feat(assert): truncate big diffs

[lionel-rowe]

Fixes #6631

Default behavior remains unchanged. By setting the opt-in DIFF_CONTEXT_LENGTH env var (name subject to bikeshedding), you can enable output like this:

Maybe this needs marked UNSTABLE (unstable version of internal/build-message with unstable versions of assert/equals and assert/strict-equals that are identical apart from doc + dependency change edit: probably better to just parameterize stable version and export a customized version from unstable)

[codecov]

Codecov Report

❌ Patch coverage is 81.35593% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.12%. Comparing base (91d1d55) to head (7645e70).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/truncate_build_message.ts	75.28%	21 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6835      +/-   ##
==========================================
- Coverage   94.16%   94.12%   -0.05%     
==========================================
  Files         573      575       +2     
  Lines       42400    42535     +135     
  Branches     6732     6767      +35     
==========================================
+ Hits        39928    40037     +109     
- Misses       2422     2446      +24     
- Partials       50       52       +2     

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[BlackAsLight]

This looks pretty nice.

On a somewhat related topic I thought I made an issue suggesting directing the output to a file a while ago, but I can't seem to find it. The point being to allow one to parse the difference in an easier manner than in the terminal.

[lionel-rowe]

I thought I made an issue suggesting directing the output to a file

@BlackAsLight Is that necessary as part of the API though? Why not just pipe redirect stderr to a file?

$ NO_COLOR=1 deno eval "import { assertEquals } from 'jsr:@std/assert'; assertEquals(1, 2)" 2> errors.txt
$ cat errors.txt
error: Uncaught (in promise) AssertionError: Values are not equal.


    [Diff] Actual / Expected


-   1
+   2

  throw new AssertionError(message);
        ^
    at assertEquals (https://jsr.io/@std/assert/1.0.14/equals.ts:64:9)
    at file:///root/source/repos/$deno$eval.mts:1:49

[BlackAsLight]

I thought I made an issue suggesting directing the output to a file

@BlackAsLight Is that necessary as part of the API though? Why not just pipe stderr to a file?

$ NO_COLOR=1 deno eval "import { assertEquals } from 'jsr:@std/assert'; assertEquals(1, 2)" 2> errors.txt

$ cat errors.txt

error: Uncaught (in promise) AssertionError: Values are not equal.





    [Diff] Actual / Expected





-   1

+   2



  throw new AssertionError(message);

        ^

    at assertEquals (https://jsr.io/@std/assert/1.0.14/equals.ts:64:9)

    at file:///root/source/repos/$deno$eval.mts:1:49

I didn't think of that, but that also seems pretty verbose and having it send its contents to a specific file only when it errors seems pretty convenient to me.