real_path: remove unsafe API

Returning a shared buffer invites very subtle bugs due to reentrancy or
multi-threading, as demonstrated by the previous patch.

There was an unfinished effort to abolish this [1].

Let's finally rid of `real_path()`, using `strbuf_realpath()` instead.

This patch uses a local `strbuf` for most places where `real_path()` was
previously called.

However, two places return the value of `real_path()` to the caller. For
them, a `static` local `strbuf` was added, effectively pushing the
problem one level higher:
    read_gitfile_gently()
    get_superproject_working_tree()

[1] https://lore.kernel.org/git/1480964316-99305-1-git-send-email-bmwill@google.com/

Signed-off-by: Alexandr Miloslavskiy <alexandr.miloslavskiy@syntevo.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 7 deletions

diff --git a/abspath.c b/abspath.c
index 9857985329..d34026bfeb 100644
--- a/abspath.c
+++ b/abspath.c
@@ -206,12 +206,6 @@ error_out:
  * Resolve `path` into an absolute, cleaned-up path. The return value
  * comes from a shared buffer.
  */
-const char *real_path(const char *path)
-{
-	static struct strbuf realpath = STRBUF_INIT;
-	return strbuf_realpath(&realpath, path, 1);
-}
-
 const char *real_path_if_valid(const char *path)
 {
 	static struct strbuf realpath = STRBUF_INIT;
@@ -233,7 +227,7 @@ char *real_pathdup(const char *path, int die_on_error)
 
 /*
  * Use this to get an absolute path from a relative one. If you want
- * to resolve links, you should use real_path.
+ * to resolve links, you should use strbuf_realpath.
  */
 const char *absolute_path(const char *path)
 {