[cknitt]

Split out of #9153.

Ast_derive kept a process-global table of derivers, filled at startup by a side effect in Bs_builtin_ppx. It had a single entry (accessors), and an expression_gen field nothing read. dispatch now matches on the deriver name directly, still giving the removed derivers (abstract, jsConverter) their dedicated errors. Ast_derive_projector exposes check_config, structure_gen and signature_gen as plain functions, and no longer depends on Ast_derive.

A future deriver, for example a user-defined one from compile-time evaluation, would be resolved per compilation in dispatch, from what is in scope. A table filled once when the process starts would be the wrong place for that, especially with rewatch compiling many packages in one process.

New super_errors fixtures, deriving_unknown.res and deriving_accessors_config.res, pin the two error paths dispatch handles. A second commit makes both messages say which attribute is wrong and what to write instead, in the style of the removed-deriver errors:

Code	Before	After
@deriving(lenses)	lenses is not supported	@deriving(lenses) is not supported. The only deriver is @deriving(accessors).
@deriving({accessors: true})	such configuration is not supported	@deriving(accessors) takes no configuration.

Most of the ast_derive_projector.ml diff is re-indentation; with -w it is +41/−83 across the PR.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Kbf3gKyiYMf54wPRxFdUWe

[github-actions]

Changelog

💅 Polish

• Clearer errors for an unknown deriver (@deriving(lenses) is not supported. The only deriver is @deriving(accessors).) and for a configuration passed to @deriving(accessors).

🏠 Internal

• Dispatch @deriving by name instead of through a registry that had a single deriver.

Semantic Diff

2 commits · Full page

Dispatch @deriving by name instead of through a registry

_{2874653 · cknitt + Claude · Oct 31, 2026, 10:20 UTC}

Ast_derive kept a process-global table of derivers, filled at startup by a side effect in Bs_builtin_ppx, with a single entry (accessors) and an expression_gen field nothing read. dispatch now matches the name directly, so it stays the one place a future deriver would be resolved. The projector exposes its generators as plain functions. New super_errors fixtures pin the unknown-deriver and configuration errors, which are unchanged.

✨ Name the deriver in @deriving errors and say what is supported

_{e84079e · cknitt + Claude · Nov 01, 2026, 06:43 UTC · new}

Why

Review: "lenses is not supported" and "such configuration is not supported" didn't say which attribute was wrong or what to write instead. The messages now follow the removed-deriver ones.

Diagnostic modified (unknown deriver)

@deriving(lenses)
type t = {name: string}

diagnostic

-lenses is not supported
+@deriving(lenses) is not supported. The only deriver is @deriving(accessors).

Diagnostic modified (configuration for accessors)

@deriving({accessors: true})
type t = {name: string}

diagnostic

-such configuration is not supported
+@deriving(accessors) takes no configuration.

[codecov]

Codecov Report

❌ Patch coverage is 93.54839% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.75%. Comparing base (8e26a9c) to head (e84079e).

Files with missing lines	Patch %	Lines
compiler/frontend/ast_derive_projector.ml	92.85%	4 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #9157   +/-   ##
=======================================
  Coverage   81.74%   81.75%           
=======================================
  Files         460      460           
  Lines       64944    64941    -3     
=======================================
- Hits        53091    53090    -1     
+ Misses      11853    11851    -2     

Files with missing lines	Coverage Δ
compiler/frontend/ast_derive.ml	100.00% <100.00%> (ø)
compiler/frontend/bs_builtin_ppx.ml	90.33% <ø> (-0.04%)	⬇️
compiler/frontend/ast_derive_projector.ml	92.98% <92.85%> (+2.81%)	⬆️

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[cknitt]

@codex review

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-11-01T06:44:55.539371Z	e84079e	Manual request

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[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Already looking forward to the next diff.

Reviewed commit: e84079e3b4

ℹ️ About Codex in GitHub

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