Fix overly general typeclass in generated type annotations#133
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dillonkearns wants to merge 1 commit intomdgriffith:mainfrom
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Fix overly general typeclass in generated type annotations#133dillonkearns wants to merge 1 commit intomdgriffith:mainfrom
dillonkearns wants to merge 1 commit intomdgriffith:mainfrom
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When a type variable stays polymorphic through an operator that requires a typeclass constraint (+ requires number, < requires comparable, ++ requires appendable), the constraint was lost during type variable rewriting, producing `a -> a -> a` instead of `number -> number -> number`. Root cause: `resolveVariables` replaces constrained names (like `number_0` or `comparable`) with arg variable names (like `arg_0`). Then `rewriteTypeVariables` renames `arg_0` to `a`, losing the constraint. Fix: `rewriteTypeVariablesPreservingConstraints` builds a mapping from resolved variable names back to their constraint names by walking the inference cache bidirectionally. If a constrained name maps to a generic (forward: `number_0 → arg_0`) or a generic maps to a constrained name (reverse: `arg_0 → comparable`), the constraint name is preserved during rewriting. Before: Elm.Op.plus a b → addBoth : a -> a -> a Elm.Op.lt a b → compareBoth : a -> a -> Bool Elm.Op.append a b → appendBoth : a -> a -> a After: Elm.Op.plus a b → addBoth : number -> number -> number Elm.Op.lt a b → compareBoth : comparable -> comparable -> Bool Elm.Op.append a b → appendBoth : appendable -> appendable -> appendable Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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| , test "number constraint with concrete: number -> number -> Float" <| | ||
| -- One arg is concrete (Float), the other stays polymorphic. | ||
| -- In Elm this is: number -> Float -> Float (the number unifies with Float) | ||
| \_ -> | ||
| Elm.Declare.fn2 "addToFloat" | ||
| (Arg.var "a") | ||
| (Arg.var "b") | ||
| (\a b -> Elm.Op.plus a (Elm.Op.plus b (Elm.float 1.0))) | ||
| |> .declaration | ||
| |> Elm.Expect.declarationAs | ||
| """ | ||
| addToFloat : Float -> Float -> Float | ||
| addToFloat a b = | ||
| a + (b + 1) | ||
| """ | ||
| , test "number constraint with one concrete Float arg" <| | ||
| -- When one arg is used with a Float literal, both args | ||
| -- resolve to Float (the number constraint narrows to Float) | ||
| \_ -> | ||
| Elm.Declare.fn2 "addToFloat" | ||
| (Arg.var "a") | ||
| (Arg.var "b") | ||
| (\a b -> Elm.Op.plus a (Elm.Op.plus b (Elm.float 1.0))) | ||
| |> .declaration | ||
| |> Elm.Expect.declarationAs | ||
| """ | ||
| addToFloat : Float -> Float -> Float | ||
| addToFloat a b = | ||
| a + (b + 1) | ||
| """ |
Contributor
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This seems to be the same test twice? I'm guessing one of them was supposed to test (a + b) + 1?
Contributor
|
Would love to see a compappend test too |
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Functions using
+,<, or++were incorrectly resulting in type annotations with plain type variables instead of constrained ones, producing code that doesn't compile.Example
Before (broken)
The Elm compiler rejects this:
After (fixed)
This applies to all three typeclass constraints:
Elm.Op.plus a ba -> a -> anumber -> number -> numberElm.Op.lt a ba -> a -> Boolcomparable -> comparable -> BoolElm.Op.append a ba -> a -> aappendable -> appendable -> appendableWhen one operand is concrete, the constraint correctly narrows: