[PATCH 3/5] refspec: output a refspec item

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <dstolee@microsoft.com>

Add a new method, refspec_item_format(), that takes a 'struct
refspec_item' pointer as input and returns a string for how that refspec
item should be written to Git's config or a subcommand, such as 'git
fetch'.

There are several subtleties regarding special-case refspecs that can
occur and are represented in t5511-refspec.sh. These cases will be
explored in new tests in the following change. It requires adding a new
test helper in order to test this format directly, so that is saved for
a separate change to keep this one focused on the logic of the format
method.

A future change will consume this method when translating refspecs in
the 'prefetch' task of the 'git maintenance' builtin.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 refspec.c | 25 +++++++++++++++++++++++++
 refspec.h |  5 +++++
 2 files changed, 30 insertions(+)

diff --git a/refspec.c b/refspec.c
index e3d852c0bfec..ca65ba01bfe6 100644
--- a/refspec.c
+++ b/refspec.c
@@ -180,6 +180,31 @@ void refspec_item_clear(struct refspec_item *item)
 	item->exact_sha1 = 0;
 }
 
+const char *refspec_item_format(const struct refspec_item *rsi)
+{
+	static struct strbuf buf = STRBUF_INIT;
+
+	strbuf_reset(&buf);
+
+	if (rsi->matching)
+		return ":";
+
+	if (rsi->negative)
+		strbuf_addch(&buf, '^');
+	else if (rsi->force)
+		strbuf_addch(&buf, '+');
+
+	if (rsi->src)
+		strbuf_addstr(&buf, rsi->src);
+
+	if (rsi->dst) {
+		strbuf_addch(&buf, ':');
+		strbuf_addstr(&buf, rsi->dst);
+	}
+
+	return buf.buf;
+}
+
 void refspec_init(struct refspec *rs, int fetch)
 {
 	memset(rs, 0, sizeof(*rs));
diff --git a/refspec.h b/refspec.h
index 8b79891d3218..92a312f5b4e6 100644
--- a/refspec.h
+++ b/refspec.h
@@ -56,6 +56,11 @@ int refspec_item_init(struct refspec_item *item, const char *refspec,
 void refspec_item_init_or_die(struct refspec_item *item, const char *refspec,
 			      int fetch);
 void refspec_item_clear(struct refspec_item *item);
+/*
+ * Output a given refspec item to a string.
+ */
+const char *refspec_item_format(const struct refspec_item *rsi);
+
 void refspec_init(struct refspec *rs, int fetch);
 void refspec_append(struct refspec *rs, const char *refspec);
 __attribute__((format (printf,2,3)))
-- 
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