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`

1 files changed, 9 insertions, 10 deletions

diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index 6d94fe3ebb9..a59a0584d5e 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -3494,22 +3494,21 @@ impl<'test> TestCx<'test> {
         normalize_path(parent_dir, "$DIR");
 
         // Paths into the libstd/libcore
-        let src_dir = self
-            .config
-            .src_base
-            .parent()
-            .unwrap()
-            .parent()
-            .unwrap()
-            .parent()
-            .unwrap()
-            .join("library");
+        let base_dir = self.config.src_base.parent().unwrap().parent().unwrap().parent().unwrap();
+        let src_dir = base_dir.join("library");
         normalize_path(&src_dir, "$SRC_DIR");
 
+        // `ui-fulldeps` tests can show paths to the compiler source when testing macros from
+        // `rustc_macros`
+        // eg. /home/user/rust/compiler
+        let compiler_src_dir = base_dir.join("compiler");
+        normalize_path(&compiler_src_dir, "$COMPILER_DIR");
+
         if let Some(virtual_rust_source_base_dir) =
             option_env!("CFG_VIRTUAL_RUST_SOURCE_BASE_DIR").map(PathBuf::from)
         {
             normalize_path(&virtual_rust_source_base_dir.join("library"), "$SRC_DIR");
+            normalize_path(&virtual_rust_source_base_dir.join("compiler"), "$COMPILER_DIR");
         }
 
         // Paths into the build directory