Update AttrInput with AttrInputType

This allows us to switch based on the type which can be used for more complex usage of attributes such as lang_item parsing.

Addresses #742

Author: philberty

gcc/rust/ast/rust-ast.h

@@ -542,6 +542,13 @@ struct Attribute
 class AttrInput
 {
 public:
+  enum AttrInputType
+  {
+    LITERAL,
+    META_ITEM,
+    TOKEN_TREE,
+  };
+
   virtual ~AttrInput () {}
 
   // Unique pointer custom clone function
@@ -564,6 +571,8 @@ class AttrInput
   // Returns whether attr input has been parsed to meta item syntax.
   virtual bool is_meta_item () const = 0;
 
+  virtual AttrInputType get_attr_input_type () const = 0;
+
 protected:
   // pure virtual clone implementation
   virtual AttrInput *clone_attr_input_impl () const = 0;
@@ -650,6 +659,11 @@ class AttrInputMetaItemContainer : public AttrInput
 
   bool check_cfg_predicate (const Session &session) const override;
 
+  AttrInputType get_attr_input_type () const final override
+  {
+    return AttrInput::AttrInputType::META_ITEM;
+  }
+
   // Clones this object.
   std::unique_ptr<AttrInputMetaItemContainer>
   clone_attr_input_meta_item_container () const
@@ -767,6 +781,11 @@ class DelimTokenTree : public TokenTree, public AttrInput
   }
 
   bool is_meta_item () const override { return false; }
+
+  AttrInputType get_attr_input_type () const final override
+  {
+    return AttrInput::AttrInputType::TOKEN_TREE;
+  }
 };
 
 /* Forward decl - definition moved to rust-expr.h as it requires LiteralExpr to

gcc/rust/ast/rust-expr.h

@@ -102,13 +102,7 @@ class LiteralExpr : public ExprWithoutBlock
 // Literal expression attribute body (non-macro attribute)
 class AttrInputLiteral : public AttrInput
 {
-  // Literal expression WITHOUT SUFFIX
-  // std::unique_ptr<LiteralExpr> literal_expr;
-  LiteralExpr
-    literal_expr; // as not using polymorphic behaviour, doesn't require pointer
-  // TODO: will require pointer if LiteralExpr is changed to have subclassing
-
-  // TODO: should this store location data?
+  LiteralExpr literal_expr;
 
 public:
   AttrInputLiteral (LiteralExpr lit_expr) : literal_expr (std::move (lit_expr))
@@ -127,6 +121,13 @@ class AttrInputLiteral : public AttrInput
 
   bool is_meta_item () const override { return false; }
 
+  LiteralExpr &get_literal () { return literal_expr; }
+
+  AttrInputType get_attr_input_type () const final override
+  {
+    return AttrInput::AttrInputType::LITERAL;
+  }
+
 protected:
   /* Use covariance to implement clone function as returning this object rather
    * than base */