[PATCH] merge: use skip_prefix to parse config key

["Martin Ågren" <martin.agren@gmail.com>]

Instead of using `starts_with()`, the magic number 7, `strlen()` and a
fair number of additions to verify the three parts of the config key
"branch.<branch>.mergeoptions", use `skip_prefix()` to jump through them
more explicitly.

We need to introduce a new variable for this (we certainly can't modify
`k` just because we see "branch."!). With `skip_prefix()` we often use
quite bland names like `p` or `str`. Let's do the same. If and when this
function needs to do more prefix-skipping, we'll have a generic variable
ready for this.

Adjust the indentation while we're here.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
---

 worktree.c also matches "strcmp.*strlen" and could see a similar patch.
 I'm working on a longer series for that file and this fell out of that
 work. This feels independent enough that I'm posting it on its own.

 builtin/merge.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/builtin/merge.c b/builtin/merge.c
index d127d2225f..bde5f14f05 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -597,10 +597,10 @@ static void parse_branch_merge_options(char *bmo)
 static int git_merge_config(const char *k, const char *v, void *cb)
 {
 	int status;
+	const char *str;
 
-	if (branch && starts_with(k, "branch.") &&
-		starts_with(k + 7, branch) &&
-		!strcmp(k + 7 + strlen(branch), ".mergeoptions")) {
+	if (branch && skip_prefix(k, "branch.", &str) &&
+	    skip_prefix(str, branch, &str) && !strcmp(str, ".mergeoptions")) {
 		free(branch_mergeoptions);
 		branch_mergeoptions = xstrdup(v);
 		return 0;
-- 
2.26.0