Fix #296, Replace --first-parent with --ancestry-path

We used --first-parent for rev-list to avoid creating large tree.
In some cases the first parent will not include the start..stop commits.
Replacing this with --ancestry-path to get valid commits and also
added an extra check to avoid using multiple paths.

Author: grimmySwe

lib/git-subrepo

@@ -698,17 +698,30 @@ subrepo:branch() {
   local last_gitrepo_commit=
   local first_gitrepo_commit=
 
-  # TODO: Currently --first-parent avoids the branching
-  # Should you create a more complex structure instead?
   o "Subrepo parent: $subrepo_parent"
   if [[ -n "$subrepo_parent" ]]; then
     local prev_commit=
+    local ancestor=
     o "Create new commits with parents into the subrepo fetch"
-    OUT=true RUN git rev-list --reverse --first-parent "$subrepo_parent..HEAD"
+    OUT=true RUN git rev-list --reverse --ancestry-path "$subrepo_parent..HEAD"
     local commit_list="$output"
     for commit in $commit_list; do
       o "Working on $commit"
 
+      # Only include the commit if it's a child of the previous commit
+      # This way we create a single path between $subrepo_parent..HEAD
+      if [[ -n "$ancestor" ]]; then
+        local is_direct_child=$(git show -s --pretty=format:"%P" $commit | grep "$ancestor")
+        o "is child: $is_direct_child"
+        if [[ -z "$is_direct_child" ]]; then
+          o "Ignore $commit, it's not in the selected path"
+          continue
+        fi
+      fi
+
+      # Remember the previous commit from the parent repo path
+      ancestor="$commit"
+
       o "Find out the .gitrepo reference"
       FAIL=false OUT=true RUN git config --blob \
         "$commit":"$subdir/.gitrepo" "subrepo.commit"
@@ -717,7 +730,7 @@ subrepo:branch() {
       o "Check for rebase"
       if git:rev-exists "$refs_subrepo_fetch"; then
         if ! git:commit-in-rev-list  "$gitrepo_commit" "$refs_subrepo_fetch"; then
-          error "Can't branch: '$refs_subrepo_fetch' doesn't contain $gitrepo_commit."
+          error "Local repository does not contain $gitrepo_commit. Try to 'git subrepo fetch $subref' of add the '-F' flag to always fetch the latest content."
         fi
       fi
 

test/branch-rev-list-one-path.t

@@ -0,0 +1,43 @@
+#!/usr/bin/env bash
+
+set -e
+
+source test/setup
+
+use Test::More
+
+clone-foo-and-bar
+
+subrepo-clone-bar-into-foo
+
+(
+  cd $OWNER/foo
+  branchpoint=$(git rev-parse HEAD)
+  add-new-files bar/file1
+  add-new-files bar/file2
+  git checkout -b other $branchpoint
+  add-new-files bar/file3
+  add-new-files bar/file4
+  add-new-files bar/file5
+  git merge master
+) >& /dev/null || die
+
+test-exists "$OWNER/foo/bar/file1" "$OWNER/foo/bar/file2" "$OWNER/foo/bar/file3" "$OWNER/foo/bar/file4" "$OWNER/foo/bar/file5"
+
+is "$(
+  cd $OWNER/foo
+  git subrepo branch bar
+)" \
+  "Created branch 'subrepo/bar' and worktree '.git/tmp/subrepo/bar'." \
+  "subrepo branch command output is correct"
+
+is "$(
+  cd $OWNER/foo
+  git rev-list subrepo/bar | wc -l
+)" \
+  "6" \
+  "We have only created commits for one of the paths"
+
+done_testing
+
+teardown

test/branch-rev-list.t

@@ -0,0 +1,47 @@
+#!/usr/bin/env bash
+
+set -e
+
+source test/setup
+
+use Test::More
+
+clone-foo-and-bar
+
+subrepo-clone-bar-into-foo
+
+(
+  cd $OWNER/foo
+  branchpoint=$(git rev-parse HEAD)
+  add-new-files bar/file1
+  # We push here to force subrepo to handle
+  # histories where it's not first parent
+  git subrepo push bar
+  add-new-files bar/file2
+  git checkout -b other $branchpoint
+  add-new-files bar/file3
+  add-new-files bar/file4
+  add-new-files bar/file5
+  git merge master
+) >& /dev/null || die
+
+test-exists "$OWNER/foo/bar/file1" "$OWNER/foo/bar/file2" "$OWNER/foo/bar/file3" "$OWNER/foo/bar/file4" "$OWNER/foo/bar/file5"
+
+# -F is needed for branch to fetch new information
+is "$(
+  cd $OWNER/foo
+  git subrepo -F branch bar
+)" \
+  "Created branch 'subrepo/bar' and worktree '.git/tmp/subrepo/bar'." \
+  "subrepo branch command output is correct"
+
+is "$(
+  cd $OWNER/foo
+  git rev-list subrepo/bar | wc -l
+)" \
+  "5" \
+  "We have only created commits for one of the paths"
+
+done_testing
+
+teardown

test/branch.t

@@ -20,17 +20,21 @@ before="$(date -r $OWNER/foo/Foo '+%s')"
 
 save-original-state $OWNER/foo bar
 
+# Make sure that time stamps differ
+sleep 1
+
 is "$(
   cd $OWNER/foo
   git subrepo branch bar
 )" \
   "Created branch 'subrepo/bar' and worktree '.git/tmp/subrepo/bar'." \
   "subrepo branch command output is correct"
 
-sleep 1
+
 after="$(date -r $OWNER/foo/Foo '+%s')"
 assert-original-state $OWNER/foo bar
 
+# Check that we haven't checked out any temporary files
 is "$before" "$after" \
   "No modification on Foo"