[gjs: 2/3] CI: Compare cpplint and IWYU against the pull request's base branch

[Philip Chimento <pchimento src gnome org>]

commit d6772307601bae34aba95a073ae1d426bc361569
Author: Philip Chimento <philip chimento gmail com>
Date:   Wed Nov 25 15:20:21 2020 -0800

    CI: Compare cpplint and IWYU against the pull request's base branch
    
    Instead of always comparing against GNOME/gjs/master, try to find the
    place where the current branch was branched off of the upstream repository
    using an adaptation of the script that GLib uses.
    
    The main adaptation compared to GLib is that we are running on a
    lightweight image with sh and busybox, so we don't have fancy things like
    process redirection and diff formatting options.

 .gitlab-ci.yml  |  5 ++-
 test/test-ci.sh | 95 ++++++++++++++++++++++++++++++++++++---------------------
 2 files changed, 63 insertions(+), 37 deletions(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 210561b8..75a6c167 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -222,9 +222,8 @@ iwyu:
   stage: source_check
   image: registry.gitlab.gnome.org/gnome/gjs:fedora.mozjs78-debug
   script:
-    - git remote add upstream https://gitlab.gnome.org/GNOME/gjs || git remote set-url upstream 
https://gitlab.gnome.org/GNOME/gjs
-    - git fetch --depth=1 --no-tags upstream master
-    - ./tools/run_iwyu.sh upstream/master
+    - test/test-ci.sh UPSTREAM_BASE
+    - ./tools/run_iwyu.sh ci-upstream-base
   only:
     - branches
   except:
diff --git a/test/test-ci.sh b/test/test-ci.sh
index 67195288..c0ebe9ad 100755
--- a/test/test-ci.sh
+++ b/test/test-ci.sh
@@ -22,42 +22,58 @@ do_Set_Env () {
     export DISPLAY="${DISPLAY:-:0}"
 }
 
-do_Get_Upstream_Master () {
-    if test "$CI_PROJECT_PATH_SLUG" = "gnome-gjs"; then
-        if test "$CI_BUILD_REF_SLUG" = "master" -o \
-            "$CI_BUILD_REF_SLUG" = "gnome-"* -o \
-             -n "$CI_COMMIT_TAG"; then
-            echo '-----------------------------------------'
-            echo 'Running against upstream'
-            echo "=> $1 Nothing to do"
-
-            do_Done
-            exit 0
-        fi
-    fi
-
+do_Get_Upstream_Base () {
     echo '-----------------------------------------'
-    echo 'Cloning upstream master'
-
-    mkdir -p ~/tmp-upstream; cd ~/tmp-upstream || exit 1
-    git clone --branch master --no-tags --depth 1 https://gitlab.gnome.org/GNOME/gjs.git; cd gjs || exit 1
+    echo 'Finding common ancestor'
+
+    # We need to add a new remote for the upstream target branch, since this
+    # script could be running in a personal fork of the repository which has out
+    # of date branches.
+    #
+    # Limit the fetch to a certain date horizon to limit the amount of data we
+    # get. If the branch was forked from origin/master before this horizon, it
+    # should probably be rebased.
+    git remote add upstream https://gitlab.gnome.org/GNOME/gjs.git || \
+        git remote set-url upstream https://gitlab.gnome.org/GNOME/gjs.git
+    base_branch="${CI_MERGE_REQUEST_TARGET_BRANCH_NAME:-${CI_DEFAULT_BRANCH}}"
+    git fetch --shallow-since="14 days ago" --no-tags upstream "$base_branch"
+    git branch ci-upstream-base-branch FETCH_HEAD
+
+    # Work out the newest common ancestor between the detached HEAD that this CI
+    # job has checked out, and the upstream target branch (which will typically
+    # be `upstream/master` or `upstream/gnome-nn`).
+    #
+    # $CI_MERGE_REQUEST_TARGET_BRANCH_NAME is only defined if we’re running in a
+    # merge request pipeline; fall back to $CI_DEFAULT_BRANCH otherwise.
+    git rev-list --first-parent ci-upstream-base-branch | tac > base-revs.txt
+    git rev-list --first-parent HEAD | tac > head-revs.txt
+    newest_common_ancestor_sha=$(comm -12 base-revs.txt head-revs.txt | tail -1)
+    if test -z "$newest_common_ancestor_sha"; then
+        echo "Couldn’t find common ancestor with the upstream main branch. This"
+        echo "typically happens if you branched a long time ago. Please update"
+        echo "your clone, rebase, and re-push your branch."
+        exit 1
+    fi
+    echo "Merge base:"
+    git show --no-patch "$newest_common_ancestor_sha"
+    git branch -f ci-upstream-base "$newest_common_ancestor_sha"
     echo '-----------------------------------------'
 }
 
