Emit an error on unsafe modules

An error should be emitted on unsafe modules during the AST validation
pass as the syntax allows those even though they're not alowed later down
the line.

gcc/rust/ChangeLog:

	* ast/rust-item.h: Add safety getter to modules.
	* checks/errors/rust-ast-validation.cc (ASTValidation::visit): Check
	a module's safety and emit an error when meeting an unsafe module.
	* checks/errors/rust-ast-validation.h: Add function prototype.
	* parse/rust-parse-impl.h (Parser::parse_module): Move the module locus
	to the first token instead of the mod keyword.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>

gcc/rust/ast/rust-item.h

@@ -840,6 +840,8 @@ class Module : public VisItem
   // Returns the kind of the module
   enum ModuleKind get_kind () const { return kind; }
 
+  Unsafety get_unsafety () const { return safety; }
+
   // TODO: think of better way to do this - mutable getter seems dodgy
   const std::vector<Attribute> &get_inner_attrs () const { return inner_attrs; }
   std::vector<Attribute> &get_inner_attrs () { return inner_attrs; }

gcc/rust/checks/errors/rust-ast-validation.cc

@@ -17,6 +17,7 @@
 // <http://www.gnu.org/licenses/>.
 
 #include "rust-ast-validation.h"
+#include "rust-common.h"
 #include "rust-diagnostics.h"
 #include "rust-item.h"
 #include "rust-keyword-values.h"
@@ -136,4 +137,13 @@ ASTValidation::visit (AST::Trait &trait)
   AST::ContextualASTVisitor::visit (trait);
 }
 
+void
+ASTValidation::visit (AST::Module &module)
+{
+  if (module.get_unsafety () == Unsafety::Unsafe)
+    rust_error_at (module.get_locus (), "module cannot be declared unsafe");
+
+  AST::ContextualASTVisitor::visit (module);
+}
+
 } // namespace Rust

gcc/rust/checks/errors/rust-ast-validation.h

@@ -34,6 +34,7 @@ class ASTValidation : public AST::ContextualASTVisitor
 
   void check (AST::Crate &crate) { AST::ContextualASTVisitor::visit (crate); }
 
+  virtual void visit (AST::Module &module);
   virtual void visit (AST::ConstantItem &const_item);
   virtual void visit (AST::Lifetime &lifetime);
   virtual void visit (AST::LoopLabel &label);

gcc/rust/parse/rust-parse-impl.h

@@ -2429,14 +2429,15 @@ std::unique_ptr<AST::Module>
 Parser<ManagedTokenSource>::parse_module (AST::Visibility vis,
 					  AST::AttrVec outer_attrs)
 {
+  location_t locus = lexer.peek_token ()->get_locus ();
+
   Unsafety safety = Unsafety::Normal;
   if (lexer.peek_token ()->get_id () == UNSAFE)
     {
       safety = Unsafety::Unsafe;
       skip_token (UNSAFE);
     }
 
-  location_t locus = lexer.peek_token ()->get_locus ();
   skip_token (MOD);
 
   const_TokenPtr module_name = expect_token (IDENTIFIER);