36958: _git: Fix recent commit completion descriptions.

The uniquifiers 'HEAD~$n' were incorrect when a recent commit was the second
parent of a merge commit.  Detect that case and print something correct
instead.

1 files changed, 29 insertions, 12 deletions

diff --git a/Completion/Unix/Command/_git b/Completion/Unix/Command/_git
index e38b1c6e7..279331b00 100644
--- a/Completion/Unix/Command/_git
+++ b/Completion/Unix/Command/_git
@@ -5650,6 +5650,8 @@ __git_recent_commits () {
   local i j k ret
   integer distance_from_head
   local label
+  local parents
+  local next_first_parent_ancestral_line_commit
 
   zparseopts -D -E O:=argument_array_names
   # Turn (-O foo:bar) to (foo bar)
@@ -5659,10 +5661,10 @@ __git_recent_commits () {
 
   # Careful: most %d will expand to the empty string.  Quote properly!
   # NOTE: we could use %D directly, but it's not available in git 1.9.1 at least.
-  commits=("${(f)"$(_call_program commits git --no-pager log $commit_opts -20 --format='%h%n%d%n%s\ \(%cr\)')"}")
+  commits=("${(f)"$(_call_program commits git --no-pager log $commit_opts -20 --format='%h%n%d%n%s\ \(%cr\)%n%p')"}")
   __git_command_successful $pipestatus || return 1
 
-  for i j k in "$commits[@]" ; do
+  for i j k parents in "$commits[@]" ; do
     # Note: the after-the-colon part must be unique across the entire array;
     # see workers/34768
     if (( $#commit_opts )); then
@@ -5671,20 +5673,35 @@ __git_recent_commits () {
       # description unique (due to workers/34768), which we do by including the
       # hash.  Git always prints enough hash digits to make the output unique.)
       label="[$i]"
-    elif (( distance_from_head == 0 )); then
-      label="[HEAD]   "
-    elif (( distance_from_head == 1 )); then
-      label="[HEAD^]  "
-    elif (( distance_from_head == 2 )); then
-      label="[HEAD^^] "
-    elif (( distance_from_head < 10 )); then
-      label="[HEAD~$distance_from_head] "
+    elif (( distance_from_head )) && [[ $i != $next_first_parent_ancestral_line_commit ]]; then
+      # The first commit (HEAD), and its ancestors along the first-parent line,
+      # get HEAD~$n labels.
+      #
+      # For other commits, we just print the hash.  (${parents} does provide enough
+      # information to compute HEAD~3^2~4 -style labels, though, if somebody cared
+      # enough to implement that.)
+      label="[$i]"
     else
-      label="[HEAD~$distance_from_head]"
+      # Compute a first-parent-ancestry commit's label.
+      if false ; then
+      elif (( distance_from_head == 0 )); then
+        label="[HEAD]   "
+      elif (( distance_from_head == 1 )); then
+        label="[HEAD^]  "
+      elif (( distance_from_head == 2 )); then
+        label="[HEAD^^] "
+      elif (( distance_from_head < 10 )); then
+        label="[HEAD~$distance_from_head] "
+      else
+        label="[HEAD~$distance_from_head]"
+      fi
+
+      # Prepare for the next first-parent-ancestry commit.
+      (( ++distance_from_head ))
+      next_first_parent_ancestral_line_commit=${parents%% *}
     fi
     # label is now 9 bytes, so the descriptions ($k) will be aligned.
     descr+=($i:"${label} $k")
-    (( ++distance_from_head ))
 
     j=${${j# \(}%\)} # strip leading ' (' and trailing ')'
     j=${j/ ->/,}  # Convert " -> master, origin/master".