fix(@angular/cli): batch Prettier invocations during migration formatting

[mdlufy]

Fixes #33597

Problem

formatFiles (packages/angular/cli/src/utilities/prettier.ts) passes every changed file to Prettier as a single execFile argument list:

await execFileAsync(
  process.execPath,
  [prettierCliPath, '--write', '--no-error-on-unmatched-pattern', '--ignore-unknown', ...files],
  { cwd, shell: false },
);

On large repositories (Nx monorepos, migrations touching thousands of files) the combined command line exceeds the OS limit and the spawn is rejected:

• Windows → spawn ENAMETOOLONG (CreateProcess command line capped at 32,767 chars)
• Linux / macOS → spawn E2BIG (argv+envp over ARG_MAX)

The error is caught and only logged, so ng update prints WARNING: Formatting of files failed with the following error: spawn ENAMETOOLONG and silently skips formatting — on exactly the large repos where the migration formatting step is most useful.

Reproduced on Node 26 / macOS (ARG_MAX 1 MiB): 25,000 changed paths ≈ 2 MB of argv → spawn E2BIG.

Fix

Split the file list into batches whose combined argument length stays under a conservative cross-platform budget (32_000, below the Windows 32,767 limit and far below POSIX ARG_MAX), and invoke Prettier once per batch. A single file longer than the budget still gets its own batch, so no file is ever dropped.

The batching logic is extracted into a small pure helper (batchFilesByArgumentLength) so it can be unit-tested deterministically without spawning a process.

Tests

Added prettier_spec.ts covering: empty input, single batch, splitting when the budget is exceeded, reserving the base-argument length in every batch, never dropping an oversized file, and keeping multi-file batches within budget for a 5,000-file set.

Notes

Related but different (already-fixed) code path: angular/angular#57978 (ng build spawn ENAMETOOLONG from many uncommitted files, in compiler-cli).

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[gemini-code-assist]

Code Review

This pull request introduces a batching mechanism to group files when executing Prettier, preventing command-line length limit issues (such as on Windows) when formatting a large number of files. Unit tests have also been added to verify the batching logic. The review feedback suggests improving the accuracy of the command-line length calculation by accounting for argument quoting when paths contain spaces, including the Node executable path in the base length, and adding a corresponding unit test.

[mdlufy]

Thanks for the review! Addressed all three points:

• Quoting for spaces — per-file length now adds the surrounding quotes the OS applies to paths containing spaces (file.length + (file.includes(' ') ? 3 : 1)).
• process.execPath in the base length — good catch; it's spawned as the first argument and counts toward the limit, so baseLength now includes it (and applies the same quoting rule to it and prettierCliPath).
• Test — added a case covering the extra length reserved for space-containing paths.

Verified the batching against the repro from #33597 (25k paths on macOS ARG_MAX 1 MiB) — runs across multiple spawns with no E2BIG/ENAMETOOLONG.

[mdlufy]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces batching for files formatted via Prettier to prevent exceeding the OS command-line length limit, adding a helper function batchFilesByArgumentLength along with comprehensive unit tests. The feedback highlights an issue where a failure in an early batch would abort the entire formatting process; catching and aggregating errors across all batches is recommended to preserve the original behavior.

[mdlufy]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a batching mechanism to group files by argument length before executing Prettier, preventing command-line length limit issues (such as E2BIG or ENAMETOOLONG) on systems like Windows when formatting a large number of files. It also adds comprehensive unit tests to verify the batching logic under various conditions. There are no review comments to address, and I have no additional feedback to provide.