gccrs: feat: Made changes to ensure no wrong assignments are done.

gcc/rust/ChangeLog:

	* backend/rust-compile-base.cc (HIRCompileBase::lvalue_p): Created a function that
	checks for lvalue.
	* backend/rust-compile-base.h: Created the Signature for above function.
	* backend/rust-compile-expr.cc (CompileExpr::visit): Made changes to ensure
	proper readability and checking for wrong assignments.

gcc/testsuite/ChangeLog:

	* rust/compile/issue-3297.rs: New test.
	* rust/compile/issue-3297-2.rs: New test.

Signed-off-by: Sri Ganesh Thota <[email protected]>

Author: sriganeshres

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

@@ -1015,5 +1015,51 @@ HIRCompileBase::unit_expression (location_t locus)
   return Backend::constructor_expression (unit_type, false, {}, -1, locus);
 }
 
+bool
+HIRCompileBase::is_lvalue (const_tree ref)
+{
+  const enum tree_code code = TREE_CODE (ref);
+
+  switch (code)
+    {
+    case REALPART_EXPR:
+    case IMAGPART_EXPR:
+    case COMPONENT_REF:
+      return is_lvalue (TREE_OPERAND (ref, 0));
+
+    case COMPOUND_LITERAL_EXPR:
+    case STRING_CST:
+    case CONST_DECL:
+    case INTEGER_CST:
+      return true;
+
+    case MEM_REF:
+    case TARGET_MEM_REF:
+      /* MEM_REFs can appear from -fgimple parsing or folding, so allow them
+	 here as well.  */
+    case INDIRECT_REF:
+    case ARRAY_REF:
+    case VAR_DECL:
+    case PARM_DECL:
+    case RESULT_DECL:
+    case ERROR_MARK:
+      return (TREE_CODE (TREE_TYPE (ref)) != FUNCTION_TYPE
+	      && TREE_CODE (TREE_TYPE (ref)) != METHOD_TYPE);
+
+    case BIND_EXPR:
+      return TREE_CODE (TREE_TYPE (ref)) == ARRAY_TYPE;
+    case PLUS_EXPR:
+    case MINUS_EXPR:
+    case MULT_EXPR:
+    case POINTER_PLUS_EXPR:
+    case POINTER_DIFF_EXPR:
+    case MULT_HIGHPART_EXPR:
+    case TRUNC_DIV_EXPR:
+      return false;
+    default:
+      return false;
+    }
+}
+
 } // namespace Compile
 } // namespace Rust

gcc/rust/backend/rust-compile-base.h

@@ -30,6 +30,7 @@ class HIRCompileBase
   virtual ~HIRCompileBase () {}
 
   static tree address_expression (tree expr, location_t locus);
+  bool is_lvalue (const_tree ref);
 
 protected:
   HIRCompileBase (Context *ctx) : ctx (ctx) {}

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

@@ -964,6 +964,17 @@ CompileExpr::visit (HIR::AssignmentExpr &expr)
   auto lvalue = CompileExpr::Compile (expr.get_lhs (), ctx);
   auto rvalue = CompileExpr::Compile (expr.get_rhs (), ctx);
 
+  bool validl_value = is_lvalue (lvalue);
+
+  if (!validl_value
+      || expr.get_lhs ().get_expression_type ()
+	   == HIR::Expr::ExprType::Operator)
+    {
+      rust_error_at (expr.get_lhs ().get_locus (), ErrorCode::E0770,
+		     "invalid left-hand side of assignment");
+      return;
+    }
+
   // assignments are coercion sites so lets convert the rvalue if necessary
   TyTy::BaseType *expected = nullptr;
   TyTy::BaseType *actual = nullptr;

gcc/testsuite/rust/compile/issue-3297-2.rs

@@ -0,0 +1,4 @@
+pub fn main() {
+    let mut x = 42;
+    x += 1;
+}

gcc/testsuite/rust/compile/issue-3297.rs

@@ -0,0 +1,4 @@
+pub fn main() {
+    let mut x = 42;
+    x + 1= 2; // { dg-error "invalid left-hand side of assignment" }
+}