Large diffs do not show

[silverwind]

Describe the bug

vitest does not render large object diffs. The config options outputDiffLines: Infinity, and outputTruncateLength: Infinity seem to have no effect, it shows this unhelpful message with no diff visible at all:

AssertionError: expected [ Array(500) ] to deeply equal [ Array(500) ]

Reproduction

https://github.com/silverwind/vitest-diff

Clone, npm install and npx vitest yields this unhelpful output:

 RUN  v0.25.8 /Users/silverwind/git/vitest-diff

 ❯ test.js (1)
   × diff

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ Failed Tests 1 ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯

 FAIL  test.js > diff
AssertionError: expected [ Array(500) ] to deeply equal [ Array(500) ]
 ❯ test.js:6:13
      4|   const a = JSON.parse(readFileSync(new URL("a.json", import.meta.url), "utf8"));
      5|   const b = JSON.parse(readFileSync(new URL("b.json", import.meta.url), "utf8"));
      6|   expect(a).toEqual(b);
       |             ^
      7| });
      8|



⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯[1/1]⎯

 Test Files  1 failed (1)
      Tests  1 failed (1)
   Start at  13:09:01
   Duration  1.28s (transform 339ms, setup 0ms, collect 3ms, tests 56ms)

System Info

System:
    OS: macOS 13.0.1
    CPU: (8) x64 Intel(R) Core(TM) i7-1060NG7 CPU @ 1.20GHz
    Memory: 153.65 MB / 16.00 GB
    Shell: 5.9 - /usr/local/bin/zsh
  Binaries:
    Node: 19.2.0 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 8.19.3 - /usr/local/bin/npm
  npmPackages:
    vitest: 0.25.8 => 0.25.8

Used Package Manager

npm

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[silverwind]

Thanks for the new options. I updated the repro and it does at least now render part of the diff, although it is pretty slow, took around 20 seconds to produce the output on my machine.

Still, it's only rendering part of the diff, and it's hiding 4951 lines, is it expected?

  - Expected  - 1500
  + Received  + 1500

      Object {
        "address": Object {
  -       "city": "Sandoná",
  -       "street": "35539 Nolan Lights",
  +       "city": "Vatican City",
  +       "street": "95452 Davion Grove",
        },
  -     "full name": "Hilda Labadie",
  +     "full name": "Corey Maggio",
      },
      Object {
        "address": Object {
  -       "city": "Benkovac",
  -       "street": "1515 Dietrich Lights",
  +       "city": "Thaton",
  +       "street": "8704 Trey Motorway",
        },
  -     "full name": "Stacy Lakin",
  +     "full name": "Kelvin Jaskolski",
      },
      Object {
        "address": Object {
  -       "city": "Pizitou",
  -       "street": "84570 Jay Fall",
  +       "city": "Iriba",
  +       "street": "89217 Hyatt Dale",
        },
  -     "full name": "Lana Klocko",
  +     "full name": "Connie Considine",
      },
      Object {
        "address": Object {
  -       "city": "Grenville",
  -       "street": "73389 Stamm Land",
  +       "city": "As Samawah",
  +       "street": "2630 Sincere Avenue",
        },
  -     "full name": "Louis Jones",
  +     "full name": "Tabitha Nikolaus",
      },
      Object {
        "address": Object {
  -       "city": "Quruqsoy",
  -       "street": "674 Kreiger Avenue",
  +       "city": "La Fermina",
  +       "street": "760 Gillian Prairie",
        },
  -     "full name": "Gerard Mills",
  +     "full name": "Claire D'Amore",
  ... 4951 more lines

[sheremet-va]

Yes, look into the new options to display more.

[sheremet-va]

We are comparing objects as strings, and it is very slow, yes. This is why it’s nor enabled by default.

[silverwind]

The new options are already all set to Infinity, so that seems to not be enough to show all lines.

Regarding text diff performance, I had good experience with jsdiff diffLines, maybe worth looking into.

[sheremet-va]

The new options are already all set to Infinity, so that seems to not be enough to show all lines.

I forgot to pass them down 🤦🏻 --outputDiffMaxLines is the one you need here.

[sheremet-va]

#2828 removes these options - please, let me know if it works for you

[silverwind]

Does it mean that diffs will not be cut down by any arbitrary limits any more and will always show in full? If so I'm happy to accept that, as it reduces my config.

Imho, the default should be unopinionated and just show everything. If users have specific cases where diff gets too large, they can limit it themselves if the new diff package support such a mechanism, but I see that as a completely optional effort on vitest's side to support it.