[PATCH 05/19] replace-object: check_replace_refs is safe in multi repo environment

[Stefan Beller <sbeller@google.com>]

In e1111cef23 (inline lookup_replace_object() calls, 2011-05-15) a shortcut
for checking the object replacement was added by setting check_replace_refs
to 0 once the replacements were evaluated to not exist. This works fine in
with the assumption of only one repository in existence.

The assumption won't hold true any more when we work on multiple instances
of a repository structs (e.g. one struct per submodule), as the first
repository to be inspected may have no replacements and would set the
global variable. Other repositories would then completely omit their
evaluation of replacements.

This reverts back the meaning of the flag `check_replace_refs` of
"Do we need to check with the lookup table?" to "Do we need to read
the replacement definition?", adding the bypassing logic to
lookup_replace_object after the replacement definition was read.
As with the original patch, delay the renaming of the global variable

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 environment.c    | 2 +-
 replace-object.c | 2 --
 replace-object.h | 5 ++++-
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/environment.c b/environment.c
index 93c9fbb0ba..29f677c650 100644
--- a/environment.c
+++ b/environment.c
@@ -50,7 +50,7 @@ const char *editor_program;
 const char *askpass_program;
 const char *excludes_file;
 enum auto_crlf auto_crlf = AUTO_CRLF_FALSE;
-int check_replace_refs = 1;
+int check_replace_refs = 1; /* NEEDSWORK: rename to read_replace_refs */
 char *git_replace_ref_base;
 enum eol core_eol = EOL_UNSET;
 int global_conv_flags_eol = CONV_EOL_RNDTRP_WARN;
diff --git a/replace-object.c b/replace-object.c
index 603d11e931..c6d08c2e17 100644
--- a/replace-object.c
+++ b/replace-object.c
@@ -78,8 +78,6 @@ static void prepare_replace_object(void)
 
 	for_each_replace_ref(register_replace_ref, NULL);
 	the_repository->objects->replacements.prepared = 1;
-	if (!the_repository->objects->replacements.nr)
-		check_replace_refs = 0;
 }
 
 /* We allow "recursive" replacement. Only within reason, though */
diff --git a/replace-object.h b/replace-object.h
index 1e3e8805b9..f2555cddb9 100644
--- a/replace-object.h
+++ b/replace-object.h
@@ -3,6 +3,7 @@
 
 #include "cache.h"
 #include "repository.h"
+#include "object-store.h"
 
 struct replace_object {
 	unsigned char original[GIT_MAX_RAWSZ];
@@ -23,7 +24,9 @@ extern const unsigned char *do_lookup_replace_object(const unsigned char *sha1);
  */
 static inline const unsigned char *lookup_replace_object(const unsigned char *sha1)
 {
-	if (!check_replace_refs)
+	if (!check_replace_refs ||
+	    (the_repository->objects->replacements.prepared &&
+	     the_repository->objects->replacements.nr == 0))
 		return sha1;
 	return do_lookup_replace_object(sha1);
 }
-- 
2.17.0.484.g0c8726318c-goog