Add support for Jest Snapshots

[Nixinova]

• Close Add support for jest snapshots #5564

Description

Support Jest Snapshot files.
Basically JavaScript, but has its own tm-scope to support the highlighting inside `backticks`.
Classify these as generated.

Checklist

• I am adding a new language.
  • The extension of the new language is used in hundreds of repositories on GitHub.com.
    • Search results for each extension:
      • .snap -- 680K files
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample: source
    • Sample license: MIT
  • I have included a syntax highlighting grammar: source, preview (slightly broken)
  • I have updated the heuristics to distinguish my language from others using the same extension.

[Alhadis]

LGTM. 👍

[joscha]

@lildude @Alhadis

We just noticed this change in a pull request review on github and I consider it a regression.

Snapshot tests are often used to accompany meaningful changes. They are more of a blueprint than a fixture in the sense that they can be autogenerated easily and thus may change within a pull request by just adding --update-snapshot to a jest run.
Such changes should not be considered correct, just because the file is generated automatically.

Quite the contrary, the changes in the snapshots are the meaningful change of the test fixture and are thus to be reviewed specifically. As such I believe it is incorrect to mark them as autogenerated by default, as linguist-generated is meant to reduce noise and improve meaningfulness when it comes to displaying a change set. Therefore this change is doing the contrary: it reduces meaninfulness of the displayed change set by hiding potentially vital changes in behaviour of business logic by not displaying the resulting changes in the snapshot fixture.
If (and it is questionable if that makes sense, as it more or less suggests that the snapshot content is meaningless and thus the snapshot change or the code producing the snapshot is meaningless) a snapshot should be hidden I believe this decision should be done on a per-project / repo / folder basis, not as a general change to Linguist's behaviour for all projects based on it. This should be easy by adding a .gitattributes file with **/*.snap linguist-generated=true for the projects that want this.

In github's case there is no way for us to opt out of the default behaviour on an org level for example, making this change even more grave.

[joscha]

I just found: #3874 (comment) where it was reverted before? It seems like this PR follows the exact same premise:

and then #4507 (comment)

?

references

• Hide Jest Snapshot Test Files #3572
• Revert "Added Jest snapshot test files as generated src (#3572)" #3579
• [FOR DISCUSSION]: Hide Jest Snapshot Text Files #3584
• Ignore auto-generated Jest snapshots #4507

[Alhadis]

@joscha Urgh. 😞 I'm so sorry about this. My memory—sharp as it is—isn't infallible, and relying on it to catch these types of scenarios isn't a good idea. We really need to add some sort of record to keep track of important reversions like this, as I predict something like this will happen again in future.

In the mean time, I'll revert the change again and also add a regression test to assert that Jest snapshots are not marked generated by default.

[joscha]

Thank you @Alhadis!