Show a functor's parameters on hover by cknitt · Pull Request #9083 · rescript-lang/rescript

cknitt · 2026-10-27T13:14:22Z

Fixes #9071. Stacked on #9084, which models an applied functor by its result signature.

Hover on a functor now shows its parameters, for example module MakeSet: (O: Ord) => {...}. Analysis models a functor by its result structure; the parameters are recorded on that structure, and only hover displays them.

An applied functor such as module IntSet = MakeSet(IntOrd) is a plain module and shows no parameters; a partial application shows only the remaining ones, and a generative functor shows () =>.

New analysis test: HoverFunctor (named, multi-parameter, inline-signature, applied, partially applied and generative functors).

🤖 Generated with Claude Code

https://claude.ai/code/session_01Kbf3gLMawVgtmiKy3TMBc3

github-actions · 2026-10-27T13:14:50Z

Changelog

🐛 Bug fix

Hover on a functor shows its parameters, such as module MakeSet: (O: Ord) => {...}, instead of only its body.

Semantic Diff

1 commit · Full page

Show a functor's parameters on hover

_{aac2e68 · cknitt + Claude · Oct 27, 2026, 12:54 UTC}

Why

Editor analysis models a functor by the structure of its result, so hover on a functor showed its body as if it were a plain module, and nothing said it takes arguments. The result structure now records the parameters, and hover prints them in front of the body.

Diagnostic modified (hover on a functor)

module type Ord = {
  type t
  let compare: (t, t) => int
}
module MakeSet = (O: Ord) => {
  type t = array<O.t>
  let add = (s: t, x: O.t) => s->Array.concat([x])
}

rescript · tests/analysis_tests/tests/src/HoverFunctor.res

-module MakeSet: {
+module MakeSet: (O: Ord) => {
   type t = array<O.t>
   let add: (t, O.t) => array<O.t>
 }

Review

Why not add a functor case to the analysis module type? Completion, references and path resolution all treat a functor as its result and would each need the new case; only hover displays the parameters, so they are recorded on the result structure.
What does hover show for an applied functor? A plain module: an application is modelled by its signature, so module IntSet = MakeSet(IntOrd) shows no parameters, and a partial application such as Pair(IntOrd) shows only the remaining one.

codecov · 2026-10-27T13:20:15Z

Codecov Report

❌ Patch coverage is 85.71429% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.47%. Comparing base (c989f87) to head (aac2e68).

Files with missing lines	Patch %	Lines
analysis/src/process_cmt.ml	83.33%	4 Missing ⚠️

Additional details and impacted files

@@                       Coverage Diff                       @@
##           fix-9072-applied-functor-types    #9083   +/-   ##
===============================================================
  Coverage                           81.46%   81.47%           
===============================================================
  Files                                 460      460           
  Lines                               64688    64711   +23     
===============================================================
+ Hits                                52700    52721   +21     
- Misses                              11988    11990    +2

Files with missing lines	Coverage Δ
analysis/src/hover.ml	`77.70% <100.00%> (+0.43%)`	⬆️
analysis/src/shared_types.ml	`80.41% <ø> (ø)`
analysis/src/process_cmt.ml	`83.42% <83.33%> (+0.39%)`	⬆️

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pkg-pr-new · 2026-10-27T13:32:35Z

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npm i https://pkg.pr.new/@rescript/linux-x64@9083

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@rescript/win32-x64

npm i https://pkg.pr.new/@rescript/win32-x64@9083

commit: aac2e68

github-actions · 2026-10-27T13:37:14Z

Developer playground preview: https://rescript-lang.github.io/rescript/dev-playground/?version=pr-9083

cknitt · 2026-10-27T14:20:19Z

@codex review

chatgpt-codex-connector · 2026-10-27T14:20:34Z

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-28T08:01:22.502913Z	`aac2e68`	Manual request

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cknitt · 2026-10-27T19:59:02Z

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chatgpt-codex-connector · 2026-10-27T20:00:45Z

Codex Review: Didn't find any major issues. Bravo.

Reviewed commit: 518b1df249

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cristianoc

Reviewed the hover parameter metadata, applied-signature dependency, and named/multiple/inline/applied/partial/generative fixtures. The reported structural-result case is fixed, and no blocking regression was found. Named-result Ident functors remain a pre-existing limitation. CI analysis tests inspected; tests were not rerun locally.

Why: Editor analysis models a functor by the structure of its result, so hover on a functor showed its body as if it were a plain module, and nothing said it takes arguments. The result structure now records the parameters, and hover prints them in front of the body. Diagnostic modified (hover on a functor): Example: module type Ord = { type t let compare: (t, t) => int } module MakeSet = (O: Ord) => { type t = array<O.t> let add = (s: t, x: O.t) => s->Array.concat([x]) } Before (rescript): tests/analysis_tests/tests/src/HoverFunctor.res module MakeSet: { type t = array<O.t> let add: (t, O.t) => array<O.t> } After (rescript): tests/analysis_tests/tests/src/HoverFunctor.res module MakeSet: (O: Ord) => { type t = array<O.t> let add: (t, O.t) => array<O.t> } Review: Why not add a functor case to the analysis module type? Completion, references and path resolution all treat a functor as its result and would each need the new case; only hover displays the parameters, so they are recorded on the result structure. Review: What does hover show for an applied functor? A plain module: an application is modelled by its signature, so `module IntSet = MakeSet(IntOrd)` shows no parameters, and a partial application such as `Pair(IntOrd)` shows only the remaining one. Fixes: #9071 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Kbf3gLMawVgtmiKy3TMBc3 Signed-off-by: Christoph Knittel <ck@cca.io>

cknitt · 2026-10-28T07:59:22Z

@codex review

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chatgpt-codex-connector · 2026-10-28T08:01:20Z

+  | Structure s -> Structure {s with functor_params = param :: s.functor_params}
+  | Constraint (m1, m2) ->
+    Constraint (add_functor_param param m1, add_functor_param param m2)
+  | Ident _ -> m


Preserve functor parameters on identifier results

For a functor with a named result signature, such as module Make = (O: Ord): Set => {...} or an interface declaration module Make: (O: Ord) => Set, the result becomes Ident Set, and this branch discards the parameter. Hover.show_module subsequently resolves that identifier to Set, so hover still describes Make as a plain module without (O: Ord) =>. The same loss occurs for functors whose body returns a module identifier. Preserve the parameters independently of the result's representation and carry them through identifier resolution.

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cknitt marked this pull request as ready for review October 27, 2026 14:20

chatgpt-codex-connector Bot reviewed Oct 27, 2026

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Comment thread analysis/src/hover.ml

cknitt force-pushed the fix-9071-functor-hover branch from 71fcc36 to 518b1df Compare October 27, 2026 19:58

cknitt changed the base branch from master to fix-9072-applied-functor-types October 27, 2026 19:58

cknitt added this pull request to stack #9093 October 27, 2026 19:58

cknitt requested a review from cristianoc October 27, 2026 20:18

cristianoc approved these changes Oct 28, 2026

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cknitt force-pushed the fix-9071-functor-hover branch from 518b1df to aac2e68 Compare October 28, 2026 07:58

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