Add note to 'macro not found' to point to identically-named imports.

Author: m-ou-se

compiler/rustc_resolve/src/macros.rs

@@ -19,7 +19,7 @@ use rustc_expand::base::{SyntaxExtension, SyntaxExtensionKind};
 use rustc_expand::compile_declarative_macro;
 use rustc_expand::expand::{AstFragment, Invocation, InvocationKind, SupportsMacroExpansion};
 use rustc_feature::is_builtin_attr_name;
-use rustc_hir::def::{self, DefKind, NonMacroAttrKind};
+use rustc_hir::def::{self, DefKind, Namespace, NonMacroAttrKind};
 use rustc_hir::def_id::{CrateNum, LocalDefId};
 use rustc_hir::PrimTy;
 use rustc_middle::middle::stability;
@@ -1115,6 +1115,24 @@ impl<'a> Resolver<'a> {
                     let msg = format!("cannot find {} `{}` in this scope", expected, ident);
                     let mut err = self.session.struct_span_err(ident.span, &msg);
                     self.unresolved_macro_suggestions(&mut err, kind, &parent_scope, ident);
+                    if let Ok(binding) = self.early_resolve_ident_in_lexical_scope(
+                        ident,
+                        ScopeSet::All(Namespace::TypeNS, false),
+                        &parent_scope,
+                        false,
+                        false,
+                        ident.span,
+                    ) {
+                        if let crate::NameBindingKind::Import { import, .. } = binding.kind {
+                            err.span_note(
+                                import.span,
+                                &format!(
+                                    "`{}` is imported here, but it is not a {}",
+                                    ident, expected
+                                ),
+                            );
+                        }
+                    }
                     err.emit();
                 }
             }