Enforce function arity in type inclusion and coercion - #8559
Open
cristianoc wants to merge 2 commits into
Open
Conversation
cristianoc
force-pushed
the
codex/function-arity-inclusion
branch
2 times, most recently
from
August 18, 2026 07:45
88d1209 to
1e014c4
Compare
Codecov Report❌ Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## master #8559 +/- ##
=======================================
Coverage 75.79% 75.79%
=======================================
Files 476 476
Lines 62680 62702 +22
=======================================
+ Hits 47506 47525 +19
- Misses 15174 15177 +3
🚀 New features to boost your workflow:
|
rescript
@rescript/belt
@rescript/darwin-arm64
@rescript/darwin-x64
@rescript/linux-arm64
@rescript/linux-x64
@rescript/runtime
@rescript/win32-x64
commit: |
|
Developer playground preview: https://rescript-lang.github.io/rescript/dev-playground/?version=pr-8559 |
cristianoc
marked this pull request as ready for review
August 18, 2026 13:01
![chatgpt-codex-connector[bot]](https://avatars.githubusercontent.com/in/1144995?s=60&v=4){kind=small}
There was a problem hiding this comment.
💡 Codex Review
Here are some automated review suggestions for this pull request.
Reviewed commit: 1e014c4432
ℹ️ About Codex in GitHub
Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you
- Open a pull request for review
- Mark a draft as ready
- Comment "@codex review".
If Codex has suggestions, it will comment; otherwise it will react with 👍.
Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".
cknitt
reviewed
Aug 18, 2026
Add the arity guard (already present in unify) to the Tarrow cases of moregen, eqtype, and subtype_rec. Previously a curried implementation (int => int => int) could satisfy an uncurried interface ((int, int) => int) through signature inclusion or :> coercion; calls made through the interface type compile to direct JavaScript calls with the declared arity, so a first-class use of such a value miscompiled (e.g. returning a closure where an int was expected). The value-mismatch report in includemod now prints a dedicated hint when the two sides are functions of different arities, replacing the vestigial empty curry_kind slot. mcomp is deliberately left arity-lenient: it is an incompatibility oracle for pattern and GADT reasoning, where leniency errs toward "possibly compatible". Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Signed-off-by: Cristiano Calcagno <cristianoc@users.noreply.github.com>
Drop the explanatory second sentence from the signature arity mismatch error; the first sentence already states the problem. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Signed-off-by: Cristiano Calcagno <cristianoc@users.noreply.github.com>
cristianoc
force-pushed
the
codex/function-arity-inclusion
branch
from
August 19, 2026 07:53
a2267c0 to
4dd2af4
Compare
Collaborator
Author
|
@cknitt addressed your comments and evaluated what codex comments have merit. I think this stack of 3 PRs is ready to go. |
cknitt
approved these changes
Aug 19, 2026
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Summary
Why
A curried implementation such as
int => int => intcould previously satisfy an uncurried interface such as(int, int) => int, or be coerced to that type. Calls through the declared interface are emitted as plain JavaScript calls with the declared arity, so first-class uses could return a closure where a value was expected.The root cause was that unification checked arrow arity, while the parallel
moregen,eqtype, andsubtype_recpaths did not.Validation
make testnode tests/build_tests/super_errors/input.jsnode tests/build_tests/super_errors_multi/input.jsmake checkformat