errors: improve error messages for cxx_file_stem and multiple dirs

Author: ahayzen-kdab

crates/cxx-qt-build/src/lib.rs

@@ -773,7 +773,11 @@ impl CxxQtBuilder {
                 })
                 .collect::<HashSet<String>>();
             if dirs.len() > 1 {
-                panic!("Only one directory is support per QmlModule for rust_files");
+                panic!(
+                    "Only one directory is supported per QmlModule for rust_files.\n\
+                    This is due to Qt bug https://bugreports.qt.io/browse/QTBUG-93443\n\
+                    Found directories: {dirs:?}"
+                );
             }
 
             for files in generate_cxxqt_cpp_files(

crates/cxx-qt-gen/src/parser/mod.rs

@@ -85,7 +85,7 @@ impl Parser {
                             } else if name_value.path.is_ident("cxx_file_stem") {
                                 return Err(Error::new(
                                     meta.span(),
-                                    "cxx_file_stem is unsupported: TODO new system message",
+                                    "cxx_file_stem is unsupported, instead the input file name will be used",
                                 ));
                             }
                         }