Fatal error: exception Whole_compiler.Ctype.Unify(_)

[chenglou]

Repro:

type nonrec 'label frame = {
  next: int }
type 'label t = {
  timeline: 'label frame array ;
  label: 'label }
let step person = { person with label = (ref person.label) }

Compiler output:

yarn run v1.9.4
$ bsb -make-world
[3/3] Building src/demo.cmj
FAILED: src/demo.cmj src/demo.cmi /Users/chenglou/Desktop/foo/src/demo.bs.js 
/Users/chenglou/.config/yarn/global/node_modules/bs-platform/lib/bsc.exe -nostdlib -bs-package-name foo  -bs-package-output commonjs:src -color always -bs-suffix -I src -I /Users/chenglou/Desktop/foo/node_modules/bs-platform/lib/ocaml -w -30-40+6+7+27+32..39+44+45+101 -warn-error +101  -o src/demo.cmj src/demo.mlast
Fatal error: exception Whole_compiler.Ctype.Unify(_)
Raised at file "ctype.ml", line 2797, characters 6-45
Called from file "typecore.ml", line 3016, characters 18-62
Called from file "array.ml", line 101, characters 21-40
Called from file "typecore.ml", line 3020, characters 36-68
Called from file "builtin_attributes.ml", line 165, characters 14-18
Re-raised at file "builtin_attributes.ml", line 170, characters 4-13
Called from file "typecore.ml", line 2610, characters 4-146
Called from file "typecore.ml", line 4584, characters 18-63
Called from file "list.ml", line 121, characters 32-39
Called from file "typecore.ml", line 4562, characters 4-1023
Called from file "typecore.ml", line 3722, characters 4-86
Called from file "builtin_attributes.ml", line 165, characters 14-18
Re-raised at file "builtin_attributes.ml", line 170, characters 4-13
Called from file "typecore.ml", line 2610, characters 4-146
Called from file "builtin_attributes.ml", line 165, characters 14-18
Re-raised at file "builtin_attributes.ml", line 170, characters 4-13
Called from file "list.ml", line 121, characters 32-39
Called from file "typecore.ml", line 4774, characters 4-1023
Called from file "typecore.ml", line 4851, characters 4-185
Called from file "typemod.ml", line 1426, characters 10-56
Called from file "typemod.ml", line 1653, characters 32-59
Called from file "typemod.ml", line 1657, characters 44-68
Called from file "typemod.ml", line 1657, characters 44-68
Called from file "typemod.ml", line 1665, characters 33-53
Called from file "builtin_attributes.ml", line 165, characters 14-18
Re-raised at file "builtin_attributes.ml", line 170, characters 4-13
Called from file "typemod.ml" (inlined), line 1685, characters 21-46
Called from file "typemod.ml", line 1788, characters 4-64
Re-raised at file "typemod.ml", line 1848, characters 4-11
Called from file "js_implementation.ml", line 170, characters 8-178
Called from file "arg.ml", line 261, characters 11-20
Called from file "arg.ml" (inlined), line 272, characters 2-84
Called from file "arg.ml" (inlined), line 276, characters 2-72
Called from file "arg.ml", line 281, characters 4-31
Called from file "js_main.ml", line 353, characters 4-49
Re-raised at file "location.ml", line 472, characters 14-25
Re-raised at file "location.ml", line 472, characters 14-25
Re-raised at file "location.ml", line 472, characters 14-25
Re-raised at file "location.ml", line 472, characters 14-25
Re-raised at file "location.ml", line 472, characters 14-25
Re-raised at file "location.ml", line 472, characters 14-25
Called from file "location.ml" (inlined), line 477, characters 31-61
Called from file "js_main.ml", line 357, characters 6-37
FAILED: subcommand failed.
error Command failed with exit code 2.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

Instead, it should correctly fail to type check (solution is to remove the ref in the last line)

[anmonteiro]

For what it's worth this is the utop output for your snippet:

type nonrec 'label frame = {
  next: int }
type 'label t = {
  timeline: 'label frame array ;
  label: 'label }
let step person = { person with label = (ref person.label) }
;;
Line 6, characters 18-60:
Error: This expression has type 'a ref t but an expression was expected of type
         'a t
       The type variable 'a occurs inside 'a ref

[bobzhang]

Do you see this in master? The stacktrace is intentional on master for debugging

[chenglou]

This is 7.0.0

[bobzhang]

bucklescript$ocamlc -c test.ml
Fatal error: exception Ctype.Unify(_)
bucklescript$ocamlc -v
The OCaml compiler, version 4.06.1
Standard library directory: /Users/hongbozhang/.opam/4.06.1/lib/ocaml

[bobzhang]

This is the same behavior as ocamlc@4.06.1, seems to be fixed in 4.08.1, will check if there is a easy cherry pick