Update the deadcode pass to scan into modules and respect underscores on type names

Author: philberty

gcc/rust/lint/rust-lint-marklive.h

@@ -262,6 +262,12 @@ class MarkLive : public MarkLiveBase
     stct.get_struct_base ()->base_struct->accept_vis (*this);
   }
 
+  void visit (HIR::Module &module) override
+  {
+    for (auto &item : module.get_items ())
+      item->accept_vis (*this);
+  }
+
 private:
   std::vector<HirId> worklist;
   std::set<HirId> liveSymbols;

gcc/rust/lint/rust-lint-scan-deadcode.h

@@ -81,9 +81,11 @@ class ScanDeadcode : public MarkLiveBase
     HirId hirId = stct.get_mappings ().get_hirid ();
     if (should_warn (hirId))
       {
-	rust_warning_at (stct.get_locus (), 0,
-			 "struct is never constructed: %<%s%>",
-			 stct.get_identifier ().c_str ());
+	bool name_starts_underscore = stct.get_identifier ().at (0) == '_';
+	if (!name_starts_underscore)
+	  rust_warning_at (stct.get_locus (), 0,
+			   "struct is never constructed: %<%s%>",
+			   stct.get_identifier ().c_str ());
       }
     else
       {
@@ -124,6 +126,12 @@ class ScanDeadcode : public MarkLiveBase
       }
   }
 
+  void visit (HIR::Module &mod) override
+  {
+    for (auto &item : mod.get_items ())
+      item->accept_vis (*this);
+  }
+
 private:
   std::set<HirId> live_symbols;
   Resolver::Resolver *resolver;

gcc/testsuite/rust/compile/torture/mod-nameresolve.rs

@@ -1,5 +1,6 @@
-mod foo { // { dg-warning "unused name" }
-    struct A; // { dg-warning "unused name" }
+// { dg-additional-options "-w" }
+mod foo {
+    struct A;
 }
 
 fn main() {}