[gcc r14-8579] gccrs: Add AST validation check for const in trait

[Arthur Cohen]

https://gcc.gnu.org/g:9279483f6e87258e36345c355720860925a75e3e

commit r14-8579-g9279483f6e87258e36345c355720860925a75e3e
Author: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>
Date:   Wed Nov 22 13:08:13 2023 +0100

    gccrs: Add AST validation check for const in trait
    
    Add a new check in AST validation pass that checks that no function
    declaration in traits are declared const.
    
    gcc/rust/ChangeLog:
    
            * checks/errors/rust-ast-validation.cc (ASTValidation::visit): Add
            const check.
            * checks/errors/rust-ast-validation.h: Add visit function prototype.
    
    Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>

Diff:
---
 gcc/rust/checks/errors/rust-ast-validation.cc | 10 ++++++++++
 gcc/rust/checks/errors/rust-ast-validation.h  |  1 +
 2 files changed, 11 insertions(+)

diff --git a/gcc/rust/checks/errors/rust-ast-validation.cc b/gcc/rust/checks/errors/rust-ast-validation.cc
index 54276e8fd599..2743eb0ca299 100644
--- a/gcc/rust/checks/errors/rust-ast-validation.cc
+++ b/gcc/rust/checks/errors/rust-ast-validation.cc
@@ -117,6 +117,16 @@ ASTValidation::visit (AST::Function &function)
   AST::ContextualASTVisitor::visit (function);
 }
 
+void
+ASTValidation::visit (AST::TraitFunctionDecl &decl)
+{
+  const auto &qualifiers = decl.get_qualifiers ();
+
+  if (context.back () == Context::TRAIT && qualifiers.is_const ())
+    rust_error_at (decl.get_identifier ().get_locus (), ErrorCode::E0379,
+		   "functions in traits cannot be declared const");
+}
+
 void
 ASTValidation::visit (AST::Trait &trait)
 {
diff --git a/gcc/rust/checks/errors/rust-ast-validation.h b/gcc/rust/checks/errors/rust-ast-validation.h
index 01d923ceff33..963357f86cd8 100644
--- a/gcc/rust/checks/errors/rust-ast-validation.h
+++ b/gcc/rust/checks/errors/rust-ast-validation.h
@@ -42,6 +42,7 @@ public:
   virtual void visit (AST::Union &item);
   virtual void visit (AST::Function &function);
   virtual void visit (AST::Trait &trait);
+  virtual void visit (AST::TraitFunctionDecl &decl);
 };
 
 } // namespace Rust