CI Build & Test: First build incrementally and test changed files only

.github/workflows/build.yml

@@ -29,24 +29,52 @@ jobs:
         id: checkout
         uses: actions/checkout@v3
 
-      - name: Prepare
+      - name: Update system packages
         id: prepare
         run: |
-          # Install test tools.
-          if apt-get update && apt-get install -y git python3-venv; then
-             # Debian-specific temporary code:
-             # Installation of python3-venv can be removed as soon as a
-             # base image with a release including #33822 is available
-             :
-          else
-             export PATH="build/bin:$PATH"
-             eval $(sage-print-system-package-command auto update)
-             eval $(sage-print-system-package-command auto --spkg --yes --no-install-recommends install git)
-          fi
+          export PATH="build/bin:$PATH"
+          eval $(sage-print-system-package-command auto update)
+          eval $(sage-print-system-package-command auto --spkg --yes --no-install-recommends install git)
+
+      - name: Incremental build and test
+        if: always() && steps.prepare.outcome == 'success'
+        id: incremental
+        run: |
+          set -ex
+          git config --global user.email "[email protected]"
+          git config --global user.name "Build & Test workflow"
+          # If actions/checkout downloaded our source tree using the GitHub REST API
+          # instead of with git (because do not have git installed in our image),
+          # we first make the source tree a repo.
+          if [ ! -d .git ]; then git config --global --add safe.directory $(pwd) && git init && git add -A && git commit --quiet -m "new"; fi
+          # Tag this state of the source tree "new". This is what we want to build and test.
+          git tag -f new
+          # Our container image contains a source tree in /sage with a full build of Sage.
+          # But /sage is not a git repository.
+          # We make /sage a worktree whose index is at tag "new".
+          # We then commit the current sources and set the tag "old". (This keeps all mtimes unchanged.)
+          # Then we update worktree and index with "git reset --hard".
+          # (This keeps mtimes of unchanged files unchanged and mtimes of changed files newer than unchanged files.)
+          # Finally we reset the index to "old". (This keeps all mtimes unchanged.)
+          # The changed files now show up as uncommitted changes.
+          git worktree add --detach worktree-image
+          rm -rf /sage/.git && mv worktree-image/.git /sage/
+          rm -rf worktree-image && ln -s /sage worktree-image
+          (cd worktree-image && git commit --allow-empty -m "old" -a && git tag -f old && git reset --hard new && git reset old)
+          # Now re-bootstrap and build. The build is incremental because we were careful with the timestamps.
+          # We run tests with "sage -t --new"; this only tests the uncommitted changes.
+          (cd worktree-image && ./bootstrap && make build && ./sage -t --new -p2)
+        env:
+          MAKE: make -j2
+          SAGE_NUM_THREADS: 2
+
+      - name: Configure new tree
+        if: always() && steps.prepare.outcome == 'success'
+        run: |
           # Reuse built SAGE_LOCAL contained in the Docker image 
           ./bootstrap
           ./configure --enable-build-as-root --prefix=/sage/local --with-sage-venv --enable-editable --enable-download-from-upstream-url
-      
+
       - name: Build and test modularized distributions
         if: always() && steps.prepare.outcome == 'success'
         run: make V=0 tox && make pypi-wheels
@@ -91,7 +119,7 @@ jobs:
         if: always() && steps.build.outcome == 'success'
         run: |
           ../sage -python -m pip install coverage
-          ../sage -python -m coverage run ./bin/sage-runtests --all -p2
+          ../sage -python -m coverage run ./bin/sage-runtests --all --long -p2
         working-directory: ./src
 
       - name: Prepare coverage results

src/sage/doctest/control.py

@@ -791,7 +791,7 @@ def add_files(self):
         # SAGE_ROOT_GIT can be None on distributions which typically
         # only have the SAGE_LOCAL install tree but not SAGE_ROOT
         if SAGE_ROOT_GIT is not None:
-            have_git = os.path.isdir(SAGE_ROOT_GIT)
+            have_git = os.path.exists(SAGE_ROOT_GIT)
         else:
             have_git = False