read-cache: pass 'repo' to 'ce_mode_from_stat()'

The ce_mode_from_stat() function is a performance-critical static
inline helper in 'read-cache.h'. As we migrate configuration
variables into the repository struct, this helper needs access
to the repository context.

Update the signature of ce_mode_from_stat() to take a 'struct
repository *' parameter, and update all callers to pass the
appropriate repository instance.

To prepare for the overhead of replacing cheap global variable
accesses with getter functions, the boolean expressions are
reordered to evaluate 'S_ISREG(mode)' first.

While at it, add a comment for ce_mode_from_stat().

Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: Ayush Chandekar <ayu.chandekar@gmail.com>
Mentored-by: Olamide Caleb Bello <belkid98@gmail.com>
Signed-off-by: Tian Yuchen <cat@malon.dev>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

apply.c

diff --git a/apply.c b/apply.c
index 249248d..26286eb 100644
--- a/apply.c
+++ b/apply.c
@@ -3894,7 +3894,7 @@ static int check_preimage(struct apply_state *state,
 			BUG("ce_mode == 0 for path '%s'", old_name);
 
 		if (trust_executable_bit || !S_ISREG(st->st_mode))
-			st_mode = ce_mode_from_stat(*ce, st->st_mode);
+			st_mode = ce_mode_from_stat(state->repo, *ce, st->st_mode);
 		else if (*ce)
 			st_mode = (*ce)->ce_mode;
 		else

builtin/update-index.c

diff --git a/builtin/update-index.c b/builtin/update-index.c
index 3d6646c..afd672a 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -294,7 +294,7 @@ static int add_one_path(const struct cache_entry *old, const char *path, int len
 	ce->ce_flags = create_ce_flags(0);
 	ce->ce_namelen = len;
 	fill_stat_cache_info(the_repository->index, ce, st);
-	ce->ce_mode = ce_mode_from_stat(old, st->st_mode);
+	ce->ce_mode = ce_mode_from_stat(the_repository, old, st->st_mode);
 
 	if (index_path(the_repository->index, &ce->oid, path, st,
 		       info_only ? 0 : INDEX_WRITE_OBJECT)) {

diff-lib.c

diff --git a/diff-lib.c b/diff-lib.c
index ae91027..46cae63 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -160,7 +160,7 @@ void run_diff_files(struct rev_info *revs, unsigned int option)
 
 			changed = check_removed(ce, &st);
 			if (!changed)
-				wt_mode = ce_mode_from_stat(ce, st.st_mode);
+				wt_mode = ce_mode_from_stat(revs->repo, ce, st.st_mode);
 			else {
 				if (changed < 0) {
 					perror(ce->name);
@@ -193,7 +193,7 @@ void run_diff_files(struct rev_info *revs, unsigned int option)
 					num_compare_stages++;
 					oidcpy(&dpath->parent[stage - 2].oid,
 					       &nce->oid);
-					dpath->parent[stage-2].mode = ce_mode_from_stat(nce, mode);
+					dpath->parent[stage-2].mode = ce_mode_from_stat(revs->repo, nce, mode);
 					dpath->parent[stage-2].status =
 						DIFF_STATUS_MODIFIED;
 				}
@@ -262,7 +262,7 @@ void run_diff_files(struct rev_info *revs, unsigned int option)
 				continue;
 			} else if (revs->diffopt.ita_invisible_in_index &&
 				   ce_intent_to_add(ce)) {
-				newmode = ce_mode_from_stat(ce, st.st_mode);
+				newmode = ce_mode_from_stat(revs->repo, ce, st.st_mode);
 				diff_addremove(&revs->diffopt, '+', newmode,
 					       null_oid(the_hash_algo), 0, ce->name, 0);
 				continue;
@@ -270,7 +270,7 @@ void run_diff_files(struct rev_info *revs, unsigned int option)
 
 			changed = match_stat_with_submodule(&revs->diffopt, ce, &st,
 							    ce_option, &dirty_submodule);
-			newmode = ce_mode_from_stat(ce, st.st_mode);
+			newmode = ce_mode_from_stat(revs->repo, ce, st.st_mode);
 		}
 
 		if (!changed && !dirty_submodule) {
@@ -338,7 +338,7 @@ static int get_stat_data(const struct cache_entry *ce,
 		changed = match_stat_with_submodule(diffopt, ce, &st,
 						    0, dirty_submodule);
 		if (changed) {
-			mode = ce_mode_from_stat(ce, st.st_mode);
+			mode = ce_mode_from_stat(diffopt->repo, ce, st.st_mode);
 			oid = null_oid(the_hash_algo);
 		}
 	}

read-cache.c

diff --git a/read-cache.c b/read-cache.c
index 1ced8c6..a9f0591 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -750,7 +750,7 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 		int pos = index_name_pos_also_unmerged(istate, path, namelen);
 
 		ent = (0 <= pos) ? istate->cache[pos] : NULL;
-		ce->ce_mode = ce_mode_from_stat(ent, st_mode);
+		ce->ce_mode = ce_mode_from_stat(istate->repo, ent, st_mode);
 	}
 
 	/* When core.ignorecase=true, determine if a directory of the same name but differing

read-cache.h

diff --git a/read-cache.h b/read-cache.h
index 043da1f..af8c657 100644
--- a/read-cache.h
+++ b/read-cache.h
@@ -4,15 +4,24 @@
 #include "read-cache-ll.h"
 #include "object.h"
 #include "pathspec.h"
+#include "environment.h"
 
-static inline unsigned int ce_mode_from_stat(const struct cache_entry *ce,
+/*
+ * Determine the appropriate index mode for a file based on its stat()
+ * information and the existing cache entry (if any).
+ *
+ * This function handles degradation for filesystems that lack
+ * symlink support or reliable executable bits.
+ */
+static inline unsigned int ce_mode_from_stat(struct repository *repo UNUSED,
+					     const struct cache_entry *ce,
 					     unsigned int mode)
 {
 	extern int trust_executable_bit, has_symlinks;
-	if (!has_symlinks && S_ISREG(mode) &&
+	if (S_ISREG(mode) && !has_symlinks &&
 	    ce && S_ISLNK(ce->ce_mode))
 		return ce->ce_mode;
-	if (!trust_executable_bit && S_ISREG(mode)) {
+	if (S_ISREG(mode) && !trust_executable_bit) {
 		if (ce && S_ISREG(ce->ce_mode))
 			return ce->ce_mode;
 		return create_ce_mode(0666);