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[ConstraintSystem] Allow fixing missing conformance failures for Void and uninhabited types. #27123

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Merged
merged 4 commits into from
Sep 13, 2019
Merged

[ConstraintSystem] Allow fixing missing conformance failures for Void and uninhabited types. #27123

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b9367d1
[ConstraintSystem] Allow fixing missing conformance failures for
hborla Sep 11, 2019
85f3679
[Test] Add a simple test case for a method with an opaque return type
hborla Sep 11, 2019
911bcee
[Test] Update compiler_crashers_2_fixed/0196-rdar48937223.swift with new
hborla Sep 12, 2019
b2ec5b9
[Test] Update type_checker_crashers_fixed/rdar50869732.swift with mis…
hborla Sep 12, 2019
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5 changes: 0 additions & 5 deletions lib/Sema/CSSimplify.cpp
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Expand Up @@ -3971,11 +3971,6 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyConformsToConstraint(
return recordFix(fix) ? SolutionKind::Error : SolutionKind::Solved;
}

// Let's not try to fix missing conformance for Void
// or Never because that doesn't really make sense.
if (type->isVoid() || type->isUninhabited())
return SolutionKind::Error;

if (path.back().is<LocatorPathElt::AnyRequirement>()) {
// If this is a requirement associated with `Self` which is bound
// to `Any`, let's consider this "too incorrect" to continue.
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4 changes: 2 additions & 2 deletions test/Constraints/rdar44770297.swift
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Expand Up @@ -4,8 +4,8 @@ protocol P {
associatedtype A
}

func foo<T: P>(_: () throws -> T) -> T.A? { // expected-note {{in call to function 'foo'}}
func foo<T: P>(_: () throws -> T) -> T.A? { // expected-note {{where 'T' = 'Never'}}
fatalError()
}

let _ = foo() {fatalError()} & nil // expected-error {{generic parameter 'T' could not be inferred}}
let _ = foo() {fatalError()} & nil // expected-error {{global function 'foo' requires that 'Never' conform to 'P'}}
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This is a clear improvement!

However I can't help but wonder about 'Void'. The diagnostic would say "global function 'foo' requires that 'Void' conform to 'P'", which is a true statement, but 'Void' cannot ever conform to 'P'. Same if it's a function type or a metatype. As a follow-up you might want to add some test cases for non-nominal types and see if the diagnostic could be tailored a bit.

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I agree that there should be a tailored diagnostic. For example, this code:

protocol P {}

func genericFunc<T: P>(_ x: T) {}

genericFunc { return }

currently produces the error "Argument type '() -> ()' does not conform to expected type 'P'".

We already give a good error message for protocol types - "Protocol type 'P' cannot conform to 'P' because only concrete types can conform to protocols" - we could use a similar error message for non-nominal types.

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I'll do this in a separate PR

7 changes: 5 additions & 2 deletions test/type/opaque.swift
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Expand Up @@ -172,8 +172,11 @@ func recursion(x: Int) -> some P {
return recursion(x: x - 1)
}

// FIXME: We need to emit a better diagnostic than the failure to convert Never to opaque.
func noReturnStmts() -> some P { fatalError() } // expected-error{{cannot convert return expression of type 'Never' to return type 'some P'}} expected-error{{no return statements}}
func noReturnStmts() -> some P {} // expected-error {{function declares an opaque return type, but has no return statements in its body from which to infer an underlying type}}

func returnUninhabited() -> some P { // expected-note {{opaque return type declared here}}
fatalError() // expected-error{{return type of global function 'returnUninhabited()' requires that 'Never' conform to 'P'}}
}

func mismatchedReturnTypes(_ x: Bool, _ y: Int, _ z: String) -> some P { // expected-error{{do not have matching underlying types}}
if x {
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8 changes: 5 additions & 3 deletions validation-test/Sema/type_checker_crashers_fixed/rdar50869732.swift
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Expand Up @@ -10,7 +10,7 @@ struct Generic<T> {

@_functionBuilder
struct Builder {
static func buildBlock<C0, C1>(_ c0: C0, _ c1: C1)
static func buildBlock<C0, C1>(_ c0: C0, _ c1: C1) // expected-note {{where 'C0' = 'Empty'}} expected-note {{where 'C1' = 'Test<Empty>'}}
-> Generic<(C0, C1)> where C0 : P, C1 : P {
return Generic((c0, c1))
}
Expand All @@ -24,11 +24,13 @@ struct Empty {
init() {}
}

struct Test<T> where T : P {
struct Test<T> where T : P { // expected-note {{where 'T' = 'Empty'}}
init(@Builder _: () -> T) {}
}

let x = G {
// expected-error@-1 {{static method 'buildBlock' requires that 'Empty' conform to 'P'}}
// expected-error@-2 {{static method 'buildBlock' requires that 'Test<Empty>' conform to 'P'}}
Empty()
Test { <#code#> } // expected-error {{editor placeholder in source file}}
Test { Empty() } // expected-error {{generic struct 'Test' requires that 'Empty' conform to 'P'}}
}
4 changes: 2 additions & 2 deletions validation-test/compiler_crashers_2_fixed/0196-rdar48937223.swift
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Expand Up @@ -2,10 +2,10 @@

protocol P {}

func fn<T, U: P>(_ arg1: T, arg2: (T) -> U) {}
func fn<T, U: P>(_ arg1: T, arg2: (T) -> U) {} // expected-note {{where 'U' = '()'}}

func test(str: String) {
fn(str) { arg in
fn(str) { arg in // expected-error {{global function 'fn(_:arg2:)' requires that '()' conform to 'P'}}
<#FOO#> // expected-error {{editor placeholder in source file}}
}
}