you run this diff on fb and see if either functionality or performance regresses?

SimenB · 2018-12-26T11:56:07Z

@rickhanlonii maybe you can?

thymikee · 2019-01-10T10:01:47Z

@pedrottimark mind resolving conflicts?

thymikee · 2019-01-11T21:57:15Z

@rubennorte @rickhanlonii we'd appreciate testing this at FB scale. For now I feel like we're ready to merge it

pedrottimark · 2019-01-11T22:22:59Z

Think of small changes to cause toEqual and toMatchSnapshot tests to fail and display diff.

* jest-diff: Replace diff with diff-sequences package * Update CHANGELOG.md * Add Breaking Change in CHANGELOG.md * Rename 4 variables for chalk colors

github-actions · 2021-05-12T04:08:42Z

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.
Please note this issue tracker is not a help forum. We recommend using StackOverflow or our discord channel for questions.

jest-diff: Replace diff with diff-sequences package

1c901aa

facebook-github-bot added the cla signed label Sep 11, 2018

Update CHANGELOG.md

f9060ea

SimenB requested a review from cpojer September 11, 2018 21:09

SimenB reviewed Sep 11, 2018

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Add Breaking Change in CHANGELOG.md

573e63d

SimenB requested review from rickhanlonii and thymikee September 12, 2018 06:44

pedrottimark mentioned this pull request Sep 13, 2018

If the received is different from the expected in some obvious way, reject it without full diff #6976

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pedrottimark added 2 commits September 24, 2018 13:13

Resolve merge conflict and fix CHANGELOG.md

80f4675

Rename 4 variables for chalk colors

dd30440

SimenB added this to the Jest 24 milestone Oct 16, 2018

SimenB mentioned this pull request Oct 24, 2018

Jest stalls after comparing to complex objects #1772

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Resolve merge conflict in CHANGELOG.md

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SimenB approved these changes Jan 10, 2019

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SimenB mentioned this pull request Jan 10, 2019

Jest diff numbers and booleans #7605

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thymikee approved these changes Jan 11, 2019

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thymikee merged commit 60ca308 into jestjs:master Jan 11, 2019

pedrottimark deleted the replace-diff branch January 11, 2019 22:20

SimenB mentioned this pull request Jan 11, 2019

Jest tests hanging forever with large snapshot changes #5392

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replace	with
`fgUnchanged`	`fgCommon`
`fgInchanged`	`fgIndent`
`bgUnchanged`	`bgCommon`
`bgDefault`	`bgInverse`

jest-diff: Replace diff with diff-sequences package #6961

jest-diff: Replace diff with diff-sequences package #6961

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Summary

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