gccrs: Add ast validation check on union variant number

Unions with zero fields are forbidden. Add regression test for empty
unions.

gcc/rust/ChangeLog:

	* checks/errors/rust-ast-validation.cc (ASTValidation::visit): Add
	zero field check during ast validation pass.
	* checks/errors/rust-ast-validation.h: Add union visit function
	prototype.

gcc/testsuite/ChangeLog:

	* rust/compile/const_generics_8.rs: Fill the union with dummy values.
	* rust/compile/empty_union.rs: New test.

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

2 files changed, 12 insertions, 0 deletions

diff --git a/gcc/rust/checks/errors/rust-ast-validation.cc b/gcc/rust/checks/errors/rust-ast-validation.cc
index 4142cc6..dad7f5e 100644
--- a/gcc/rust/checks/errors/rust-ast-validation.cc
+++ b/gcc/rust/checks/errors/rust-ast-validation.cc
@@ -18,6 +18,7 @@
 
 #include "rust-ast-validation.h"
 #include "rust-diagnostics.h"
+#include "rust-item.h"
 #include "rust-keyword-values.h"
 
 namespace Rust {
@@ -82,6 +83,15 @@ ASTValidation::visit (AST::ExternalFunctionItem &item)
 }
 
 void
+ASTValidation::visit (AST::Union &item)
+{
+  if (item.get_variants ().empty ())
+    rust_error_at (item.get_locus (), "unions cannot have zero fields");
+
+  AST::ContextualASTVisitor::visit (item);
+}
+
+void
 ASTValidation::visit (AST::Function &function)
 {
   std::set<Context> valid_context
diff --git a/gcc/rust/checks/errors/rust-ast-validation.h b/gcc/rust/checks/errors/rust-ast-validation.h
index 49133ee..1052168 100644
--- a/gcc/rust/checks/errors/rust-ast-validation.h
+++ b/gcc/rust/checks/errors/rust-ast-validation.h
@@ -21,6 +21,7 @@
 
 #include "rust-ast-visitor.h"
 #include "rust-ast-full.h"
+#include "rust-item.h"
 
 namespace Rust {
 
@@ -37,6 +38,7 @@ public:
   virtual void visit (AST::Lifetime &lifetime);
   virtual void visit (AST::LoopLabel &label);
   virtual void visit (AST::ExternalFunctionItem &item);
+  virtual void visit (AST::Union &item);
   virtual void visit (AST::Function &function);
   virtual void visit (AST::Trait &trait);
 };