Add FIXMEs for some existing directive-handling concerns

Author: Zalathar

src/tools/compiletest/src/directives.rs

@@ -1462,6 +1462,8 @@ impl EditionRange {
 fn split_flags(flags: &str) -> Vec<String> {
     // Individual flags can be single-quoted to preserve spaces; see
     // <https://github.com/rust-lang/rust/pull/115948/commits/957c5db6>.
+    // FIXME(#147955): Replace this ad-hoc quoting with an escape/quote system that
+    // is closer to what actual shells do, so that it's more flexible and familiar.
     flags
         .split('\'')
         .enumerate()

src/tools/compiletest/src/directives/handlers.rs

@@ -81,6 +81,8 @@ fn make_directive_handlers_map() -> HashMap<&'static str, Handler> {
         handler(COMPILE_FLAGS, |config, ln, props| {
             if let Some(flags) = config.parse_name_value_directive(ln, COMPILE_FLAGS) {
                 let flags = split_flags(&flags);
+                // FIXME(#147955): Extract and unify this with other handlers that
+                // check compiler flags, e.g. MINICORE_COMPILE_FLAGS.
                 for (i, flag) in flags.iter().enumerate() {
                     if flag == "--edition" || flag.starts_with("--edition=") {
                         panic!("you must use `//@ edition` to configure the edition");
@@ -327,6 +329,8 @@ fn make_directive_handlers_map() -> HashMap<&'static str, Handler> {
         handler(MINICORE_COMPILE_FLAGS, |config, ln, props| {
             if let Some(flags) = config.parse_name_value_directive(ln, MINICORE_COMPILE_FLAGS) {
                 let flags = split_flags(&flags);
+                // FIXME(#147955): Extract and unify this with other handlers that
+                // check compiler flags, e.g. COMPILE_FLAGS.
                 for flag in &flags {
                     if flag == "--edition" || flag.starts_with("--edition=") {
                         panic!("you must use `//@ edition` to configure the edition");