workflows: restrict coverage testing to changed packages

This commit improves the code-cover-gen workflow to only run tests for
the changed packages; other packages won't show up in the review so
coverage data is not useful. This should speed up the build
significantly.

.github/workflows/code-cover-gen.yaml

@@ -15,6 +15,7 @@ jobs:
     env:
       PR: ${{ github.event.pull_request.number }}
       HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+      GH_TOKEN: ${{ github.token }}
     steps:
       - uses: actions/checkout@v3
         with:
@@ -30,33 +31,38 @@ jobs:
         with:
           go-version: "1.20"
 
+      - name: Get list of changed packages
+        shell: bash
+        run: |
+          set -euxo pipefail
+          # To get the base commit, we get the number of commits in the PR.
+          # Note that github.event.pull_request.base.sha is not what we want,
+          # that is the tip of master and not necessarily the PR fork point.
+          NUM_COMMITS=$(gh pr view $PR --json commits --jq '.commits | length')
+          BASE_SHA=$(git rev-parse HEAD~${NUM_COMMITS})
+          CHANGED_PKGS=$(scripts/changed-go-pkgs.sh ${BASE_SHA} ${HEAD_SHA})
+          echo "BASE_SHA=${BASE_SHA}" >> "${GITHUB_ENV}"
+          echo "CHANGED_PKGS=${CHANGED_PKGS}" >> "${GITHUB_ENV}"
+
       - name: Generate "after" coverage
         shell: bash
         run: |
-          set -e
+          set -euxo pipefail
+          CHANGED_PKGS='${{ env.CHANGED_PKGS }}'
           mkdir -p artifacts
-          make testcoverage COVER_PROFILE=artifacts/cover-after.out
-          go run github.com/cockroachdb/code-cov-utils/gocover2json@latest \
-            --trim-prefix github.com/cockroachdb/pebble/ \
-            artifacts/cover-after.out artifacts/cover-${PR}-${HEAD_SHA}.json
+          # Make a copy of the script so that the "before" run below uses the
+          # same version.
+          cp scripts/pr-codecov-run-tests.sh ${RUNNER_TEMP}/
+          ${RUNNER_TEMP}/pr-codecov-run-tests.sh artifacts/cover-${PR}-${HEAD_SHA}.json "${CHANGED_PKGS}"
 
-      # Running the "before" coverage for each PR (rather than in a job that
-      # runs on push) is a little odd, but it allows restricting the packages on
-      # a per-PR basis (if it becomes necessary in the future).
       - name: Generate "before" coverage
         shell: bash
         run: |
-          set -e
-          # Note that github.event.pull_request.base.sha is not what we want -
-          # it is the current master tip, not the commit this PR is actually
-          # based on.
-          BASE_SHA=$(git merge-base origin/master ${HEAD_SHA})
+          set -euxo pipefail
+          BASE_SHA='${{ env.BASE_SHA }}'
+          CHANGED_PKGS='${{ env.CHANGED_PKGS }}'
           git checkout -f ${BASE_SHA}
-          make testcoverage COVER_PROFILE=artifacts/cover-before.out
-          SHA=$(git rev-parse HEAD)
-          go run github.com/cockroachdb/code-cov-utils/gocover2json@latest \
-            --trim-prefix github.com/cockroachdb/pebble/ \
-            artifacts/cover-before.out artifacts/cover-${PR}-${BASE_SHA}.json
+          ${RUNNER_TEMP}/pr-codecov-run-tests.sh artifacts/cover-${PR}-${BASE_SHA}.json "${CHANGED_PKGS}"
 
       - name: Upload artifacts
         uses: actions/upload-artifact@v2

scripts/changed-go-pkgs.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+
+BASE_SHA="$1"
+HEAD_SHA="$2"
+
+if [ -z "$HEAD_SHA" ];then
+    echo "Usage: $0 <base-sha> <head-sha>"
+    exit 1
+fi
+
+git diff --name-only "${BASE_SHA}..${HEAD_SHA}" -- "*.go" \
+  | xargs -rn1 dirname \
+  | sort -u \
+  | xargs echo

scripts/pr-codecov-run-tests.sh

@@ -0,0 +1,44 @@
+#!/usr/bin/env bash
+
+# This script runs unit tests with coverage enabled for a specific list of
+# package paths and outputs the coverage to a json file.
+#
+# Package paths that are not valid in this tree are tolerated.
+
+set -xeuo pipefail
+
+output_json_file="$1"
+packages="$2"
+
+# Find the targets. We need to convert from, e.g.
+#   . objstorage objstorage/objstorageprovider
+# to
+#   . ./objstorage ./objstorage/objstorageprovider
+
+paths=""
+sep=""
+
+for p in ${packages}; do
+  # Check that the path exists and contains Go files.
+  if ls "${p}"/*.go >/dev/null 2>&1; then
+    if [[ $p != "." ]]; then
+      p="./$p"
+    fi
+    paths="${paths}${sep}${p}"
+    sep=" "
+  fi
+done
+
+if [ -z "${paths}" ]; then
+  echo "Skipping"
+  touch "${output_json_file}"
+  exit 0
+fi
+
+tmpfile=$(mktemp --suffix -coverprofile)
+trap 'rm -f "${tmpfile}"' EXIT
+
+make testcoverage COVER_PROFILE="${tmpfile}" PKG="$paths"
+go run github.com/cockroachdb/code-cov-utils/[email protected] \
+  --trim-prefix github.com/cockroachdb/pebble/ \
+  "${tmpfile}" "${output_json_file}"