Add support for Wildcard pattern binding

Wildcard bindings allow us to bind expression to be unused such as:

  let _ = 123;

They are more commonly used in destructuring of tuples such as:

  let my_tuple = (1,2);
  let (a,_) = my_tuple;

This is the initial basic support for the basic form of let _ = ...; and
it also allows us to ignore parameters within functions as well.

Fixes #557

1 files changed, 10 insertions, 0 deletions

diff --git a/gcc/rust/backend/rust-compile-fnparam.h b/gcc/rust/backend/rust-compile-fnparam.h
index 92a7357..a7bf52a 100644
--- a/gcc/rust/backend/rust-compile-fnparam.h
+++ b/gcc/rust/backend/rust-compile-fnparam.h
@@ -52,6 +52,16 @@ public:
       fndecl, pattern.get_identifier (), decl_type, address_taken, locus);
   }
 
+  void visit (HIR::WildcardPattern &pattern) override
+  {
+    decl_type = ctx->get_backend ()->immutable_type (decl_type);
+
+    bool address_taken = false;
+    compiled_param
+      = ctx->get_backend ()->parameter_variable (fndecl, "_", decl_type,
+						 address_taken, locus);
+  }
+
 private:
   CompileFnParam (Context *ctx, tree fndecl, tree decl_type, Location locus,
 		  const HIR::FunctionParam &param)