output-parsing.md

Output Parsing

If you have a command or utility that you want to run pretty much as-is, but Trunk doesn't natively understand how to parse it, you can inject your own custom parser to translate its output into a format that Trunk does understand!

For example, let's say that we want to use grep as a linter, but we want to add more context to the matches. We could define a custom linter like so:

lint:
  definitions:
    - name: todo-finder
      files: [ALL]
      commands:
        - output: regex
          # matches the parser run output
          parse_regex: "((?P<path>.*):(?P<line>\\d+):(?P<col>\\d+): 
              \\[(?P<severity>.*)\\] (?P<message>.*) \\((?P<code>.*)\\))" 
          run: grep --with-filename --line-number --ignore-case todo ${target}
          success_codes: [0, 1]
          read_output_from: stdout
          parser:
            run:
              "sed -E 's/(.*):([0-9]+):(.*)/\\1:\\2:0: 
                 [error] Found todo in \"\\3\" (found-todo)/'"

The execution model that trunk follows for a parser is that it will:

• execute the linter's run field, asserting that either:
  • the linter's exit code is in success_codes, or
  • the linter's exit code is not in error_codes;
• execute parser.run,
  • with the read_output_from of the linter execution fed to parser.run as stdin,
  • assert that the exit code of the parser is 0, and then
• use output to determine how it should parse the parser's stdout.

Note that you can also set parser.runtime to node or python so that you can write your parser in Javascript or Python instead, if you so prefer! You can find plenty of examples of python parsers in our plugins repo.

{% tabs %} {% tab title="node" %} Node

lint:
  definitions:
    - name: todo-finder-node
      files: [ALL]
      commands:
        - output: parsable
          # parse_regex matches the parser run output
          parse_regex: "((?P<path>.*):(?P<line>\\d+):(?P<col>\\d+): 
              \\[(?P<severity>.*)\\] (?P<message>.*) \\((?P<code>.*)\\))" 
          run: grep --with-filename --line-number --ignore-case todo ${target}
          success_codes: [0, 1]
          read_output_from: stdout
          parser:
            runtime: node
            run: ${workspace}/todo-finder-parser.js

#!/usr/bin/env node
'use strict';
let readline = require('readline');
let rl = readline.createInterface({ input: process.stdin });

rl.on('line', function(line){
  let match = line.match(/(.*):([0-9]+):(.*)/);

  if (match) {
    let [_, path, line_number, line_contents] = match;
    console.log(`${path}:${line_number}:0: [error]`
            +` Found todo in "${line_contents}" (found-todo)`);
  }

Remember to run chmod u+x todo-finder-parser.js so that trunk can run it! {% endtab %}

{% tab title="python" %} Python

lint:
  definitions:
    - name: todo-finder-python
      files: [ALL]
      commands:
        - output: parsable
          # parse_regex matches the parser run output
          parse_regex: "((?P<path>.*):(?P<line>\\d+):(?P<col>\\d+): 
              \\[(?P<severity>.*)\\] (?P<message>.*) \\((?P<code>.*)\\))" 
          run: grep --with-filename --line-number --ignore-case todo ${target}
          success_codes: [0, 1]
          read_output_from: stdout
          parser:
            runtime: python
            run: ${workspace}/todo-finder-parser.js

#!/usr/bin/env python
import re, sys

for line in sys.stdin.readlines():
  match = re.match("(.*):([0-9]+):(.*)", line)
  if match:
    path, line_number, line_contents = match.groups()
    print(f"{path}:{line_number}:0: [error] "
           "Found todo in \"{line_contents}\" (found-todo)")

Remember to run chmod u+x todo-finder-parser.py so that trunk can run it! {% endtab %} {% endtabs %}