Change detection using git "three dot" diff (#35)

* Rework change detection via `git diff`

Previous implementation performed simple diff between two versions. New implementation fetches on demand more commits to have the merge base between two branches. Now it will detect only changes introduced by branch that was pushed, instead of mixing with changes introduced meanwhile on the base branch.

.github/workflows/pull-request-verification.yml

@@ -75,7 +75,12 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
-    - run: touch add.txt && rm README.md && echo "TEST" > LICENSE && git add -A
+    - name: configure GIT user
+      run: git config user.email "john@nowhere.local" && git config user.name "John Doe"
+    - name: modify working tree
+      run: touch add.txt && rm README.md && echo "TEST" > LICENSE
+    - name: commit changes
+      run: git add -A && git commit -a -m 'testing this action'
     - uses: ./
       id: filter
       with:

__tests__/git.test.ts

@@ -1,18 +1,11 @@
 import * as git from '../src/git'
-import {ExecOptions} from '@actions/exec'
 import {ChangeStatus} from '../src/file'
 
-describe('parsing of the git diff-index command', () => {
-  test('getChangedFiles returns files with correct change status', async () => {
-    const files = await git.getChangedFiles(git.FETCH_HEAD, (cmd, args, opts) => {
-      const stdout = opts?.listeners?.stdout
-      if (stdout) {
-        stdout(Buffer.from('A\u0000LICENSE\u0000'))
-        stdout(Buffer.from('M\u0000src/index.ts\u0000'))
-        stdout(Buffer.from('D\u0000src/main.ts\u0000'))
-      }
-      return Promise.resolve(0)
-    })
+describe('parsing output of the git diff command', () => {
+  test('parseGitDiffOutput returns files with correct change status', async () => {
+    const files = git.parseGitDiffOutput(
+      'A\u0000LICENSE\u0000' + 'M\u0000src/index.ts\u0000' + 'D\u0000src/main.ts\u0000'
+    )
     expect(files.length).toBe(3)
     expect(files[0].filename).toBe('LICENSE')
     expect(files[0].status).toBe(ChangeStatus.Added)

action.yml

@@ -17,15 +17,23 @@ inputs:
     required: false
   filters:
     description: 'Path to the configuration file or YAML string with filters definition'
-    required: false
+    required: true
   list-files:
     description: |
       Enables listing of files matching the filter:
         'none'  - Disables listing of matching files (default).
         'json'  - Matching files paths are serialized as JSON array.
         'shell' - Matching files paths are escaped and space-delimited. Output is usable as command line argument list in linux shell.
-    required: false
+    required: true
     default: none
+  initial-fetch-depth:
+    description: |
+      How many commits are initially fetched from base branch.
+      If needed, each subsequent fetch doubles the previously requested number of commits
+      until the merge-base is found or there are no more commits in the history.
+      This option takes effect only when changes are detected using git against different base branch.
+    required: false
+    default: '10'
 runs:
   using: 'node12'
   main: 'dist/index.js'