Avoid suggesting to add unsafe when the extern block is already unsafe

Author: spastorino

compiler/rustc_ast_passes/messages.ftl

@@ -71,6 +71,8 @@ ast_passes_extern_fn_qualifiers = functions in `extern` blocks cannot have quali
     .suggestion = remove this qualifier
 
 ast_passes_extern_invalid_safety = items in unadorned `extern` blocks cannot have safety qualifiers
+
+ast_passes_extern_invalid_safety_with_suggestion = items in unadorned `extern` blocks cannot have safety qualifiers
     .suggestion = add unsafe to this `extern` block
 
 ast_passes_extern_item_ascii = items in `extern` blocks cannot use non-ascii identifiers

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -459,13 +459,15 @@ impl<'a> AstValidator<'a> {
     fn check_item_safety(&self, span: Span, safety: Safety) {
         match self.extern_mod_safety {
             Some(extern_safety) => {
-                if matches!(safety, Safety::Unsafe(_) | Safety::Safe(_))
-                    && (extern_safety == Safety::Default || !self.features.unsafe_extern_blocks)
-                {
-                    self.dcx().emit_err(errors::InvalidSafetyOnExtern {
-                        item_span: span,
-                        block: self.current_extern_span().shrink_to_lo(),
-                    });
+                if matches!(safety, Safety::Unsafe(_) | Safety::Safe(_)) {
+                    if extern_safety == Safety::Default {
+                        self.dcx().emit_err(errors::InvalidSafetyOnExternWithSuggestion {
+                            item_span: span,
+                            block: self.current_extern_span().shrink_to_lo(),
+                        });
+                    } else if !self.features.unsafe_extern_blocks {
+                        self.dcx().emit_err(errors::InvalidSafetyOnExtern { item_span: span });
+                    }
                 }
             }
             None => {

compiler/rustc_ast_passes/src/errors.rs

@@ -221,6 +221,13 @@ pub enum ExternBlockSuggestion {
 pub struct InvalidSafetyOnExtern {
     #[primary_span]
     pub item_span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(ast_passes_extern_invalid_safety_with_suggestion)]
+pub struct InvalidSafetyOnExternWithSuggestion {
+    #[primary_span]
+    pub item_span: Span,
     #[suggestion(code = "unsafe ", applicability = "machine-applicable", style = "verbose")]
     pub block: Span,
 }

tests/ui/parser/unsafe-foreign-mod-2.stderr

@@ -19,11 +19,6 @@ error: items in unadorned `extern` blocks cannot have safety qualifiers
    |
 LL |     unsafe fn foo();
    |     ^^^^^^^^^^^^^^^^
-   |
-help: add unsafe to this `extern` block
-   |
-LL | unsafe extern "C" unsafe {
-   | ++++++
 
 error: aborting due to 3 previous errors