How to make the linter consider files only from the fork-point for a branch, rather than the current MASTER@HEAD?

[hacking-genie]

A common workflow with our repository is the following:

A dev will checkout at the main repository, and create a feature branch. This branch then will get pushed up and perhaps worked on a bit. Eventually it's set as a PR, but sometimes before it gets to this stage, the master branch will have moved ahead of the branch the PR is based on.

What seems to happen at this stage is that the PR is compared against the current master@head. Which means the Linter will end up looking at all the files that have been added/modified that come AFTER the feature branch ends. So we might end up linting files we don't want to.

Is there any way to fix this, so it only lints files we've modified in some way in the feature branch itself?

Here's my current configs...

.mega-linter.yml

APPLY_FIXES: none # all, none, or list of linter keys

ENABLE_LINTERS:
  - REPOSITORY_GIT_DIFF
  - EDITORCONFIG_EDITORCONFIG_CHECKER

DISABLE:
  - COPYPASTE # Comment to enable checks of excessive copy-pastes
  - SPELL # Comment to enable checks of spelling mistakes

SHOW_ELAPSED_TIME: true
FILEIO_REPORTER: false

github linter action yml

---
name: Linter

on:
  # Trigger mega-linter at every push. Action will also be visible from Pull Requests to master
  push: # Comment this line to trigger action only on pull-requests (not recommended if you don't pay for GH Actions)
  pull_request:
    branches: [develop]

env: # Comment env block if you do not want to apply fixes
  # Apply linter fixes configuration
  APPLY_FIXES: none # When active, APPLY_FIXES must also be defined as environment variable (in github/workflows/mega-linter.yml or other CI tool)
  APPLY_FIXES_EVENT: pull_request # Decide which event triggers application of fixes in a commit or a PR (pull_request, push, all)
  APPLY_FIXES_MODE: commit # If APPLY_FIXES is used, defines if the fixes are directly committed (commit) or posted in a PR (pull_request)

concurrency:
  group: ${{ github.ref }}-${{ github.workflow }}
  cancel-in-progress: true

jobs:
  build:
    name: MegaLinter
    runs-on: ubuntu-latest
    steps:
      # Git Checkout
      - name: Checkout Code
        uses: actions/checkout@v3
        with:
          token: ${{ secrets.PAT || secrets.GITHUB_TOKEN }}
          fetch-depth: 0 # If you use VALIDATE_ALL_CODEBASE = true, you can remove this line to improve performances

      # MegaLinter
      - name: MegaLinter
        id: ml
        uses: oxsecurity/megalinter/flavors/dotnet@v6 
        env:
          # All available variables are described in documentation
          # https://megalinter.io/configuration/
          VALIDATE_ALL_CODEBASE: ${{ github.event_name == 'push' && github.ref == 'refs/heads/develop' }} # Validates all source when push on develop, else just the git diff with develop. Set 'true' if you always want to lint all sources
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
          # ADD YOUR CUSTOM ENV VARIABLES HERE TO OVERRIDE VALUES OF .mega-linter.yml AT THE ROOT OF YOUR REPOSITORY

      # Upload MegaLinter artifacts
      - name: Archive production artifacts
        if: ${{ success() }} || ${{ failure() }}
        uses: actions/upload-artifact@v3
        with:
          name: MegaLinter reports
          path: |
            megalinter-reports
            mega-linter.log

