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[cxx-interop] Synthesize a deprecated zero initializer for C++ structs #66220

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Merged
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Jun 1, 2023
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[cxx-interop] Synthesize a deprecated zero initializer for C++ structs #66220

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27 changes: 23 additions & 4 deletions lib/ClangImporter/ImportDecl.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2379,11 +2379,30 @@ namespace {
hasMemberwiseInitializer = false;
}

if (hasZeroInitializableStorage && !cxxRecordDecl) {
if (hasZeroInitializableStorage &&
!(cxxRecordDecl && cxxRecordDecl->hasDefaultConstructor())) {
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I wonder if we should limit this to C-looking C++ structs, e.g. those without base classes / templated parameters / etc.

// Add default constructor for the struct if compiling in C mode.
// If we're compiling for C++, we'll import the C++ default constructor
// (if there is one), so we don't need to synthesize one here.
ctors.push_back(synthesizer.createDefaultConstructor(result));
// If we're compiling for C++:
// 1. If a default constructor is declared, don't synthesize one.
// 2. If a default constructor is deleted, don't try to synthesize one.
// 3. If there is no default constructor, synthesize a C-like default
// constructor that zero-initializes the backing memory of the
// struct. This is important to maintain source compatibility when a
// client enables C++ interop in an existing project that uses C
// interop and might rely on the fact that C structs have a default
// constructor available in Swift.
ConstructorDecl *defaultCtor =
synthesizer.createDefaultConstructor(result);
ctors.push_back(defaultCtor);
if (cxxRecordDecl) {
auto attr = AvailableAttr::createPlatformAgnostic(
defaultCtor->getASTContext(),
"This zero-initializes the backing memory of the struct, which "
"is unsafe for some C++ structs. Consider adding an explicit "
"default initializer for this C++ struct.",
"", PlatformAgnosticAvailabilityKind::Deprecated);
defaultCtor->getAttrs().add(attr);
}
}

// We can assume that it is possible to correctly construct the object by
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4 changes: 0 additions & 4 deletions lib/ClangImporter/SwiftDeclSynthesizer.cpp
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Expand Up @@ -438,10 +438,6 @@ synthesizeStructDefaultConstructorBody(AbstractFunctionDecl *afd,
ASTContext &ctx = constructor->getASTContext();
auto structDecl = static_cast<StructDecl *>(context);

// We should call into C++ constructors directly.
assert(!isa<clang::CXXRecordDecl>(structDecl->getClangDecl()) &&
"Should not synthesize a C++ object constructor.");

// Use a builtin to produce a zero initializer, and assign it to self.

// Construct the left-hand reference to self.
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8 changes: 8 additions & 0 deletions test/Interop/Cxx/class/constructors-module-interface.swift
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Expand Up @@ -20,9 +20,13 @@
// CHECK-NEXT: }
// CHECK-NEXT: struct ConstructorWithParam {
// CHECK-NEXT: init(_ val: Int32)
// CHECK-NEXT: @available(*, deprecated, message
// CHECK-NEXT: init()
// CHECK-NEXT: var x: Int32
// CHECK-NEXT: }
// CHECK-NEXT: struct CopyAndMoveConstructor {
// CHECK-NEXT: @available(*, deprecated, message
// CHECK-NEXT: init()
// CHECK-NEXT: }
// CHECK-NEXT: struct Base {
// CHECK-NEXT: init()
Expand All @@ -38,10 +42,14 @@
// CHECK-NEXT: }
// CHECK: struct TemplatedConstructor {
// CHECK-NEXT: init<T>(_ value: T)
// CHECK-NEXT: @available(*, deprecated, message
// CHECK-NEXT: init()
// CHECK-NEXT: var value: ArgType
// CHECK-NEXT: }
// CHECK: struct TemplatedConstructorWithExtraArg {
// CHECK-NEXT: init<T>(_: Int32, _ value: T)
// CHECK-NEXT: init<T>(_ value: T, _: Int32)
// CHECK-NEXT: init<T, U>(_ value: T, _ other: U)
// CHECK-NEXT: @available(*, deprecated, message
// CHECK-NEXT: init()
// CHECK-NEXT: }
2 changes: 2 additions & 0 deletions test/Interop/Cxx/class/constructors-objc-module-interface.swift
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Expand Up @@ -7,4 +7,6 @@

// CHECK: struct ConstructorWithNSArrayParam {
// CHECK-NEXT: init(_ array: [Any]!)
// CHECK-NEXT: @available(*, deprecated, message
// CHECK-NEXT: init()
// CHECK-NEXT: }
2 changes: 1 addition & 1 deletion test/Interop/Cxx/class/constructors-typechecker.swift
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Expand Up @@ -6,7 +6,7 @@ let explicit = ExplicitDefaultConstructor()

let implicit = ImplicitDefaultConstructor()

let deletedImplicitly = ConstructorWithParam() // expected-error {{missing argument for parameter #1 in call}}
let deletedImplicitly = ConstructorWithParam() // expected-warning {{'init()' is deprecated}}

let deletedExplicitly = DefaultConstructorDeleted() // expected-error {{missing argument for parameter 'a' in call}}

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2 changes: 2 additions & 0 deletions test/Interop/Cxx/union/anonymous-union-partly-invalid-module-interface.swift
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Expand Up @@ -3,6 +3,8 @@
// CHECK: class C {
// CHECK-NEXT: }
// CHECK-NEXT: struct S {
// CHECK-NEXT: @available(*, deprecated, message
// CHECK-NEXT: init()
// CHECK-NEXT: mutating func f() -> Int32
// CHECK-NEXT: }
// CHECK-NEXT: func getSPtr() -> UnsafeMutablePointer<S>!