Auto merge of #96853 - davidtwco:diagnostic-translation-unit-and-more-porting, r=oli-obk

diagnostics: port more diagnostics to derive + support for `()` fields

- Extend diagnostic derive so that spanless subdiagnostics (e.g. some uses of `help`/`note`) can be applied via attributes to fields of type `()` (currently spanless subdiagnostics are applied via attributes on the diagnostic struct itself). A consequence of this is that `Option<()>` fields can be used to represent optional spanless subdiagnostics, which are sometimes useful (e.g. for a `help` that should only show on nightly builds).
- Simplify the "explicit generic args with impl trait" diagnostic struct (from #96760) using support for `Option<()>` spanless subdiagnostics.
- Change `DiagnosticBuilder::set_arg`, used to provide context for Fluent messages, so that it takes anything that implements `IntoDiagnosticArg`, rather than `DiagnosticArgValue` - this improves the ergonomics of manual implementations of `SessionDiagnostic` which are translatable.
- Port "the type parameter `T` must be explicitly specified", "manual implementations of `X` are experimental", "could not resolve substs on overridden impl" diagnostics to diagnostic structs.
- When testing macros from `rustc_macros` in `ui-fulldeps` tests, sometimes paths from the compiler source tree can be shown in error messages - these need to be normalized in `compiletest`.

r? `@oli-obk`
cc `@pvdrz`

2 files changed, 4 insertions, 4 deletions

diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index 83e6a751394..909ed566f64 100644
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/compiler/rustc_errors/src/diagnostic.rs
@@ -821,9 +821,9 @@ impl Diagnostic {
     pub fn set_arg(
         &mut self,
         name: impl Into<Cow<'static, str>>,
-        arg: DiagnosticArgValue<'static>,
+        arg: impl IntoDiagnosticArg,
     ) -> &mut Self {
-        self.args.push((name.into(), arg));
+        self.args.push((name.into(), arg.into_diagnostic_arg()));
         self
     }
 
diff --git a/compiler/rustc_errors/src/diagnostic_builder.rs b/compiler/rustc_errors/src/diagnostic_builder.rs
index 96b730c2baa..53ad6e5a0ed 100644
--- a/compiler/rustc_errors/src/diagnostic_builder.rs
+++ b/compiler/rustc_errors/src/diagnostic_builder.rs
@@ -1,4 +1,4 @@
-use crate::diagnostic::DiagnosticArgValue;
+use crate::diagnostic::IntoDiagnosticArg;
 use crate::{Diagnostic, DiagnosticId, DiagnosticMessage, DiagnosticStyledString, ErrorGuaranteed};
 use crate::{Handler, Level, MultiSpan, StashKey};
 use rustc_lint_defs::Applicability;
@@ -528,7 +528,7 @@ impl<'a, G: EmissionGuarantee> DiagnosticBuilder<'a, G> {
     forward!(pub fn set_arg(
         &mut self,
         name: impl Into<Cow<'static, str>>,
-        arg: DiagnosticArgValue<'static>,
+        arg: impl IntoDiagnosticArg,
     ) -> &mut Self);
 
     forward!(pub fn subdiagnostic(