Rollup merge of rust-lang#98428 - davidtwco:translation-derive-typed-…

…identifiers, r=oli-obk

macros: use typed identifiers in diag and subdiag derive

Using typed identifiers instead of strings with the Fluent identifiers in the diagnostic and subdiagnostic derives - this enables the diagnostic derive to benefit from the compile-time validation that comes with typed identifiers, namely that use of a non-existent Fluent identifier will not compile.

r? ```@oli-obk```

compiler/rustc_builtin_macros/src/cfg.rs

@@ -36,15 +36,15 @@ pub fn expand_cfg(
 }
 
 #[derive(SessionDiagnostic)]
-#[error(slug = "builtin-macros-requires-cfg-pattern")]
+#[error(builtin_macros::requires_cfg_pattern)]
 struct RequiresCfgPattern {
     #[primary_span]
     #[label]
     span: Span,
 }
 
 #[derive(SessionDiagnostic)]
-#[error(slug = "builtin-macros-expected-one-cfg-pattern")]
+#[error(builtin_macros::expected_one_cfg_pattern)]
 struct OneCfgPattern {
     #[primary_span]
     span: Span,

compiler/rustc_error_messages/locales/en-US/builtin_macros.ftl

@@ -1,5 +1,5 @@
-builtin-macros-requires-cfg-pattern =
+builtin_macros-requires-cfg-pattern =
     macro requires a cfg-pattern as an argument
     .label = cfg-pattern required
 
-builtin-macros-expected-one-cfg-pattern = expected 1 cfg-pattern
+builtin_macros-expected-one-cfg-pattern = expected 1 cfg-pattern

compiler/rustc_error_messages/src/lib.rs

@@ -258,18 +258,6 @@ pub enum SubdiagnosticMessage {
     FluentAttr(FluentId),
 }
 
-impl SubdiagnosticMessage {
-    /// Create a `SubdiagnosticMessage` for the provided Fluent attribute.
-    pub fn attr(id: impl Into<FluentId>) -> Self {
-        SubdiagnosticMessage::FluentAttr(id.into())
-    }
-
-    /// Create a `SubdiagnosticMessage` for the provided Fluent identifier.
-    pub fn message(id: impl Into<FluentId>) -> Self {
-        SubdiagnosticMessage::FluentIdentifier(id.into())
-    }
-}
-
 /// `From` impl that enables existing diagnostic calls to functions which now take
 /// `impl Into<SubdiagnosticMessage>` to continue to work as before.
 impl<S: Into<String>> From<S> for SubdiagnosticMessage {
@@ -332,11 +320,6 @@ impl DiagnosticMessage {
             _ => panic!("expected non-translatable diagnostic message"),
         }
     }
-
-    /// Create a `DiagnosticMessage` for the provided Fluent identifier.
-    pub fn new(id: impl Into<FluentId>) -> Self {
-        DiagnosticMessage::FluentIdentifier(id.into(), None)
-    }
 }
 
 /// `From` impl that enables existing diagnostic calls to functions which now take
@@ -347,6 +330,27 @@ impl<S: Into<String>> From<S> for DiagnosticMessage {
     }
 }
 
+/// Translating *into* a subdiagnostic message from a diagnostic message is a little strange - but
+/// the subdiagnostic functions (e.g. `span_label`) take a `SubdiagnosticMessage` and the
+/// subdiagnostic derive refers to typed identifiers that are `DiagnosticMessage`s, so need to be
+/// able to convert between these, as much as they'll be converted back into `DiagnosticMessage`
+/// using `with_subdiagnostic_message` eventually. Don't use this other than for the derive.
+impl Into<SubdiagnosticMessage> for DiagnosticMessage {
+    fn into(self) -> SubdiagnosticMessage {
+        match self {
+            DiagnosticMessage::Str(s) => SubdiagnosticMessage::Str(s),
+            DiagnosticMessage::FluentIdentifier(id, None) => {
+                SubdiagnosticMessage::FluentIdentifier(id)
+            }
+            // There isn't really a sensible behaviour for this because it loses information but
+            // this is the most sensible of the behaviours.
+            DiagnosticMessage::FluentIdentifier(_, Some(attr)) => {
+                SubdiagnosticMessage::FluentAttr(attr)
+            }
+        }
+    }
+}
+
 /// A span together with some additional data.
 #[derive(Clone, Debug)]
 pub struct SpanLabel {