Adjust prepare-commit-msg hook to arguments

<https://git-scm.com/docs/githooks#_prepare_commit_msg>

> It takes one to three parameters. The first is the name of the file
> that contains the commit log message. The second is the source of the
> commit message, and can be: ...  merge (if the commit is a merge or a
> .git/MERGE_MSG file exists) ...

1 files changed, 15 insertions, 17 deletions

diff --git a/git/template/hooks/prepare-commit-msg.awk b/git/template/hooks/prepare-commit-msg.awk
index d1c08c56..800e2220 100644..100755
--- a/git/template/hooks/prepare-commit-msg.awk
+++ b/git/template/hooks/prepare-commit-msg.awk
@@ -1,39 +1,37 @@
 # Filter to clean up a merge commit; still experimental on tejr's part.
 
-# If the first word of the subject line of the commit message is 'Merge', we
-# know we need to rewrite this; otherwise we can just bail out directly
-NR == 1 {
-    if (!(rewrite = ($1 == "Merge")))
+# If the second argument to this script is "merge", this is a merge commit, and
+# we know we need to filter it; otherwise we can just bail out directly
+BEGIN {
+    if (ARGV[2] != "merge")
         exit(0)
+    message = ARGV[1]
 }
 
-# We're starting a new branch; save the whole line into a variable and skip to
-# the next line
+# This line starts with an asterisk, so we're starting the commit listings for
+# a new branch; save the whole line into a variable and skip to the next line
 /^\* / {
     branch = $0
     next
 }
 
-# Skip this commit, it's just a version number bump
-# Other patterns to skip go HERE; be as precise as you can
-/^  Bump VERSION$/ { next }
+# Commit message subject patterns to skip go here; be as precise as you can
+$0 == "  Bump VERSION" { next }  # Skip version number bumps
 
 # If we got past this point, we have an actual commit line to include, so if
 # there's a branch heading yet to print, we should do so now; add it to the
 # line buffer
-length(branch) {
+branch {
     lines[++l] = branch
-    branch = ""
+    branch = 0
 }
 
 # Add the current line to the line buffer
 { lines[++l] = $0 }
 
-# When we get to the end of the file, we need to decide whether we're going to
-# rewrite the whole thing; note that the exit(0) call above still ends up down
-# here, so we have to check and set a flag
+# If we set the message filename in BEGIN due to this being a merge commit,
+# write our filtered message back to that file, and we're done
 END {
-    if (rewrite)
-        for (i = 1; i <= l; i++)
-            print lines[i] > ARGV[1]
+    for (i = 1; message && i <= l; i++)
+        print lines[i] > message
 }