Add feature gate for box syntax

The box syntax is experimental even though it is used in the standard
library. It should be feature gated to prevent anyone from using it in
stable rust.

gcc/rust/ChangeLog:

	* checks/errors/rust-feature-gate.cc (FeatureGate::visit): Allow
	visitor recursion in functions. Also add the gate for the box syntax.
	* checks/errors/rust-feature-gate.h: Remove several recursion fences
	in the feature gate visitor.
	* checks/errors/rust-feature.cc (Feature::create): Add a new feature.
	(Feature::as_name): Likewise.
	* checks/errors/rust-feature.h: Add box_syntax gate.

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

4 files changed, 19 insertions, 4 deletions

diff --git a/gcc/rust/checks/errors/rust-feature-gate.cc b/gcc/rust/checks/errors/rust-feature-gate.cc
index eb23192..33b0387 100644
--- a/gcc/rust/checks/errors/rust-feature-gate.cc
+++ b/gcc/rust/checks/errors/rust-feature-gate.cc
@@ -134,6 +134,8 @@ FeatureGate::visit (AST::Function &function)
 {
   if (!function.is_external ())
     check_rustc_attri (function.get_outer_attrs ());
+
+  AST::DefaultASTVisitor::visit (function);
 }
 
 void
@@ -153,4 +155,13 @@ FeatureGate::visit (AST::TraitImpl &impl)
 	  "negative_impls are not yet implemented");
 };
 
+void
+FeatureGate::visit (AST::BoxExpr &expr)
+{
+  gate (
+    Feature::Name::BOX_SYNTAX, expr.get_locus (),
+    "box expression syntax is experimental; you can call `Box::new` instead");
+  AST::DefaultASTVisitor::visit (expr);
+}
+
 } // namespace Rust
diff --git a/gcc/rust/checks/errors/rust-feature-gate.h b/gcc/rust/checks/errors/rust-feature-gate.h
index d7c84a5..aa90ae2 100644
--- a/gcc/rust/checks/errors/rust-feature-gate.h
+++ b/gcc/rust/checks/errors/rust-feature-gate.h
@@ -81,7 +81,6 @@ public:
   void visit (AST::MethodCallExpr &expr) override {}
   void visit (AST::FieldAccessExpr &expr) override {}
   void visit (AST::ClosureExprInner &expr) override {}
-  void visit (AST::BlockExpr &expr) override {}
   void visit (AST::ClosureExprInnerTyped &expr) override {}
   void visit (AST::ContinueExpr &expr) override {}
   void visit (AST::BreakExpr &expr) override {}
@@ -92,6 +91,7 @@ public:
   void visit (AST::RangeFromToInclExpr &expr) override {}
   void visit (AST::RangeToInclExpr &expr) override {}
   void visit (AST::ReturnExpr &expr) override {}
+  void visit (AST::BoxExpr &expr) override;
   void visit (AST::UnsafeBlockExpr &expr) override {}
   void visit (AST::LoopExpr &expr) override {}
   void visit (AST::WhileLoopExpr &expr) override {}
@@ -166,7 +166,6 @@ public:
   void visit (AST::SlicePattern &pattern) override {}
   void visit (AST::AltPattern &pattern) override {}
   void visit (AST::EmptyStmt &stmt) override {}
-  void visit (AST::LetStmt &stmt) override {}
   void visit (AST::ExprStmt &stmt) override {}
   void visit (AST::TraitBound &bound) override {}
   void visit (AST::ImplTraitType &type) override {}
diff --git a/gcc/rust/checks/errors/rust-feature.cc b/gcc/rust/checks/errors/rust-feature.cc
index 6249758..18cfa33 100644
--- a/gcc/rust/checks/errors/rust-feature.cc
+++ b/gcc/rust/checks/errors/rust-feature.cc
@@ -45,6 +45,9 @@ Feature::create (Feature::Name name)
     case Feature::Name::NEGATIVE_IMPLS:
       return Feature (Feature::Name::NEGATIVE_IMPLS, Feature::State::ACTIVE,
 		      "negative_impls", "1.0.0", 68318, tl::nullopt, "");
+    case Feature::Name::BOX_SYNTAX:
+      return Feature (Feature::Name::BOX_SYNTAX, Feature::State::ACTIVE,
+		      "box_syntax", "1.0.0", 49733, tl::nullopt, "");
     default:
       rust_unreachable ();
     }
@@ -62,6 +65,7 @@ const std::map<std::string, Feature::Name> Feature::name_hash_map = {
   {"extern_types", Feature::Name::EXTERN_TYPES},
   {"lang_items", Feature::Name::LANG_ITEMS},
   {"no_core", Feature::Name::NO_CORE},
+  {"box_syntax", Feature::Name::BOX_SYNTAX},
 }; // namespace Rust
 
 tl::optional<Feature::Name>
@@ -73,4 +77,4 @@ Feature::as_name (const std::string &name)
   return tl::nullopt;
 }
 
-} // namespace Rust
\ No newline at end of file
+} // namespace Rust
diff --git a/gcc/rust/checks/errors/rust-feature.h b/gcc/rust/checks/errors/rust-feature.h
index 306baf2..238bf07 100644
--- a/gcc/rust/checks/errors/rust-feature.h
+++ b/gcc/rust/checks/errors/rust-feature.h
@@ -46,6 +46,7 @@ public:
     EXTERN_TYPES,
     LANG_ITEMS,
     NO_CORE,
+    BOX_SYNTAX,
   };
 
   const std::string &as_string () { return m_name_str; }
@@ -79,4 +80,4 @@ private:
 };
 
 } // namespace Rust
-#endif
\ No newline at end of file
+#endif