errors: only eagerly translate subdiagnostics

Subdiagnostics don't need to be lazily translated, they can always be
eagerly translated. Eager translation is slightly more complex as we need
to have a `DiagCtxt` available to perform the translation, which involves
slightly more threading of that context.

This slight increase in complexity should enable later simplifications -
like passing `DiagCtxt` into `AddToDiagnostic` and moving Fluent messages
into the diagnostic structs rather than having them in separate files
(working on that was what led to this change).

Signed-off-by: David Wood <david@davidtw.co>

1 files changed, 14 insertions, 22 deletions

diff --git a/compiler/rustc_error_messages/src/lib.rs b/compiler/rustc_error_messages/src/lib.rs
index a1abe8fd4f3..f91b6655f63 100644
--- a/compiler/rustc_error_messages/src/lib.rs
+++ b/compiler/rustc_error_messages/src/lib.rs
@@ -263,14 +263,10 @@ pub enum SubdiagnosticMessage {
     /// Translatable message which has already been translated eagerly.
     ///
     /// Some diagnostics have repeated subdiagnostics where the same interpolated variables would
-    /// be instantiated multiple times with different values. As translation normally happens
-    /// immediately prior to emission, after the diagnostic and subdiagnostic derive logic has run,
-    /// the setting of diagnostic arguments in the derived code will overwrite previous variable
-    /// values and only the final value will be set when translation occurs - resulting in
-    /// incorrect diagnostics. Eager translation results in translation for a subdiagnostic
-    /// happening immediately after the subdiagnostic derive's logic has been run. This variant
-    /// stores messages which have been translated eagerly.
-    Eager(Cow<'static, str>),
+    /// be instantiated multiple times with different values. These subdiagnostics' messages
+    /// are translated when they are added to the parent diagnostic, producing this variant of
+    /// `DiagnosticMessage`.
+    Translated(Cow<'static, str>),
     /// Identifier of a Fluent message. Instances of this variant are generated by the
     /// `Subdiagnostic` derive.
     FluentIdentifier(FluentId),
@@ -307,19 +303,15 @@ impl From<Cow<'static, str>> for SubdiagnosticMessage {
 pub enum DiagnosticMessage {
     /// Non-translatable diagnostic message.
     Str(Cow<'static, str>),
-    /// Translatable message which has already been translated eagerly.
+    /// Translatable message which has been already translated.
     ///
     /// Some diagnostics have repeated subdiagnostics where the same interpolated variables would
-    /// be instantiated multiple times with different values. As translation normally happens
-    /// immediately prior to emission, after the diagnostic and subdiagnostic derive logic has run,
-    /// the setting of diagnostic arguments in the derived code will overwrite previous variable
-    /// values and only the final value will be set when translation occurs - resulting in
-    /// incorrect diagnostics. Eager translation results in translation for a subdiagnostic
-    /// happening immediately after the subdiagnostic derive's logic has been run. This variant
-    /// stores messages which have been translated eagerly.
-    Eager(Cow<'static, str>),
+    /// be instantiated multiple times with different values. These subdiagnostics' messages
+    /// are translated when they are added to the parent diagnostic, producing this variant of
+    /// `DiagnosticMessage`.
+    Translated(Cow<'static, str>),
     /// Identifier for a Fluent message (with optional attribute) corresponding to the diagnostic
-    /// message.
+    /// message. Yet to be translated.
     ///
     /// <https://projectfluent.org/fluent/guide/hello.html>
     /// <https://projectfluent.org/fluent/guide/attributes.html>
@@ -336,7 +328,7 @@ impl DiagnosticMessage {
     pub fn with_subdiagnostic_message(&self, sub: SubdiagnosticMessage) -> Self {
         let attr = match sub {
             SubdiagnosticMessage::Str(s) => return DiagnosticMessage::Str(s),
-            SubdiagnosticMessage::Eager(s) => return DiagnosticMessage::Eager(s),
+            SubdiagnosticMessage::Translated(s) => return DiagnosticMessage::Translated(s),
             SubdiagnosticMessage::FluentIdentifier(id) => {
                 return DiagnosticMessage::FluentIdentifier(id, None);
             }
@@ -345,7 +337,7 @@ impl DiagnosticMessage {
 
         match self {
             DiagnosticMessage::Str(s) => DiagnosticMessage::Str(s.clone()),
-            DiagnosticMessage::Eager(s) => DiagnosticMessage::Eager(s.clone()),
+            DiagnosticMessage::Translated(s) => DiagnosticMessage::Translated(s.clone()),
             DiagnosticMessage::FluentIdentifier(id, _) => {
                 DiagnosticMessage::FluentIdentifier(id.clone(), Some(attr))
             }
@@ -354,7 +346,7 @@ impl DiagnosticMessage {
 
     pub fn as_str(&self) -> Option<&str> {
         match self {
-            DiagnosticMessage::Eager(s) | DiagnosticMessage::Str(s) => Some(s),
+            DiagnosticMessage::Translated(s) | DiagnosticMessage::Str(s) => Some(s),
             DiagnosticMessage::FluentIdentifier(_, _) => None,
         }
     }
@@ -396,7 +388,7 @@ impl Into<SubdiagnosticMessage> for DiagnosticMessage {
     fn into(self) -> SubdiagnosticMessage {
         match self {
             DiagnosticMessage::Str(s) => SubdiagnosticMessage::Str(s),
-            DiagnosticMessage::Eager(s) => SubdiagnosticMessage::Eager(s),
+            DiagnosticMessage::Translated(s) => SubdiagnosticMessage::Translated(s),
             DiagnosticMessage::FluentIdentifier(id, None) => {
                 SubdiagnosticMessage::FluentIdentifier(id)
             }