This part of the official grammar unfortunately unclear; you may find Buf's
reverse engineering of the protobuf grammar to be more clear on this point
for your usecase: https://protobuf.com/docs/language-spec
On Saturday, October 21, 2023 at 11:43:45 AM UTC-4 Mattias Hansson wrote:
> I am currently trying to implement a protobuf parser but it's a bit
> unclear to me how I should interpret some parts of the specification.
>
> Lets start with RPC option. Options for normal fields and enum fields are
> pretty clear.
>
> Here's the specification for normal fields:
> field = [ "repeated" ] type fieldName "=" fieldNumber [ "[" fieldOptions
> "]" ] ";" fieldOptions = fieldOption { "," fieldOption } fieldOption =
> optionName "=" constant
>
> Here's the specification for enum fields:
> enum = "enum" enumName enumBody enumBody = "{" { option | enumField |
> emptyStatement | reserved } "}" enumField = ident "=" [ "-" ] intLit [
> "[" enumValueOption { "," enumValueOption } "]" ]";" enumValueOption =
> optionName "=" constant
>
> Both fields boils down to optionName which is specified as:
> optionName = ( ident | "(" ["."] fullIdent ")" )
> Here's the specification for RPC:
> service = "service" serviceName "{" { option | rpc | emptyStatement } "}" rpc
> = "rpc" rpcName "(" [ "stream" ] messageType ")" "returns" "(" [ "stream" ]
> messageType
> ")" (( "{" {option | emptyStatement } "}" ) | ";")
>
> RPC refers to plain option. Does this mean that the following is valid and
> intended syntax?
> rpc Foo (Req) returns (Res);
> rpc Foo (Req) returns (Res) {option opt1 = "opt1"; option opt2 = true; };
> rpc Foo (Req) returns (Res) {option opt1 = "opt1"; ;;; option opt2 = true;
> ;;;};
>
> I added number 3, because it seems like repetition is allowed together
> with emptyStatement. As a side note, I could not find any examples with RPC
> options as inspiration or to clear things up.
>
> Further, I also find the specification for optionName a bit unclear.
> Here's the specification for option and optionName:
> option = "option" optionName "=" constant ";" optionName = ( ident | "("
> ["."] fullIdent ")" )
> optionName does not seem to allow for repetition and fullIdent is only
> allowed within parenthesis(custom option). However multiple examples on
> https://protobuf.dev/programming-guides/proto3/#option-targets use
> custom-like options on the format:
> option (bar).baz = "value";
>
> For me it's pretty clear that the following optionNames are allowed:
> foo
> (foo)
> (foo.bar)
> (.foo)
> (.foo.bar)
>
> I don't really get which part of the specification that states that "baz",
> in the example above, is allowed outside of the parenthesis.
>
> Thanks in advance,
>
> /Mattias
>
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