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Fix bug conversions of function returning function failed #82398

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Fix bug conversions of function returning function failed #82398

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692d828
Add getNumCurryLevels() to AnyFunctionType
kntkymt Jun 22, 2025
e898bda
check curryLevels at repairByInsertingExplicitCall not to repair conv…
kntkymt Jun 22, 2025
0f98c1b
Add test for function-returning function conversion
kntkymt Jun 22, 2025
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11 changes: 11 additions & 0 deletions include/swift/AST/Types.h
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Original file line number Diff line number Diff line change
Expand Up @@ -3884,6 +3884,17 @@ class AnyFunctionType : public TypeBase {
return containsPackExpansionType(getParams());
}

/// Returns the number of curry levels of the function type.
unsigned getNumCurryLevels() const {
unsigned num = 1;
auto fn = this;
while (auto resultFn = fn->getResult()->getAs<AnyFunctionType>()) {
num++;
fn = resultFn;
}
return num;
}

static bool containsPackExpansionType(ArrayRef<Param> params);

static void printParams(ArrayRef<Param> Params, raw_ostream &OS,
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10 changes: 6 additions & 4 deletions lib/Sema/CSSimplify.cpp
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Expand Up @@ -5347,10 +5347,12 @@ bool ConstraintSystem::repairFailures(
// this by forming an explicit call.
auto convertTo = dstType->lookThroughAllOptionalTypes();

// If the RHS is a function type, the source must be a function-returning
// function.
if (convertTo->is<FunctionType>() && !resultType->is<FunctionType>())
return false;
// If the RHS is a function type,
// the source must have more curry levels.
if (auto convertToFnType = convertTo->getAs<FunctionType>()) {
if (fnType->getNumCurryLevels() <= convertToFnType->getNumCurryLevels())
return false;
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Sorry but I don't think this is the right fix. Before attempting this repair we need to make sure that there are no restrictions recorded (other locations in repairFailures do it with hasAnyRestriction) otherwise we end up in a situation like this where the fix is greedily applied before optional injection could be attempted (if that was allowed to proceed the types would line up exactly).

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Thanks for quick review!

we need to make sure that there are no restrictions recorded

I see, it sounds like related to the overall flow of reparingByInserting, it may be difficult for me to fix it 😅 let me close this PR and leave to owners 🙇 (Since I'm still a beginner of compiler)

}

// Right-hand side can't be a type variable or dependent member, or `Any`
// (if function conversion to `Any` didn't succeed there is something else
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11 changes: 11 additions & 0 deletions test/Constraints/closures.swift
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Expand Up @@ -1366,3 +1366,14 @@ do {
try $0.missing // expected-error {{value of type 'Int' has no member 'missing'}}
}
}

do {
let a: () -> () -> Void = {{}}
let _: (() -> () -> Void)? = a
let _: (() -> () -> Void)?? = a

class Super {}
class Sub: Super {}
let b: () -> () -> Sub = {{ return Sub() }}
let _: (() -> () -> Super)? = b
}