editions: compiler disallows extension to have default value when file sets default presence to implicit

[jhump]

Extensions always have explicit presence. If an attempt is made to set the field_presence feature to IMPLICIT, the result is an error: "Extensions can't specify field presence".

Unfortunately, if the file default is set to IMPLICIT, protoc is acting as if the extension's field presence inherits this and does not allow setting a default value.

// test.proto
edition = "2023";
option features.field_presence = IMPLICIT;
message Extendee {
  extensions 1 to 2;
}
extend Extendee {
  uint32 ext_with_default = 1 [default = 123];
}

test.proto:8:10: Implicit presence fields can't specify defaults.

[mkruskal-google]

Nice, thanks for the thoroughness here Josh :)

[mkruskal-google]

This turned up a related issue: repeated closed enum fields are an error condition when they "inherit" IMPLICIT presence

[jhump]

This turned up a related issue: repeated closed enum fields are an error condition when they "inherit" IMPLICIT presence

Oh, interesting. I assume the intent is for both of these bugs to be fixed for the v27.0 release? I'll go ahead and test cases to protocompile in the meantime.

[mkruskal-google]

Yep, I'm changing the validation check to use has_presence (i.e. the actual computed behavior) instead of the resolved feature value