Change fluent_messages macro to expect _ slugs instead of - slugs

For the most part, the macro actually worked with _ slugs, but the prefix_something -> prefix::something
conversion was not implemented.

We don't want to accept - slugs for consistency reasons.
We thus error if a name is found with - inside.
This ensures a consistent style.

compiler/rustc_macros/src/diagnostics/fluent.rs

@@ -189,13 +189,25 @@ pub(crate) fn fluent_messages(input: proc_macro::TokenStream) -> proc_macro::Tok
             if let Entry::Message(Message { id: Identifier { name }, attributes, .. }) = entry {
                 let _ = previous_defns.entry(name.to_string()).or_insert(ident_span);
 
-                // `typeck-foo-bar` => `foo_bar` (in `typeck.ftl`)
-                // `const-eval-baz` => `baz` (in `const_eval.ftl`)
+                if name.contains('-') {
+                    Diagnostic::spanned(
+                        ident_span,
+                        Level::Error,
+                        format!("name `{name}` contains a '-' character"),
+                    )
+                    .help("replace any '-'s with '_'s")
+                    .emit();
+                }
+
+                // `typeck_foo_bar` => `foo_bar` (in `typeck.ftl`)
+                // `const_eval_baz` => `baz` (in `const_eval.ftl`)
+                // `const-eval-hyphen-having` => `hyphen_having` (in `const_eval.ftl`)
+                // The last case we error about above, but we want to fall back gracefully
+                // so that only the error is being emitted and not also one about the macro
+                // failing.
                 let snake_name = Ident::new(
                     // FIXME: should probably trim prefix, not replace all occurrences
-                    &name
-                        .replace(&format!("{}-", res.ident).replace('_', "-"), "")
-                        .replace('-', "_"),
+                    &name.replace('-', "_").replace(&format!("{}_", res.ident), ""),
                     span,
                 );
                 constants.extend(quote! {
@@ -212,6 +224,16 @@ pub(crate) fn fluent_messages(input: proc_macro::TokenStream) -> proc_macro::Tok
                         continue;
                     }
 
+                    if attr_name.contains('-') {
+                        Diagnostic::spanned(
+                            ident_span,
+                            Level::Error,
+                            format!("attribute `{attr_name}` contains a '-' character"),
+                        )
+                        .help("replace any '-'s with '_'s")
+                        .emit();
+                    }
+
                     constants.extend(quote! {
                         pub const #snake_name: crate::SubdiagnosticMessage =
                             crate::SubdiagnosticMessage::FluentAttr(

src/test/ui-fulldeps/fluent-messages/label-with-hyphens.ftl

@@ -0,0 +1,2 @@
+some_slug = hi
+    .label-has-hyphens = test

src/test/ui-fulldeps/fluent-messages/slug-with-hyphens.ftl

@@ -0,0 +1 @@
+this-slug-has-hyphens = hi

src/test/ui-fulldeps/fluent-messages/test.rs

@@ -55,6 +55,24 @@ mod duplicate {
     }
 }
 
+mod slug_with_hyphens {
+    use super::fluent_messages;
+
+    fluent_messages! {
+        slug_with_hyphens => "./slug-with-hyphens.ftl",
+//~^ ERROR name `this-slug-has-hyphens` contains a '-' character
+    }
+}
+
+mod label_with_hyphens {
+    use super::fluent_messages;
+
+    fluent_messages! {
+        label_with_hyphens => "./label-with-hyphens.ftl",
+//~^ ERROR attribute `label-has-hyphens` contains a '-' character
+    }
+}
+
 mod valid {
     use super::fluent_messages;
 

src/test/ui-fulldeps/fluent-messages/test.stderr

@@ -41,5 +41,21 @@ help: previously defined in this resource
 LL |         a => "./duplicate-a.ftl",
    |         ^
 
-error: aborting due to 4 previous errors
+error: name `this-slug-has-hyphens` contains a '-' character
+  --> $DIR/test.rs:62:9
+   |
+LL |         slug_with_hyphens => "./slug-with-hyphens.ftl",
+   |         ^^^^^^^^^^^^^^^^^
+   |
+   = help: replace any '-'s with '_'s
+
+error: attribute `label-has-hyphens` contains a '-' character
+  --> $DIR/test.rs:71:9
+   |
+LL |         label_with_hyphens => "./label-with-hyphens.ftl",
+   |         ^^^^^^^^^^^^^^^^^^
+   |
+   = help: replace any '-'s with '_'s
+
+error: aborting due to 6 previous errors