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Changelog🐛 Bug fix
Semantic Diff1 commit · Full page ✏️ Compare constructor representations in interfaces and coercions alike594ff28 · cknitt + Claude · Oct 25, 2026, 06:54 UTC · edited
Diagnostic added (interface with an module M: {
type t = | @unboxed A(int) | B({x: int})
} = {
type t = | A(int) | B({x: int})
}
-none; clients read {TAG: "A", _0: 3} as B
+Type declarations do not match:
+ type t = A(int) | B({x: int})
+is not included in
+ type t = @unboxed A(int) | B({x: int})
+Their internal representations differ:
+case A is @unboxed only in the second declaration.Diagnostic added (coercion between representations) type a = | @unboxed A(int) | B({x: int})
type b = | A(int) | B({x: int}) | C
let x: b = (A(3): a :> b)
-none; the coerced 3 matches C
+Type a is not a subtype of bDiagnostic modified (unboxed configurations) @unboxed type x = One(bool) | Two
type y = One(bool) | Two
-- Variant x is not unboxed.
-- Variant y is unboxed.
+- Variant x is unboxed.
+- Variant y is not unboxed.Fixes #9038 |
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Codecov Report❌ Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## master #9039 +/- ##
=======================================
Coverage 81.32% 81.32%
=======================================
Files 456 456
Lines 64042 64046 +4
=======================================
+ Hits 52082 52087 +5
+ Misses 11960 11959 -1
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commit: |
Why:
An interface or a coercion accepted a tagged constructor for an
`@unboxed` one: inclusion compared only the tags of tagged constructors,
and the coercion check only the declared `@as` (#9038). The coercion
error also said that the wrong variant was unboxed.
`Variant_runtime.same_representation` compares two constructors: constant
with the same literal, tagged with the same tag, or both untagged. Interface
inclusion and the coercion check use it. Type declarations in messages print
the `@unboxed` of an untagged constructor of a type that is not `@unboxed`
itself, and an interface mismatch names the constructor that is `@unboxed`
in only one declaration. The predefined `unknown`, an
`@unboxed` variant, now has the untagged layout a declaration of it gets, so
`@unboxed type rec t = unknown = Unknown(_): t` still agrees with it.
Diagnostic added (interface with an @unboxed constructor):
Example:
module M: {
type t = | @unboxed A(int) | B({x: int})
} = {
type t = | A(int) | B({x: int})
}
Before (diagnostic): none; clients read {TAG: "A", _0: 3} as B
After (diagnostic):
Type declarations do not match:
type t = A(int) | B({x: int})
is not included in
type t = @unboxed A(int) | B({x: int})
Their internal representations differ:
case A is @unboxed only in the second declaration.
Diagnostic added (coercion between representations):
Example:
type a = | @unboxed A(int) | B({x: int})
type b = | A(int) | B({x: int}) | C
let x: b = (A(3): a :> b)
Before (diagnostic): none; the coerced 3 matches C
After (diagnostic):
Type a is not a subtype of b
Diagnostic modified (unboxed configurations):
Example:
@unboxed type x = One(bool) | Two
type y = One(bool) | Two
Before (diagnostic):
- Variant x is not unboxed.
- Variant y is unboxed.
After (diagnostic):
- Variant x is unboxed.
- Variant y is not unboxed.
Fixes #9038
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CMkrYaktctdKc4M41WF36t
Signed-off-by: Christoph Knittel <ck@cca.io>
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I think we better remove per-case unboxed.
It obviously never worked and is probably not needed anymore.
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Superseded by #9040, which removes |
Pull request was closed
Fixes #9038.
An interface or a coercion accepted a tagged constructor for an
@unboxedone. Interface inclusion compared only the tags of tagged constructors, and the coercion check only the declared@as, so a value built as{TAG: "A", _0: 3}was read by clients as another case.Variant_runtime.same_representationcompares two constructors at run time: both constant with the same literal, both tagged with the same tag, or both untagged.Includecore.compare_variantsand the coercion check inCtypeboth use it.Variant_coercion.variant_representation_matchesis gone.unknown, an@unboxedvariant, had a tagged layout. It now has the untagged layout that a declaration of it gets, so@unboxed type rec t = unknown = Unknown(_): tstill agrees with it.@unboxedof an untagged constructor when the type isn't@unboxedas a whole. Before, both sides of the mismatch printed astype t = A(int) | B({x: int}). The mismatch now says "case A is @unboxed only in the second declaration".@unboxedconfigurations named the wrong variant as unboxed. The existing snapshotvariant_to_variant_coercion_unboxedshowed this, and it is corrected.New tests: fixtures
untagged_constructor_interface_mismatch.resanduntagged_constructor_coercion_mismatch.res.Found by a review of the untagged variant work (#8950).
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https://claude.ai/code/session_01CMkrYaktctdKc4M41WF36t