fish_indent: Print the failed files with --check

Also return the number of failed files.

I decided to *just* print the filenames (newline-separated because
NULLs are annoying here) to make it easier to deal with.

See #7251.

doc_src/cmds/fish_indent.rst

@@ -22,7 +22,7 @@ The following options are available:
 
 - ``-i`` or ``--no-indent`` do not indent commands; only reformat to one job per line.
 
-- ``-c`` or ``--check`` do not indent, only return 0 if the code is already indented as fish_indent would, 1 otherwise.
+- ``-c`` or ``--check`` do not indent, only return 0 if the code is already indented as fish_indent would, the number of failed files otherwise. Also print the failed filenames if not reading from stdin.
 
 - ``-v`` or ``--version`` displays the current fish version and then exits.
 

src/fish_indent.cpp

@@ -959,6 +959,8 @@ int main(int argc, char *argv[]) {
     argc -= optind;
     argv += optind;
 
+    int retval = 0;
+
     wcstring src;
     for (int i = 0; i < argc || (argc == 0 && i == 0); i++) {
         if (argc == 0 && i == 0) {
@@ -1028,7 +1030,10 @@ int main(int argc, char *argv[]) {
             }
             case output_type_check: {
                 if (output_wtext != src) {
-                    return 1;
+                    if (argc) {
+                        std::fwprintf(stderr, _(L"%s\n"), argv[i]);
+                    }
+                    retval++;
                 }
                 break;
             }
@@ -1036,5 +1041,5 @@ int main(int argc, char *argv[]) {
 
         std::fputws(str2wcstring(colored_output).c_str(), stdout);
     }
-    return 0;
+    return retval;
 }