Re: [RFC PATCH 2/4] Add alias option to git branch

[Kenneth Cochran <kenneth.cochran101@gmail.com>]

From 5aa6f037642df3b358ab659d17b5fb5bc7936f0f Mon Sep 17 00:00:00 2001
From: Kenneth Cochran <kenneth.cochran101@gmail.com>
Date: Sun, 3 Mar 2019 15:05:11 -0600
Subject: [RFC PATCH 2/4] refs: add function to iteratively dereference symref
 chain
Cc: Sahil Dua <sahildua2305@gmail.com>,
    Duy Nguyen <pclouds@gmail.com>,
    Jeff King <peff@peff.net>

As far as I can tell, currently, there's not really any way
to run something once per symref in a symref chain. This adds that
ability.

This will be useful for instance to improve how `git branch -d`
handles a checked out symref.

Signed-off-by: Kenneth Cochran <kenneth.cochran101@gmail.com>
---
 refs.c | 28 ++++++++++++++++++++++++++++
 refs.h | 13 +++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/refs.c b/refs.c
index 142888a40a..18a222d76a 100644
--- a/refs.c
+++ b/refs.c
@@ -1466,6 +1466,34 @@ static int do_for_each_ref(struct ref_store *refs, const char *prefix,
 					do_for_each_ref_helper, &hp);
 }
 
+int refs_for_each_ref_in_chain(struct ref_store *refs, each_ref_fn fn,
+			       void *cb_data, const char *starting_ref)
+{
+	int symref_count;
+	struct object_id oid;
+	int flags;
+	const char *ref_name = xstrdup(starting_ref);
+	int res;
+
+	for (symref_count = 0; symref_count < SYMREF_MAXDEPTH; symref_count++) {
+		res = fn(ref_name, &oid, flags, cb_data);
+		ref_name = refs_resolve_ref_unsafe(refs, ref_name, RESOLVE_REF_NO_RECURSE,
+						   &oid, &flags);
+
+		if (res)
+			return res;
+		if (!(flags & REF_ISSYMREF))
+			break;
+	}
+	return 0;
+}
+
+int for_each_ref_in_chain(each_ref_fn fn, void *cb_data, const char *starting_ref)
+{
+	return refs_for_each_ref_in_chain(get_main_ref_store(the_repository), fn,
+					  cb_data, starting_ref);
+}
+
 int refs_for_each_ref(struct ref_store *refs, each_ref_fn fn, void *cb_data)
 {
 	return do_for_each_ref(refs, "", fn, 0, 0, cb_data);
diff --git a/refs.h b/refs.h
index 308fa1f03b..66ccb85e8d 100644
--- a/refs.h
+++ b/refs.h
@@ -327,6 +327,19 @@ int for_each_glob_ref_in(each_ref_fn fn, const char *pattern,
 int head_ref_namespaced(each_ref_fn fn, void *cb_data);
 int for_each_namespaced_ref(each_ref_fn fn, void *cb_data);
 
+/*
+ * Iteratively calls fn with each reference in a symref chain.
+ * Iteration will continue until one of the following occurs:
+ * - SYMREF_MAXDEPTH is reached
+ * - A non-symbolic ref is reached (fn will be called with this before returning)
+ * - fn returns a non 0 value
+ *
+ * Will always return 0 unless fn returns a non-zero value.
+ */
+int refs_for_each_ref_in_chain(struct ref_store *refs, each_ref_fn fn,
+			       void *cb_data, const char *starting_ref);
+int for_each_ref_in_chain(each_ref_fn fn, void *cb_data, const char *starting_ref);
+
 /* can be used to learn about broken ref and symref */
 int refs_for_each_rawref(struct ref_store *refs, each_ref_fn fn, void *cb_data);
 int for_each_rawref(each_ref_fn fn, void *cb_data);
-- 
2.17.1