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[Sema] Disallow stored properties to have uninhabited types #19992

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Merged
merged 5 commits into from
Oct 26, 2018
Merged

[Sema] Disallow stored properties to have uninhabited types #19992

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7991aec
Disallow stored properties to have uninhabited types
Azoy Oct 23, 2018
f085c28
Not just instance members & better diagnostic
Azoy Oct 23, 2018
83e0cfa
Assert for unknown structurally uninhabited types
Azoy Oct 23, 2018
2973696
and generic enums aswell
Azoy Oct 24, 2018
5dcf823
Fix non instance member tests
Azoy Oct 24, 2018
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4 changes: 4 additions & 0 deletions include/swift/AST/DiagnosticsSema.def
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Expand Up @@ -1367,6 +1367,10 @@ ERROR(pattern_binds_no_variables,none,
"variables",
(unsigned))

ERROR(stored_property_no_uninhabited_type,none,
"stored property %0 cannot have uninhabited type %1",
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I don't love this diagnostic because I don't think "uninhabited" is a great user-facing term, but I can't think of anything really better.

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Yea, I was looking for ways to reword this, but I couldn't come up with anything.

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The compiler seems to define uninhabited types as either enums with no cases, or tuples containing uninhabited types. Could we just call it a "caseless enum" or "enum with no cases"? I suppose that might require a separate phrasing for tuples:

ERROR(stored_property_no_uninhabited_enum,none,
      "stored property %0 cannot have caseless enum %1", ...)
 ERROR(stored_property_no_uninhabited_tuple,none,
      "stored property %0 cannot have tuple type %1 containing caseless enum", ...)

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@Azoy Azoy Oct 23, 2018 •
edited
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How does this sound?

// Non-structurally
"%select{%select{variable|constant}0|property}1 %2 cannot have "
"enum type %3 with no cases"

// structurally
"%select{%select{variable|constant}0|property}1 %2 cannot have "
"tuple type %3 containing enum with no cases"

(Identifier, Type))

ERROR(nscoding_unstable_mangled_name,none,
"%select{private|fileprivate|nested|local}0 class %1 has an "
"unstable name when archiving via 'NSCoding'",
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9 changes: 9 additions & 0 deletions lib/Sema/TypeCheckDecl.cpp
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Expand Up @@ -2461,6 +2461,15 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
}
}

// Reject variable if it is a stored property with a structurally
// uninhabited type
if (VD->isInstanceMember() && VD->hasStorage() &&
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I don't think this is limited to members; any stored type properties or globals or even locals would have the same problem.

VD->getInterfaceType()->isStructurallyUninhabited()) {
TC.diagnose(VD->getLoc(), diag::stored_property_no_uninhabited_type,
VD->getName(), VD->getInterfaceType());
VD->markInvalid();
}

if (!checkOverrides(VD)) {
// If a property has an override attribute but does not override
// anything, complain.
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9 changes: 9 additions & 0 deletions test/decl/var/properties.swift
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Expand Up @@ -1267,3 +1267,12 @@ class WeakFixItTest {
// expected-error @+1 {{'weak' variable should have optional type '(WFI_P1 & WFI_P2)?'}} {{18-18=(}} {{33-33=)?}}
weak var bar : WFI_P1 & WFI_P2
}

// SR-8811
// Stored properties cannot have uninhabited types

struct SR8811 {
var x: Never // expected-error {{stored property 'x' cannot have uninhabited type 'Never'}}

var y: (Int, Never, Bool) // expected-error {{stored property 'y' cannot have uninhabited type '(Int, Never, Bool)'}}
}