Improve various error messages #7500

zth · 2025-05-22T09:16:56Z

This explores how we can re-parse the relevant parts of the source where the error is, to give the viewer more concrete error messages (and suggestions for fixes) that we can't derive just from the type errors we see. It also improves a bunch of specific error messages:

Better JSX element mismatch messages (suggest how to convert int/float/string/array into Jsx.element)
Full rewrite suggestion for when passing an object to where a record is expected
Full rewrite suggestion when passing an array literal where a tuple is expected

zth · 2025-05-22T09:18:30Z

tests/build_tests/super_errors/expected/array_literal_passed_to_tuple.res.expected

+  [1;31mWe've found a bug for you![0m
+  [36m/.../fixtures/array_literal_passed_to_tuple.res[0m:[2m5:17-34[0m
+
+  3 [2m│[0m }
+  4 [2m│[0m 
+  [1;31m5[0m [2m│[0m let x = doStuff([1;31m["hello", "world"][0m)
+  6 [2m│[0m 
+
+  This has type: [1;31marray<'a>[0m
+  But it's expected to have type: [1;33m(string, string)[0m
+
+  - Fix this by passing a tuple instead of an array, like: [1;33m("hello", "world")
+[0m


When the user wrote an actual array literal, we can suggest the exact code for turning it into a tuple.

zth · 2025-05-22T09:18:54Z

tests/build_tests/super_errors/expected/array_var_passed_to_tuple.res.expected

+  [1;31mWe've found a bug for you![0m
+  [36m/.../fixtures/array_var_passed_to_tuple.res[0m:[2m7:17-18[0m
+
+  5 [2m│[0m let xx = ["hello", "world"]
+  6 [2m│[0m 
+  [1;31m7[0m [2m│[0m let x = doStuff([1;31mxx[0m)
+  8 [2m│[0m 
+
+  This has type: [1;31marray<string>[0m
+  But this function argument is expecting: [1;33m(string, string)[0m
+
+  - Fix this by passing a tuple instead of an array[1;33m[0m


When it's not an actual array literal, we just say that you need to pass a tuple instead.

zth · 2025-05-22T11:10:38Z

tests/build_tests/super_errors/expected/object_literal_passed_when_record_expected.res.expected

+  You're passing a [1;31mReScript object[0m where a [1;33mrecord[0m is expected. Objects are written with quoted keys, and records with unquoted keys.
+
+  Possible solutions: 
+  - Rewrite the object to a record, like: [1;33m{one: true}
+[0m


Another example of how we can suggest an actual and correct rewrite here, since we now have the relevant expression to look at.

this is great too! We could also do the same thing for mismatch of objects vs dicts now that we have dict literals, they could become quite common for configs.

zth · 2025-05-22T11:11:46Z

@mediremi @nojaf FYI, the work in this PR can probably serve as a good foundation for "compiler error message driven code actions" that we've been exploring before. Just need to figure out how to integrate it in a good way.

pkg-pr-new · 2025-05-22T11:25:47Z

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rescript

npm i https://pkg.pr.new/rescript-lang/rescript@7500

@rescript/darwin-x64

npm i https://pkg.pr.new/rescript-lang/rescript/@rescript/darwin-x64@7500

@rescript/linux-arm64

npm i https://pkg.pr.new/rescript-lang/rescript/@rescript/linux-arm64@7500

@rescript/darwin-arm64

npm i https://pkg.pr.new/rescript-lang/rescript/@rescript/darwin-arm64@7500

@rescript/win32-x64

npm i https://pkg.pr.new/rescript-lang/rescript/@rescript/win32-x64@7500

@rescript/linux-x64

npm i https://pkg.pr.new/rescript-lang/rescript/@rescript/linux-x64@7500

commit: 2f2dcb7

zth · 2025-05-22T12:39:21Z

compiler/bsc/rescript_compiler_main.ml

@@ -41,6 +69,7 @@ let process_file sourcefile ?kind ppf =
     properly
  *)
  setup_outcome_printer ();
+  Error_message_utils_support.setup ();


I think process_file is the appropriate place to run this, but maybe there's a better place, idk.

zth · 2025-05-22T12:47:20Z

@cknitt @tsnobip another round of error message feedback please! 😄

tsnobip

great work really @zth. We could also do the same thing for dicts now that we have dict literals that are kinda close to objects syntactically.

tsnobip · 2025-05-22T14:01:39Z

tests/build_tests/super_errors/expected/array_literal_passed_to_tuple.res.expected

