warning: non-canonical string literal in `syntax` declaration
  --> testdata/parser/syntax/proto2_split.proto:15:10
   |
15 | syntax = "proto" "2";
   |          ^^^^^^^^^^^
  help: replace it with a canonical string
   |
15 | - syntax = "proto" "2";
15 | + syntax = "proto2";
   |
   = note: Protobuf implicitly concatenates adjacent string literals, like C or
           Python; this can lead to surprising behavior

encountered 1 warning
