3 files changed, 48 insertions, 18 deletions
diff --git a/src/test/ui-fulldeps/session-diagnostic/diagnostic-derive.rs b/src/test/ui-fulldeps/session-diagnostic/diagnostic-derive.rs
index c63410fa35b..1cdc5d18c28 100644
--- a/src/test/ui-fulldeps/session-diagnostic/diagnostic-derive.rs
+++ b/src/test/ui-fulldeps/session-diagnostic/diagnostic-derive.rs
@@ -327,7 +327,7 @@ struct ErrorWithDefaultLabelAttr<'a> {
 }
 
 #[derive(SessionDiagnostic)]
-//~^ ERROR no method named `into_diagnostic_arg` found for struct `Hello` in the current scope
+//~^ ERROR the trait bound `Hello: IntoDiagnosticArg` is not satisfied
 #[error(code = "E0123", slug = "foo")]
 struct ArgFieldWithoutSkip {
     #[primary_span]
@@ -482,3 +482,25 @@ struct VecField {
     #[label]
     spans: Vec<Span>,
 }
+
+#[derive(SessionDiagnostic)]
+#[error(code = "E0123", slug = "foo")]
+struct UnitField {
+    #[primary_span]
+    spans: Span,
+    #[help]
+    foo: (),
+    #[help = "a"]
+    bar: (),
+}
+
+#[derive(SessionDiagnostic)]
+#[error(code = "E0123", slug = "foo")]
+struct OptUnitField {
+    #[primary_span]
+    spans: Span,
+    #[help]
+    foo: Option<()>,
+    #[help = "a"]
+    bar: Option<()>,
+}
diff --git a/src/test/ui-fulldeps/session-diagnostic/diagnostic-derive.stderr b/src/test/ui-fulldeps/session-diagnostic/diagnostic-derive.stderr
index b1738b60bc0..2583363120a 100644
--- a/src/test/ui-fulldeps/session-diagnostic/diagnostic-derive.stderr
+++ b/src/test/ui-fulldeps/session-diagnostic/diagnostic-derive.stderr
@@ -349,17 +349,26 @@ error: cannot find attribute `nonsense` in this scope
 LL |     #[nonsense]
    |       ^^^^^^^^
 
-error[E0599]: no method named `into_diagnostic_arg` found for struct `Hello` in the current scope
+error[E0277]: the trait bound `Hello: IntoDiagnosticArg` is not satisfied
   --> $DIR/diagnostic-derive.rs:329:10
    |
-LL | struct Hello {}
-   | ------------ method `into_diagnostic_arg` not found for this
-...
 LL | #[derive(SessionDiagnostic)]
-   |          ^^^^^^^^^^^^^^^^^ method not found in `Hello`
-   |
+   |          ^^^^^^^^^^^^^^^^^ the trait `IntoDiagnosticArg` is not implemented for `Hello`
+   |
+   = help: the following other types implement trait `IntoDiagnosticArg`:
+             &'a str
+             Ident
+             String
+             Symbol
+             rustc_middle::ty::Ty<'tcx>
+             usize
+note: required by a bound in `DiagnosticBuilder::<'a, G>::set_arg`
+  --> $COMPILER_DIR/rustc_errors/src/diagnostic_builder.rs:531:19
+   |
+LL |         arg: impl IntoDiagnosticArg,
+   |                   ^^^^^^^^^^^^^^^^^ required by this bound in `DiagnosticBuilder::<'a, G>::set_arg`
    = note: this error originates in the derive macro `SessionDiagnostic` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 43 previous errors
 
-For more information about this error, try `rustc --explain E0599`.
+For more information about this error, try `rustc --explain E0277`.
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