Auto merge of #109638 - NotStirred:suggest/non-derive, r=davidtwco

Add suggestion to remove `derive()` if invoked macro is non-derive

Adds to the existing `expected derive macro, found {}` error message:
```
help: remove the surrounding "derive()":
  --> $DIR/macro-path-prelude-fail-4.rs:1:3
   |
LL | #[derive(inline)]
   |   ^^^^^^^      ^
```

This suggestion will either fix the issue, in the case that the macro was valid, or provide a better error message if not

Not ready for merge yet, as the highlighted span is only valid for trivial formatting. Is there a nice way to get the parent span of the macro path within `smart_resolve_macro_path`?

Closes #109589

compiler/rustc_resolve/src/errors.rs

@@ -481,3 +481,30 @@ pub(crate) struct ToolModuleImported {
 #[derive(Diagnostic)]
 #[diag(resolve_module_only)]
 pub(crate) struct ModuleOnly(#[primary_span] pub(crate) Span);
+
+#[derive(Diagnostic, Default)]
+#[diag(resolve_macro_expected_found)]
+pub(crate) struct MacroExpectedFound<'a> {
+    #[primary_span]
+    pub(crate) span: Span,
+    pub(crate) found: &'a str,
+    pub(crate) expected: &'a str,
+    pub(crate) macro_path: &'a str,
+    #[subdiagnostic]
+    pub(crate) remove_surrounding_derive: Option<RemoveSurroundingDerive>,
+    #[subdiagnostic]
+    pub(crate) add_as_non_derive: Option<AddAsNonDerive<'a>>,
+}
+
+#[derive(Subdiagnostic)]
+#[help(resolve_remove_surrounding_derive)]
+pub(crate) struct RemoveSurroundingDerive {
+    #[primary_span]
+    pub(crate) span: Span,
+}
+
+#[derive(Subdiagnostic)]
+#[help(resolve_add_as_non_derive)]
+pub(crate) struct AddAsNonDerive<'a> {
+    pub(crate) macro_path: &'a str,
+}

compiler/rustc_resolve/src/macros.rs

@@ -1,6 +1,7 @@
 //! A bunch of methods and structures more or less related to resolving macros and
 //! interface provided by `Resolver` to macro expander.
 
+use crate::errors::{AddAsNonDerive, MacroExpectedFound, RemoveSurroundingDerive};
 use crate::Namespace::*;
 use crate::{BuiltinMacroState, Determinacy};
 use crate::{DeriveData, Finalize, ParentScope, ResolutionError, Resolver, ScopeSet};
@@ -543,12 +544,29 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         };
         if let Some((article, expected)) = unexpected_res {
             let path_str = pprust::path_to_string(path);
-            let msg = format!("expected {}, found {} `{}`", expected, res.descr(), path_str);
-            self.tcx
-                .sess
-                .struct_span_err(path.span, &msg)
-                .span_label(path.span, format!("not {} {}", article, expected))
-                .emit();
+
+            let mut err = MacroExpectedFound {
+                span: path.span,
+                expected,
+                found: res.descr(),
+                macro_path: &path_str,
+                ..Default::default() // Subdiagnostics default to None
+            };
+
+            // Suggest moving the macro out of the derive() if the macro isn't Derive
+            if !path.span.from_expansion()
+                && kind == MacroKind::Derive
+                && ext.macro_kind() != MacroKind::Derive
+            {
+                err.remove_surrounding_derive = Some(RemoveSurroundingDerive { span: path.span });
+                err.add_as_non_derive = Some(AddAsNonDerive { macro_path: &path_str });
+            }
+
+            let mut err = self.tcx.sess.create_err(err);
+            err.span_label(path.span, format!("not {} {}", article, expected));
+
+            err.emit();
+
             return Ok((self.dummy_ext(kind), Res::Err));
         }