Better error messages for GADTs and int overflows (#7830)

fhammerschmidt · web-flow · commit 5cc393843b01 · 2025-09-03T08:33:08.000+02:00
* Better error messages for GADTs and int overflows

* Add test fixtures
diff --git a/compiler/frontend/bs_ast_invariant.ml b/compiler/frontend/bs_ast_invariant.ml
@@ -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\
+             Example: type rec t = ..."
         | _ -> super.structure_item self str_item);
     expr =
       (fun self ({pexp_loc = loc} as a) ->
@@ -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 ->
diff --git a/tests/build_tests/super_errors/expected/gadt_rec_missing.res.expected b/tests/build_tests/super_errors/expected/gadt_rec_missing.res.expected
@@ -0,0 +1,16 @@
+
+  [1;31mWe've found a bug for you![0m
+  [36m/.../fixtures/gadt_rec_missing.res[0m:[2m4:1-8:27[0m
+
+  2 [2m│[0m type daylight
+  3 [2m│[0m 
+  [1;31m4[0m [2m│[0m [1;31mtype timezone<_> =[0m
+  [1;31m5[0m [2m│[0m [1;31m  | EST: timezone<standard>[0m
+  [1;31m6[0m [2m│[0m [1;31m  | EDT: timezone<daylight>[0m
+  [1;31m7[0m [2m│[0m [1;31m  | CST: timezone<standard>[0m
+  [1;31m8[0m [2m│[0m [1;31m  | CDT: timezone<daylight>[0m
+  9 [2m│[0m 
+
+  GADTs require recursive type syntax.
+Please define your type using `type rec` instead of `type`.
+Example: type rec t = ...
diff --git a/tests/build_tests/super_errors/expected/polyvariant_int_too_large.res.expected b/tests/build_tests/super_errors/expected/polyvariant_int_too_large.res.expected
@@ -0,0 +1,8 @@
+
+  [1;31mWe've found a bug for you![0m
+  [36m/.../fixtures/polyvariant_int_too_large.res[0m:[2m1:9-29[0m
+
+  [1;31m1[0m [2m│[0m let x = [1;31m#12345678901234567890[0m
+  2 [2m│[0m 
+
+  Integer literal exceeds int32 range. Use float or BigInt if larger values are required.
diff --git a/tests/build_tests/super_errors/fixtures/gadt_rec_missing.res b/tests/build_tests/super_errors/fixtures/gadt_rec_missing.res
@@ -0,0 +1,8 @@
+type standard
+type daylight
+
+type timezone<_> =
+  | EST: timezone<standard>
+  | EDT: timezone<daylight>
+  | CST: timezone<standard>
+  | CDT: timezone<daylight>
diff --git a/tests/build_tests/super_errors/fixtures/polyvariant_int_too_large.res b/tests/build_tests/super_errors/fixtures/polyvariant_int_too_large.res
@@ -0,0 +1 @@
+let x = #12345678901234567890

-Original file line number
+Diff line change
@@ @@ -0,0 +1,16 @@ @@
++
 +  [1;31mWe've found a bug for you![0m
 +  [36m/.../fixtures/gadt_rec_missing.res[0m:[2m4:1-8:27[0m
++
 +  2 [2m│[0m type daylight
 +  3 [2m│[0m
 +  [1;31m4[0m [2m│[0m [1;31mtype timezone<_> =[0m
 +  [1;31m5[0m [2m│[0m [1;31m  | EST: timezone<standard>[0m
 +  [1;31m6[0m [2m│[0m [1;31m  | EDT: timezone<daylight>[0m
 +  [1;31m7[0m [2m│[0m [1;31m  | CST: timezone<standard>[0m
 +  [1;31m8[0m [2m│[0m [1;31m  | CDT: timezone<daylight>[0m
 +  9 [2m│[0m
++
 +  GADTs require recursive type syntax.
 +Please define your type using `type rec` instead of `type`.
 +Example: type rec t = ...