--start-at: Compare basenames if exact match failed

This more closely resembles the expected behaviour of --start-at, but
may lead to mismatches if several files in the filelist have the same
basename.

Closes #206

Related to #372 and #420

2 files changed, 56 insertions, 13 deletions

diff --git a/man/feh.pre b/man/feh.pre
index 173410e..e401ab5 100644
--- a/man/feh.pre
+++ b/man/feh.pre
@@ -729,20 +729,17 @@ to sort numbers naturally, so that e.g. 10.jpg comes after 2.jpg.
 Start the filelist at
 .Ar filename .
 .
-Note that at the moment,
+If you use relative paths in your filelist,
 .Ar filename
-must match an
-.Pq expanded
-path in the filelist.
-So, if the file to be matched is passed via an absolute path in the filelist,
-.Ar filename
-must be an absolute path.
-If the file is passed via a relative path,
-.Ar filename
-must be an identical relative path.
-This is a known issue.
-See also
-.Sx USAGE EXAMPLES .
+should also be a relative path.
+If you use absolute paths, it should also be an absolute path.
+.
+If
+.Nm
+cannot find an exact match, it will compare basenames
+.Pq filenames without the directory suffix .
+Note that this may lead to mismatches if several files in your filelist
+have the same basename.
 .
 .It Cm -T , --theme Ar theme
 .
diff --git a/src/slideshow.c b/src/slideshow.c
index 145bee1..145ced1 100644
--- a/src/slideshow.c
+++ b/src/slideshow.c
@@ -37,6 +37,24 @@ void init_slideshow_mode(void)
 	int success = 0;
 	gib_list *l = filelist, *last = NULL;
 
+	/*
+	 * In theory, --start-at FILENAME is simple: Look for a file called
+	 * FILENAME, start the filelist there, done.
+	 *
+	 * In practice, there are cases where this isn't sufficient. For instance,
+	 * a user running 'feh --start-at hello.jpg /tmp' will expect feh to start
+	 * at /tmp/hello.jpg, as if they had used
+	 * 'feh --start-at /tmp/hello.jpg /tmp'. Similarly, XDG Desktop files
+	 * may lead to the invocation 'feh --start-at /tmp/hello.jpg .' in /tmp,
+	 * expecting the behaviour of 'feh --start-at ./hello.jpg .'.
+	 *
+	 * Since a good user experience is not about being technically correct, but
+	 * about delivering the expected behaviour, we do some fuzzy matching
+	 * here. In the worst case, this will cause --start-at to start at the
+	 * wrong file.
+	 */
+
+	// Try finding an exact filename match first
 	for (; l && opt.start_list_at; l = l->next) {
 		if (!strcmp(opt.start_list_at, FEH_FILE(l->data)->filename)) {
 			opt.start_list_at = NULL;
@@ -44,6 +62,34 @@ void init_slideshow_mode(void)
 		}
 	}
 
+	/*
+	 * If it didn't work (opt.start_list_at is still set): Fall back to
+	 * comparing just the filenames without directory prefixes. This may lead
+	 * to false positives, but for now that's just the way it is.
+	 */
+	if (opt.start_list_at) {
+		char *current_filename;
+		char *start_at_filename = strrchr(opt.start_list_at, '/');
+		if (start_at_filename) {
+			start_at_filename++; // We only care about the part after the '/'
+		} else {
+			start_at_filename = opt.start_list_at;
+		}
+		for (l = filelist; l && opt.start_list_at; l = l->next) {
+			current_filename = strrchr(FEH_FILE(l->data)->filename, '/');
+			if (current_filename) {
+				current_filename++; // We only care about the part after the '/'
+			} else {
+				current_filename = FEH_FILE(l->data)->filename;
+			}
+			if (!strcmp(start_at_filename, current_filename)) {
+				opt.start_list_at = NULL;
+				break;
+			}
+		}
+	}
+
+	// If that didn't work either, we're out of luck.
 	if (opt.start_list_at)
 		eprintf("--start-at %s: File not found in filelist",
 				opt.start_list_at);