read-cache: move 'ce_mode_from_stat()' to 'read-cache.c'

The ce_mode_from_stat() function is declared as a static inline function
in 'read-cache.h'. As we want to migrate configuration variables, this
helper function will need access to corresponding repository-specific
configuration logic. Move the implementation to 'read-cache.c' to
cleanly encapsulate its dependencies.

Note that the 'extern int trust_executable_bit, has_symlinks;' line is
discarded because it's not necessary when the function lives in
"read-cache.c".

At present, this change has no visible impact, but it is crucial
for our future plans to pass in the repo context. Comment
has been added whilst we are at it.

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>

Author: malon7782

read-cache.c

@@ -203,6 +203,19 @@ void fill_stat_cache_info(struct index_state *istate, struct cache_entry *ce, st
 	}
 }
 
+unsigned int ce_mode_from_stat(const struct cache_entry *ce, unsigned int mode)
+{
+	if (!has_symlinks && S_ISREG(mode) &&
+	    ce && S_ISLNK(ce->ce_mode))
+		return ce->ce_mode;
+	if (!trust_executable_bit && S_ISREG(mode)) {
+		if (ce && S_ISREG(ce->ce_mode))
+			return ce->ce_mode;
+		return create_ce_mode(0666);
+	}
+	return create_ce_mode(mode);
+}
+
 static unsigned int st_mode_from_ce(const struct cache_entry *ce)
 {
 	switch (ce->ce_mode & S_IFMT) {

read-cache.h

@@ -5,20 +5,15 @@
 #include "object.h"
 #include "pathspec.h"
 
-static inline unsigned int ce_mode_from_stat(const struct cache_entry *ce,
-					     unsigned int mode)
-{
-	extern int trust_executable_bit, has_symlinks;
-	if (!has_symlinks && S_ISREG(mode) &&
-	    ce && S_ISLNK(ce->ce_mode))
-		return ce->ce_mode;
-	if (!trust_executable_bit && S_ISREG(mode)) {
-		if (ce && S_ISREG(ce->ce_mode))
-			return ce->ce_mode;
-		return create_ce_mode(0666);
-	}
-	return create_ce_mode(mode);
-}
+/*
+ * 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.
+ */
+unsigned int ce_mode_from_stat(const struct cache_entry *ce,
+				unsigned int mode);
 
 static inline int ce_to_dtype(const struct cache_entry *ce)
 {