prevents closure parameters from being declared as refrences (#7078)

crates/cairo-lang-semantic/src/diagnostic.rs

@@ -997,6 +997,9 @@ impl DiagnosticEntry for SemanticDiagnostic {
             SemanticDiagnosticKind::RefClosureArgument => {
                 "Arguments to closure functions cannot be references".into()
             }
+            SemanticDiagnosticKind::RefClosureParam => {
+                "Closure parameters cannot be references".into()
+            }
             SemanticDiagnosticKind::MutableCapturedVariable => {
                 "Capture of mutable variables in a closure is not supported".into()
             }
@@ -1422,6 +1425,7 @@ pub enum SemanticDiagnosticKind {
         shadowed_function_name: SmolStr,
     },
     RefClosureArgument,
+    RefClosureParam,
     MutableCapturedVariable,
     NonTraitTypeConstrained {
         identifier: SmolStr,

crates/cairo-lang-semantic/src/expr/compute.rs

@@ -1664,6 +1664,10 @@ fn compute_expr_closure_semantic(
             vec![]
         };
 
+        params.iter().filter(|param| param.mutability == Mutability::Reference).for_each(|param| {
+            new_ctx.diagnostics.report(param.stable_ptr(ctx.db.upcast()), RefClosureParam);
+        });
+
         new_ctx
             .semantic_defs
             .extend(new_ctx.environment.variables.iter().map(|(_, var)| (var.id(), var.clone())));

crates/cairo-lang-semantic/src/expr/test_data/closure

@@ -743,3 +743,28 @@ error: Cannot assign to an immutable variable.
  --> lib.cairo:3:9
         a = a + 2
         ^^^^^^^^^
+
+//! > ==========================================================================
+
+//! > Closures with ref arguments.
+
+//! > test_runner_name
+test_function_diagnostics(expect_diagnostics: true)
+
+//! > function
+fn foo() {
+    let _ = |ref a| {
+        a = a + 2
+    };
+}
+
+//! > function_name
+foo
+
+//! > module_code
+
+//! > expected_diagnostics
+error: Closure parameters cannot be references
+ --> lib.cairo:2:14
+    let _ = |ref a| {
+             ^^^^^