      # Create pull request if applicable (for now works only on PR from same repository, not from forks)
      - name: Create Pull Request with applied fixes
        id: cpr
        if: steps.ml.outputs.has_updated_sources == 1 && (env.APPLY_FIXES_EVENT == 'all' || env.APPLY_FIXES_EVENT == github.event_name) && env.APPLY_FIXES_MODE == 'pull_request' && (github.event_name == 'push' || github.event.pull_request.head.repo.full_name == github.repository) && !contains(github.event.head_commit.message, 'skip fix')
        uses: peter-evans/create-pull-request@v4
        with:
          token: ${{ secrets.PAT || secrets.GITHUB_TOKEN }}
          commit-message: "[MegaLinter] Apply linters automatic fixes"
          title: "[MegaLinter] Apply linters automatic fixes"
          labels: bot
      - name: Create PR output
        if: steps.ml.outputs.has_updated_sources == 1 && (env.APPLY_FIXES_EVENT == 'all' || env.APPLY_FIXES_EVENT == github.event_name) && env.APPLY_FIXES_MODE == 'pull_request' && (github.event_name == 'push' || github.event.pull_request.head.repo.full_name == github.repository) && !contains(github.event.head_commit.message, 'skip fix')
        run: |
          echo "Pull Request Number - ${{ steps.cpr.outputs.pull-request-number }}"
          echo "Pull Request URL - ${{ steps.cpr.outputs.pull-request-url }}"

      # Push new commit if applicable (for now works only on PR from same repository, not from forks)
      - name: Prepare commit
        if: steps.ml.outputs.has_updated_sources == 1 && (env.APPLY_FIXES_EVENT == 'all' || env.APPLY_FIXES_EVENT == github.event_name) && env.APPLY_FIXES_MODE == 'commit' && github.ref != 'refs/heads/develop' && (github.event_name == 'push' || github.event.pull_request.head.repo.full_name == github.repository) && !contains(github.event.head_commit.message, 'skip fix')
        run: sudo chown -Rc $UID .git/
      - name: Commit and push applied linter fixes
        if: steps.ml.outputs.has_updated_sources == 1 && (env.APPLY_FIXES_EVENT == 'all' || env.APPLY_FIXES_EVENT == github.event_name) && env.APPLY_FIXES_MODE == 'commit' && github.ref != 'refs/heads/develop' && (github.event_name == 'push' || github.event.pull_request.head.repo.full_name == github.repository) && !contains(github.event.head_commit.message, 'skip fix')
        uses: stefanzweifel/git-auto-commit-action@v4
        with:
          branch: ${{ github.event.pull_request.head.ref || github.head_ref || github.ref }}
          commit_message: "[MegaLinter] Apply linters fixes"

[nvuillam]

I usually run linters on all files, in case it catches issues added in upgraded linter versions
Why wouldn't you want to analyze too many files ? ^^

[Kurt-von-Laven]

DEFAULT_BRANCH: develop # or whatever ref you want to base the Git diff against
VALIDATE_ALL_CODEBASE: false

[nvuillam]

Indeed, DEFAULT_BRANCH :)

[hacking-genie]

I usually run linters on all files, in case it catches issues added in upgraded linter versions Why wouldn't you want to analyze too many files ? ^^

There's a large existing repo, with many 3rd party bits of code, and so it'll be more noise than signal. I'd rather it focus on the code the dev is pushing up with their PR and we can focus on addressing old code + what to do with 3rd party stuff in its own initiative.

DEFAULT_BRANCH: develop # or whatever ref you want to base the Git diff against
VALIDATE_ALL_CODEBASE: false

Awesome, will give this a try, thanks!

[Kurt-von-Laven]

After rereading your post, you would actually need to push a tag of the branch point and use that tag as the DEFAULT_BRANCH. If you, understandably, aren't ecstatic about this prospect, you could run MegaLinter with DEFAULT_BRANCH: master on a clone of a clone. You would need to run git reset --hard "$(git merge-base --fork-point master HEAD)" on the intermediate clone to reset it to the state it was in at the time it was forked and ensure that the appropriate feature branch is checked out on the clone of the clone. Alternatively, you could require (e.g., via pre-push hook, traditional CI, and/or honor system) that folks always rebase prior to opening a (or pushing to an open) pull request, which is a good practice anyways. Another, not mutually exclusive option, in your situation is the megalinter-incremental pre-commit hook, which uses the --filesonly argument to mega-linter-runner to disable all linters that run in project mode (as opposed to individual files). You can run it only on the files being committed in that case, and it takes a lot of the load off your CI runners.