[gcc r14-7643] gccrs: Allow parsing a borrow from struct expression

[Arthur Cohen]

https://gcc.gnu.org/g:b436709f4b1b0d75fa0b5f1c6c6b22f397a767c9

commit r14-7643-gb436709f4b1b0d75fa0b5f1c6c6b22f397a767c9
Author: Owen Avery <powerboat9.gamer@gmail.com>
Date:   Mon Jun 5 16:48:55 2023 -0400

    gccrs: Allow parsing a borrow from struct expression
    
    gcc/rust/ChangeLog:
    
            * parse/rust-parse-impl.h
            (Parser::null_denotation): Allow struct expression referencing.
    
    gcc/testsuite/ChangeLog:
    
            * rust/compile/struct-expr-parse.rs: New test.
    
    Signed-off-by: Owen Avery <powerboat9.gamer@gmail.com>

Diff:
---
 gcc/rust/parse/rust-parse-impl.h                | 5 ++---
 gcc/testsuite/rust/compile/struct-expr-parse.rs | 7 +++++++
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/gcc/rust/parse/rust-parse-impl.h b/gcc/rust/parse/rust-parse-impl.h
index 9faa374915c..80ffbcc22f9 100644
--- a/gcc/rust/parse/rust-parse-impl.h
+++ b/gcc/rust/parse/rust-parse-impl.h
@@ -12633,11 +12633,10 @@ Parser<ManagedTokenSource>::null_denotation (const_TokenPtr tok,
 	std::unique_ptr<AST::Expr> expr = nullptr;
 	bool is_mut_borrow = false;
 
-	/* HACK: as struct expressions should always be value expressions,
-	 * cannot be referenced */
 	ParseRestrictions entered_from_unary;
 	entered_from_unary.entered_from_unary = true;
-	entered_from_unary.can_be_struct_expr = false;
+	if (!restrictions.can_be_struct_expr)
+	  entered_from_unary.can_be_struct_expr = false;
 
 	if (lexer.peek_token ()->get_id () == MUT)
 	  {
diff --git a/gcc/testsuite/rust/compile/struct-expr-parse.rs b/gcc/testsuite/rust/compile/struct-expr-parse.rs
new file mode 100644
index 00000000000..3c383a90ca4
--- /dev/null
+++ b/gcc/testsuite/rust/compile/struct-expr-parse.rs
@@ -0,0 +1,7 @@
+struct A { // { dg-warning "struct is never constructed" }
+    a: u32
+}
+
+pub fn foo(a: u32) {
+    (&A { a }.a, 1);
+}