-do_Compare_With_Upstream_Master () {
+do_Compare_With_Upstream_Base () {
     echo '-----------------------------------------'
-    echo 'Compare the working code with upstream master'
+    echo 'Comparing the code with upstream merge base'
 
-    sort < /cwd/master-report.txt > /cwd/master-report-sorted.txt
-    sort < /cwd/current-report.txt > /cwd/current-report-sorted.txt
+    sort < /cwd/base-report.txt > /cwd/base-report-sorted.txt
+    sort < /cwd/head-report.txt > /cwd/head-report-sorted.txt
 
-    NEW_WARNINGS=$(comm -13 /cwd/master-report-sorted.txt /cwd/current-report-sorted.txt | wc -l)
-    REMOVED_WARNINGS=$(comm -23 /cwd/master-report-sorted.txt /cwd/current-report-sorted.txt | wc -l)
+    NEW_WARNINGS=$(comm -13 /cwd/base-report-sorted.txt /cwd/head-report-sorted.txt | wc -l)
+    REMOVED_WARNINGS=$(comm -23 /cwd/base-report-sorted.txt /cwd/head-report-sorted.txt | wc -l)
     if test "$NEW_WARNINGS" -ne 0; then
         echo '-----------------------------------------'
         echo "### $NEW_WARNINGS new warning(s) found by $1 ###"
         echo '-----------------------------------------'
-        diff -U0 /cwd/master-report.txt /cwd/current-report.txt || true
+        diff -U0 /cwd/base-report.txt /cwd/head-report.txt || true
         echo '-----------------------------------------'
         exit 1
     else
@@ -135,22 +151,33 @@ elif test "$1" = "CPPLINT"; then
     do_Print_Labels 'C/C++ Linter report '
 
     cpplint --quiet $(find . -name \*.cpp -or -name \*.c -or -name \*.h | sort) 2>&1 >/dev/null | \
-        tee "$save_dir"/analysis/current-report.txt | \
+        tee "$save_dir"/analysis/head-report.txt | \
         sed -E -e 's/:[0-9]+:/:LINE:/' -e 's/  +/ /g' \
-        > /cwd/current-report.txt
-    cat "$save_dir"/analysis/current-report.txt
+        > /cwd/head-report.txt
+    cat "$save_dir"/analysis/head-report.txt
     echo
 
-    # Get the code committed at upstream master
-    do_Get_Upstream_Master "cppLint"
+    do_Get_Upstream_Base
+    if test $(git rev-parse HEAD) = $(git rev-parse ci-upstream-base); then
+        echo '-----------------------------------------'
+        echo 'Running against upstream'
+        echo '=> cpplint: Nothing to do'
+        do_Done
+        exit 0
+    fi
+    git checkout ci-upstream-base
     cpplint --quiet $(find . -name \*.cpp -or -name \*.c -or -name \*.h | sort) 2>&1 >/dev/null | \
-        tee "$save_dir"/analysis/master-report.txt | \
+        tee "$save_dir"/analysis/base-report.txt | \
         sed -E -e 's/:[0-9]+:/:LINE:/' -e 's/  +/ /g' \
-        > /cwd/master-report.txt
+        > /cwd/base-report.txt
     echo
 
-    # Compare the report with master and fail if new warnings are found
-    do_Compare_With_Upstream_Master "cppLint"
+    # Compare the report with merge base and fail if new warnings are found
+    do_Compare_With_Upstream_Base "cpplint"
+
+elif test "$1" = "UPSTREAM_BASE"; then
+    do_Get_Upstream_Base
+    exit 0
 fi
 
 # Releases stuff and finishes