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Better error messages for GADTs and int overflows #7830

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Merged
merged 2 commits into from
Sep 3, 2025
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Merged

Better error messages for GADTs and int overflows #7830

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1701f12
Better error messages for GADTs and int overflows
fhammerschmidt Sep 2, 2025
40f90a7
Add test fixtures
fhammerschmidt Sep 2, 2025
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7 changes: 5 additions & 2 deletions compiler/frontend/bs_ast_invariant.ml
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Expand Up @@ -85,7 +85,9 @@ let emit_external_warnings : iterator =
( Nonrecursive,
[{ptype_kind = Ptype_variant ({pcd_res = Some _} :: _)}] ) ->
Location.raise_errorf ~loc:str_item.pstr_loc
"GADT has to be recursive types, please try `type rec'"
"GADTs require recursive type syntax.\n\
Please define your type using `type rec` instead of `type`.\n\
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I think we should avoid saying "please" here, we don't do that in other error messages either.

Example: type rec t = ..."
| _ -> super.structure_item self str_item);
expr =
(fun self ({pexp_loc = loc} as a) ->
Expand All @@ -95,7 +97,8 @@ let emit_external_warnings : iterator =
try ignore (Ext_string.hash_number_as_i32_exn s : int32)
with _ ->
Location.raise_errorf ~loc
"This number is too large to cause int overlow")
"Integer literal exceeds int32 range. Use float or BigInt if \
larger values are required.")
| _ -> super.expr self a);
label_declaration =
(fun self lbl ->
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16 changes: 16 additions & 0 deletions tests/build_tests/super_errors/expected/gadt_rec_missing.res.expected
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@@ -0,0 +1,16 @@

We've found a bug for you!
/.../fixtures/gadt_rec_missing.res:4:1-8:27

2 │ type daylight
3 │
4 │ type timezone<_> =
5 │  | EST: timezone<standard>
6 │  | EDT: timezone<daylight>
7 │  | CST: timezone<standard>
8 │  | CDT: timezone<daylight>
9 │

GADTs require recursive type syntax.
Please define your type using `type rec` instead of `type`.
Example: type rec t = ...
8 changes: 8 additions & 0 deletions tests/build_tests/super_errors/expected/polyvariant_int_too_large.res.expected
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@@ -0,0 +1,8 @@

We've found a bug for you!
/.../fixtures/polyvariant_int_too_large.res:1:9-29

1 │ let x = #12345678901234567890
2 │

Integer literal exceeds int32 range. Use float or BigInt if larger values are required.
8 changes: 8 additions & 0 deletions tests/build_tests/super_errors/fixtures/gadt_rec_missing.res
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@@ -0,0 +1,8 @@
type standard
type daylight

type timezone<_> =
| EST: timezone<standard>
| EDT: timezone<daylight>
| CST: timezone<standard>
| CDT: timezone<daylight>
1 change: 1 addition & 0 deletions tests/build_tests/super_errors/fixtures/polyvariant_int_too_large.res
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@@ -0,0 +1 @@
let x = #12345678901234567890
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