reviewdog fails to parse when `--server` option is given

[Masato Ohba]

Problem

When I run reviewdog/action-rubocopwith rubocop_flags: --server option, reviewdog command fails to parse its result.

 Running rubocop with reviewdog 🐶 ...
  reviewdog: parse error: failed to unmarshal rdjson (DiagnosticResult): proto: syntax error (line 1:1): invalid value RuboCop
  Error: Process completed with exit code 1.

Cause

rubocop with --server option always outputs server info, and it's not parsable for reviewdog.

$ rubocop ./test/rdjson_formatter/testdata/*.rb --require ./rdjson_formatter/rdjson_formatter.rb --format RdjsonFormatter --server
RuboCop server starting on 127.0.0.1:58694. # <= This line is not parsable.
{"source":{"name":"rubocop","url":"https://rubocop.org/"},"diagnostics":[{"message":"Missing frozen string literal comment.","location":{"path":"test/rdjson_formatter/testdata/correctable_offenses.rb","range":{"start":{"line":1,"column":1},"end":{"line":1,"column":2}}},"severity":"UNKNOWN_SEVERITY","code":{"value":"Style/FrozenStringLiteralComment"},"original_output":"C:  1:  1: Style/FrozenStringLiteralComment: Missing frozen string literal comment."},{"message":"Space missing after comma.","location":{"path":"test/rdjson_formatter/testdata/correctable_offenses.rb","range":{"start":{"line":1,"column":12},"end":{"line":1,"column":13}}},"severity":"UNKNOWN_SEVERITY","code":{"value":"Layout/SpaceAfterComma"},"original_output":"C:  1: 12: Layout/SpaceAfterComma: Space missing after comma."},{"message":"Unnecessary spacing detected.","location":{"path":"test/rdjson_formatter/testdata/correctable_offenses.rb","range":{"start":{"line":2,"column":4},"end":{"line":2,"column":7}}},"severity":"UNKNOWN_SEVERITY","code":{"value":"Layout/ExtraSpacing"},"original_output":"C:  2:  4: Layout/ExtraSpacing: Unnecessary spacing detected."},{"message":"Surrounding space missing for operator `+`.","location":{"path":"test/rdjson_formatter/testdata/correctable_offenses.rb","range":{"start":{"line":2,"column":13},"end":{"line":2,"column":14}}},"severity":"UNKNOWN_SEVERITY","code":{"value":"Layout/SpaceAroundOperators"},"original_output":"C:  2: 13: Layout/SpaceAroundOperators: Surrounding space missing for operator `+`."},{"message":"Unnecessary spacing detected.","location":{"path":"test/rdjson_formatter/testdata/correctable_offenses.rb","range":{"start":{"line":2,"column":14},"end":{"line":2,"column":16}}},"severity":"UNKNOWN_SEVERITY","code":{"value":"Layout/ExtraSpacing"},"original_output":"C:  2: 14: Layout/ExtraSpacing: Unnecessary spacing detected."},{"message":"Do not use semicolons to terminate expressions.","location":{"path":"test/rdjson_formatter/testdata/correctable_offenses.rb","range":{"start":{"line":2,"column":20},"end":{"line":2,"column":21}}},"severity":"UNKNOWN_SEVERITY","code":{"value":"Style/Semicolon"},"original_output":"C:  2: 20: Style/Semicolon: Do not use semicolons to terminate expressions."},{"message":"Redundant `return` detected.","location":{"path":"test/rdjson_formatter/testdata/correctable_offenses.rb","range":{"start":{"line":3,"column":3},"end":{"line":3,"column":9}}},"severity":"UNKNOWN_SEVERITY","code":{"value":"Style/RedundantReturn"},"original_output":"C:  3:  3: Style/RedundantReturn: Redundant `return` detected."},{"message":"Unnecessary spacing detected.","location":{"path":"test/rdjson_formatter/testdata/correctable_offenses.rb","range":{"start":{"line":3,"column":9},"end":{"line":3,"column":10}}},"severity":"UNKNOWN_SEVERITY","code":{"value":"Layout/ExtraSpacing"},"original_output":"C:  3:  9: Layout/ExtraSpacing: Unnecessary spacing detected."},{"message":"Empty file detected.","location":{"path":"test/rdjson_formatter/testdata/global_offenses.rb","range":{"start":{"line":1,"column":1},"end":{"line":1,"column":1}}},"severity":"UNKNOWN_SEVERITY","code":{"value":"Lint/EmptyFile"},"original_output":"W:  1:  1: Lint/EmptyFile: Empty file detected."},{"message":"Method parameter must be at least 3 characters long.","location":{"path":"test/rdjson_formatter/testdata/not_correctable_offenses.rb","range":{"start":{"line":4,"column":15},"end":{"line":4,"column":16}}},"severity":"UNKNOWN_SEVERITY","code":{"value":"Naming/MethodParameterName"},"original_output":"C:  4: 15: Naming/MethodParameterName: Method parameter must be at least 3 characters long."},{"message":"Method parameter must be at least 3 characters long.","location":{"path":"test/rdjson_formatter/testdata/not_correctable_offenses.rb","range":{"start":{"line":4,"column":18},"end":{"line":4,"column":19}}},"severity":"UNKNOWN_SEVERITY","code":{"value":"Naming/MethodParameterName"},"original_output":"C:  4: 18: Naming/MethodParameterName: Method parameter must be at least 3 characters long."},{"message":"Useless assignment to variable - `c`.","location":{"path":"test/rdjson_formatter/testdata/not_correctable_offenses.rb","range":{"start":{"line":5,"column":5},"end":{"line":5,"column":6}}},"severity":"UNKNOWN_SEVERITY","code":{"value":"Lint/UselessAssignment"},"original_output":"W:  5:  5: Lint/UselessAssignment: Useless assignment to variable - `c`."}]}

[Masato Ohba]

I found that there is no significant difference in speed whether in server mode or not for my application. So I'm closing this for now.