Always use G for EmissionGuarantee type variables.

That's what is mostly used. This commit changes a few `EM` and `E` and
`T` type variables to `G`.

Author: nnethercote

compiler/rustc_codegen_llvm/src/errors.rs

@@ -101,9 +101,9 @@ pub(crate) struct DynamicLinkingWithLTO;
 
 pub(crate) struct ParseTargetMachineConfig<'a>(pub LlvmError<'a>);
 
-impl<EM: EmissionGuarantee> IntoDiagnostic<'_, EM> for ParseTargetMachineConfig<'_> {
-    fn into_diagnostic(self, handler: &'_ Handler) -> DiagnosticBuilder<'_, EM> {
-        let diag: DiagnosticBuilder<'_, EM> = self.0.into_diagnostic(handler);
+impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for ParseTargetMachineConfig<'_> {
+    fn into_diagnostic(self, handler: &'_ Handler) -> DiagnosticBuilder<'_, G> {
+        let diag: DiagnosticBuilder<'_, G> = self.0.into_diagnostic(handler);
         let (message, _) = diag.styled_message().first().expect("`LlvmError` with no message");
         let message = handler.eagerly_translate_to_string(message.clone(), diag.args());
 
@@ -183,8 +183,8 @@ pub enum LlvmError<'a> {
 
 pub(crate) struct WithLlvmError<'a>(pub LlvmError<'a>, pub String);
 
-impl<EM: EmissionGuarantee> IntoDiagnostic<'_, EM> for WithLlvmError<'_> {
-    fn into_diagnostic(self, handler: &'_ Handler) -> DiagnosticBuilder<'_, EM> {
+impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for WithLlvmError<'_> {
+    fn into_diagnostic(self, handler: &'_ Handler) -> DiagnosticBuilder<'_, G> {
         use LlvmError::*;
         let msg_with_llvm_err = match &self.0 {
             WriteOutput { .. } => fluent::codegen_llvm_write_output_with_llvm_err,

compiler/rustc_errors/src/diagnostic_builder.rs

@@ -18,18 +18,18 @@ use std::thread::panicking;
 /// Trait implemented by error types. This should not be implemented manually. Instead, use
 /// `#[derive(Diagnostic)]` -- see [rustc_macros::Diagnostic].
 #[rustc_diagnostic_item = "IntoDiagnostic"]
-pub trait IntoDiagnostic<'a, T: EmissionGuarantee = ErrorGuaranteed> {
+pub trait IntoDiagnostic<'a, G: EmissionGuarantee = ErrorGuaranteed> {
     /// Write out as a diagnostic out of `Handler`.
     #[must_use]
-    fn into_diagnostic(self, handler: &'a Handler) -> DiagnosticBuilder<'a, T>;
+    fn into_diagnostic(self, handler: &'a Handler) -> DiagnosticBuilder<'a, G>;
 }
 
-impl<'a, T, E> IntoDiagnostic<'a, E> for Spanned<T>
+impl<'a, T, G> IntoDiagnostic<'a, G> for Spanned<T>
 where
-    T: IntoDiagnostic<'a, E>,
-    E: EmissionGuarantee,
+    T: IntoDiagnostic<'a, G>,
+    G: EmissionGuarantee,
 {
-    fn into_diagnostic(self, handler: &'a Handler) -> DiagnosticBuilder<'a, E> {
+    fn into_diagnostic(self, handler: &'a Handler) -> DiagnosticBuilder<'a, G> {
         let mut diag = self.node.into_diagnostic(handler);
         diag.set_span(self.span);
         diag

compiler/rustc_session/src/errors.rs

@@ -13,12 +13,12 @@ pub struct FeatureGateError {
     pub explain: DiagnosticMessage,
 }
 
-impl<'a, T: EmissionGuarantee> IntoDiagnostic<'a, T> for FeatureGateError {
+impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for FeatureGateError {
     #[track_caller]
     fn into_diagnostic(
         self,
         handler: &'a rustc_errors::Handler,
-    ) -> rustc_errors::DiagnosticBuilder<'a, T> {
+    ) -> rustc_errors::DiagnosticBuilder<'a, G> {
         let mut diag = handler.struct_diagnostic(self.explain);
         diag.set_span(self.span);
         diag.code(error_code!(E0658));