gccrs: Implement compilation of IdentifierPattern's subpattern bindings

gcc/rust/ChangeLog:

	* backend/rust-compile-pattern.cc: Add support for IdentifierPattern's
		subpattern under CompilePatternBindings.

Signed-off-by: Yap Zhi Heng <yapzhhg@gmail.com>

Author: Polygonalr

gcc/rust/backend/rust-compile-pattern.cc

@@ -666,6 +666,12 @@ CompilePatternBindings::visit (HIR::ReferencePattern &pattern)
 void
 CompilePatternBindings::visit (HIR::IdentifierPattern &pattern)
 {
+  if (pattern.has_subpattern ())
+    {
+      CompilePatternBindings::Compile (pattern.get_subpattern (),
+				       match_scrutinee_expr, ctx);
+    }
+
   if (!pattern.get_is_ref ())
     {
       ctx->insert_pattern_binding (pattern.get_mappings ().get_hirid (),

gcc/testsuite/rust/compile/match-identifierpattern-enum.rs

@@ -0,0 +1,12 @@
+enum Foo {
+    I(i32),
+}
+
+fn main() {
+    let x = Foo::I(1);
+
+    match x {
+        a @ Foo::I(b) => {},
+        _ => {},
+    };
+}

gcc/testsuite/rust/execute/match-identifierpattern-enum.rs

@@ -0,0 +1,15 @@
+enum Foo {
+    I(i32),
+}
+
+fn main() -> i32 {
+    let x = Foo::I(0);
+    let ret = 1;
+
+    match x {
+        _ @ Foo::I(b) => { ret = b },
+        _ => {},
+    };
+
+    ret
+}