File Browser: Avoid filling file cache needlessly on auto-complete

This would iterate over all files and call the sneaky `filelist_file()`,
meaning each file would be added to the cache for a minor query. That's
plenty of unnecessary work and kinda defeats the purpose of the partial
cache design.

source/blender/editors/space_file/filelist.cc

@@ -2201,11 +2201,15 @@ int filelist_file_find_id(const FileList *filelist, const ID *id)
   return -1;
 }
 
-ID *filelist_entry_get_id(const FileList *filelist, const int index)
+static FileListInternEntry *filelist_entry_intern_get(const FileList *filelist, const int index)
 {
   BLI_assert(index >= 0 && index < filelist->filelist.entries_filtered_num);
+  return filelist->filelist_intern.filtered[index];
+}
 
-  const FileListInternEntry *intern_entry = filelist->filelist_intern.filtered[index];
+ID *filelist_entry_get_id(const FileList *filelist, const int index)
+{
+  const FileListInternEntry *intern_entry = filelist_entry_intern_get(filelist, index);
   return intern_entry->local_data.id;
 }
 
@@ -2214,6 +2218,12 @@ ID *filelist_file_get_id(const FileDirEntry *file)
   return file->id;
 }
 
+const char *filelist_entry_get_relpath(const struct FileList *filelist, int index)
+{
+  const FileListInternEntry *intern_entry = filelist_entry_intern_get(filelist, index);
+  return intern_entry->relpath;
+}
+
 #define FILE_UID_UNSET 0
 
 static FileUID filelist_uid_generate(FileList *filelist)

source/blender/editors/space_file/filelist.h

@@ -144,6 +144,11 @@ struct ID *filelist_file_get_id(const struct FileDirEntry *file);
  * Same as #filelist_file_get_id(), but gets the file by index (doesn't require the file to be
  * cached, uses #FileListInternEntry only). */
 struct ID *filelist_entry_get_id(const struct FileList *filelist, int index);
+/**
+ * Get the #FileDirEntry.relpath value without requiring the #FileDirEntry to be available (doesn't
+ * require the file to be cached, uses #FileListInternEntry only).
+ */
+const char *filelist_entry_get_relpath(const struct FileList *filelist, int index);
 bool filelist_uid_is_set(const FileUID uid);
 void filelist_uid_unset(FileUID *r_uid);
 void filelist_file_cache_slidingwindow_set(struct FileList *filelist, size_t window_size);

source/blender/editors/space_file/filesel.cc

@@ -1194,13 +1194,13 @@ int file_select_match(struct SpaceFile *sfile, const char *pattern, char *matche
    * if the user selects a single file by entering the filename
    */
   for (int i = 0; i < n; i++) {
-    FileDirEntry *file = filelist_file(sfile->files, i);
+    const char *relpath = filelist_entry_get_relpath(sfile->files, i);
     /* Do not check whether file is a file or dir here! Causes: #44243
      * (we do accept directories at this stage). */
-    if (fnmatch(pattern, file->relpath, 0) == 0) {
-      filelist_entry_select_set(sfile->files, file, FILE_SEL_ADD, FILE_SEL_SELECTED, CHECK_ALL);
+    if (fnmatch(pattern, relpath, 0) == 0) {
+      filelist_entry_select_index_set(sfile->files, i, FILE_SEL_ADD, FILE_SEL_SELECTED, CHECK_ALL);
       if (!match) {
-        BLI_strncpy(matched_file, file->relpath, FILE_MAX);
+        BLI_strncpy(matched_file, relpath, FILE_MAX);
       }
       match++;
     }
@@ -1268,8 +1268,8 @@ int autocomplete_file(struct bContext *C, char *str, void * /*arg_v*/)
     int nentries = filelist_files_ensure(sfile->files);
 
     for (int i = 0; i < nentries; i++) {
-      FileDirEntry *file = filelist_file(sfile->files, i);
-      UI_autocomplete_update_name(autocpl, file->relpath);
+      const char *relpath = filelist_entry_get_relpath(sfile->files, i);
+      UI_autocomplete_update_name(autocpl, relpath);
     }
     match = UI_autocomplete_end(autocpl, str);
   }