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Document why no enum_extensibility is needed for Swift. (#5680)

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Document why no enum_extensibility is needed for Swift.
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Thomas Van Lenten 2019-02-05 13:10:44 -05:00 committed by GitHub
parent 6dcd81093c
commit 413c614a94
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1 changed files with 14 additions and 0 deletions
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14
src/google/protobuf/compiler/objectivec/objectivec_enum.cc
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@ -92,6 +92,20 @@ void EnumGenerator::GenerateHeader(io::Printer* printer) {
"\n",
"name", name_);
// Swift 5 included SE0192 "Handling Future Enum Cases"
// https://github.com/apple/swift-evolution/blob/master/proposals/0192-non-exhaustive-enums.md
// Since a .proto file can get new values added to an enum at any time, they
// are effectively "non-frozen". Even in a proto3 syntax file where there is
// support for the unknown value, an edit to the file can always add a new
// value moving something from unknown to known. Since Swift is now ABI
// stable, it also means a binary could contain Swift compiled against one
// version of the .pbobjc.h file, but finally linked against an enum with
// more cases. So the Swift code will always have to treat ObjC Proto Enums
// as "non-frozen". The default behavior in SE0192 is for all objc enums to
// be "non-frozen" unless marked as otherwise, so this means this generation
// doesn't have to bother with the `enum_extensibility` attribute, as the
// default will be what is needed.
printer->Print("$comments$typedef$deprecated_attribute$ GPB_ENUM($name$) {\n",
"comments", enum_comments,
"deprecated_attribute", GetOptionalDeprecatedAttribute(descriptor_, descriptor_->file()),