+  [1;31mWe've found a bug for you![0m
+  [36m/.../fixtures/array_literal_passed_to_tuple.res[0m:[2m5:17-34[0m
+
+  3 [2m│[0m }
+  4 [2m│[0m 
+  [1;31m5[0m [2m│[0m let x = doStuff([1;31m["hello", "world"][0m)
+  6 [2m│[0m 
+
+  This has type: [1;31marray<'a>[0m
+  But it's expected to have type: [1;33m(string, string)[0m
+
+  - Fix this by passing a tuple instead of an array, like: [1;33m("hello", "world")
+[0m


tsnobip · 2025-05-22T14:02:27Z

tests/build_tests/super_errors/expected/jsx_type_mismatch_option.res.expected

+  You need to unwrap this option to its underlying value first, then turn that value into a JSX element.
+  For [1;33mNone[0m, you can use [1;33mReact.null[0m to output nothing into JSX.


this is nice because not obvious for newcomers!

tsnobip · 2025-05-22T14:03:28Z

tests/build_tests/super_errors/expected/object_literal_passed_when_record_expected.res.expected

+  You're passing a [1;31mReScript object[0m where a [1;33mrecord[0m is expected. Objects are written with quoted keys, and records with unquoted keys.
+
+  Possible solutions: 
+  - Rewrite the object to a record, like: [1;33m{one: true}
+[0m


this is great too! We could also do the same thing for mismatch of objects vs dicts now that we have dict literals, they could become quite common for configs.

zth · 2025-05-22T14:12:14Z

great work really @zth. We could also do the same thing for dicts now that we have dict literals that are kinda close to objects syntactically.

Oh, great idea.

cknitt

Awesome stuff!

tests/build_tests/super_errors/expected/math_operator_float.res.expected

zth · 2025-05-22T14:41:29Z

@tsnobip what error messages would you add for dicts?

tsnobip · 2025-05-22T15:02:52Z

@tsnobip what error messages would you add for dicts?

@zth Something like this when an object literal is provided but it should actually be a dict:

 You're passing a �[1;31mReScript object�[0m where a �[1;dict�[0m is expected. Dict literals start with dict{.

  Possible solutions: 
  - Rewrite the object to a dict, like: �[1;33mdict{"one": true}

zth · 2025-05-22T16:02:35Z

@zth Something like this when an object literal is provided but it should actually be a dict:

 You're passing a �[1;31mReScript object�[0m where a �[1;dict�[0m is expected. Dict literals start with dict{.

  Possible solutions: 
  - Rewrite the object to a dict, like: �[1;33mdict{"one": true}

The rewrite part is harder with dict since we need to make sure that they'd be compatible. But I guess some variant of it could be done. Might do it in a follow up though.

zth · 2025-05-22T16:06:07Z

@tsnobip did a basic one in: d2cac67

We can refine it later.

…ually wrote

zth commented May 22, 2025

View reviewed changes

zth force-pushed the tuple-error-message-improvement branch from 5163b5f to 131c0ed Compare May 22, 2025 10:37

zth commented May 22, 2025

View reviewed changes

zth changed the title ~~[WIP] Improve array <-> tuple error message~~ Improve various error messages May 22, 2025

zth commented May 22, 2025

View reviewed changes

zth requested review from cristianoc, cknitt and tsnobip May 22, 2025 12:46

zth marked this pull request as ready for review May 22, 2025 12:47

tsnobip approved these changes May 22, 2025

View reviewed changes

cknitt reviewed May 22, 2025

View reviewed changes

tests/build_tests/super_errors/expected/math_operator_float.res.expected Outdated Show resolved Hide resolved

zth enabled auto-merge (squash) May 22, 2025 16:15

zth added 9 commits May 22, 2025 18:17

improve array <-> tuple error message by looking at what the user act…

8b1ca40

…ually wrote

refactor

6a28ea9

example of detecting and providing rewrite for ReScript object -> record

a8378e6

remove Belt prefix

fa7e483

add dedicated JSX element type mismatch errors

991dfb6

note that you need to unwrap options in JSX

9f03508

fix

4f30225

add simple error message indicating dict syntax

aa1856a

changelog

2f2dcb7

zth force-pushed the tuple-error-message-improvement branch from 5c85e04 to 2f2dcb7 Compare May 22, 2025 16:17

zth merged commit 2193869 into master May 22, 2025
16 checks passed

zth deleted the tuple-error-message-improvement branch May 22, 2025 16:37

		You need to unwrap this option to its underlying value first, then turn that value into a JSX element.
		For [1;33mNone[0m, you can use [1;33mReact.null[0m to output nothing into JSX.

Improve various error messages #7500

Improve various error messages #7500

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