From 6287e8dfbfa1a186236a81ce1ba7bfa05390d193 Mon Sep 17 00:00:00 2001
From: Christoffer Lerno <christoffer@aegik.com>
Date: Fri, 26 Sep 2025 21:19:38 +0200
Subject: [PATCH] Restore some `out` checking.

---
 lib/std/crypto/aes.c3                      |  2 +-
 src/compiler/sema_expr.c                   | 28 ++++++++++++++++++----
 test/test_suite/contracts/out_subscript.c3 |  8 ++++---
 3 files changed, 29 insertions(+), 9 deletions(-)

diff --git a/lib/std/crypto/aes.c3 b/lib/std/crypto/aes.c3
index eb65d60ca..b42a8a13d 100644
--- a/lib/std/crypto/aes.c3
+++ b/lib/std/crypto/aes.c3
@@ -584,7 +584,7 @@ fn void inv_cipher(Aes* aes, char[] round_key)
 
 <*¨
  @param type : "The AES variant to expant the key for"
- @param [out] round_key : "Key to expand into"
+ @param [inout] round_key : "Key to expand into"
  @param [in] key : "The key to expand"
  @require key.len == type.key.key_len : "Key does not match expected length."
 *>
diff --git a/src/compiler/sema_expr.c b/src/compiler/sema_expr.c
index 1acea7107..16a9424ba 100644
--- a/src/compiler/sema_expr.c
+++ b/src/compiler/sema_expr.c
@@ -6676,6 +6676,17 @@ static bool sema_expr_analyse_slice_assign(SemaContext *context, Expr *expr, Typ
 	return true;
 
 SLICE_COPY:;
+	while (right->expr_kind == EXPR_SLICE)
+	{
+		Expr *inner = exprptr(right->slice_expr.expr);
+		if (inner->expr_kind != EXPR_IDENTIFIER) break;
+		Decl *decl = inner->ident_expr;
+		if (decl->decl_kind != DECL_VAR) break;
+		if (!decl->var.out_param || decl->var.in_param) break;
+		if (context->active_scope.flags & (SCOPE_ENSURE | SCOPE_ENSURE_MACRO)) break;
+		RETURN_SEMA_ERROR(right, "'out' parameters may not be read.");
+	}
+
 	if (!sema_analyse_expr_rhs(context, left_type, right, false, NULL, false)) return false;
 	Range *left_range = &left->slice_expr.range;
 	IndexDiff left_len = range_const_len(left_range);
@@ -11661,19 +11672,26 @@ static inline bool sema_cast_rvalue(SemaContext *context, Expr *expr, bool mutat
 		case EXPR_IDENTIFIER:
 			if (mutate && !sema_cast_ident_rvalue(context, expr)) return false;
 			break;
-		case EXPR_SUBSCRIPT:
 		case EXPR_SLICE:
-			/*
 		{
-			Expr *inner = exprptr(expr->expr_kind == EXPR_SUBSCRIPT ? expr->subscript_expr.expr : expr->slice_expr.expr);
+			Expr *inner = exprptr(expr->subscript_expr.expr);
+			if (inner->expr_kind != EXPR_IDENTIFIER) break;
+			Decl *decl = inner->ident_expr;
+			if (decl->decl_kind != DECL_VAR) break;
+			if (!decl->var.out_param || decl->var.in_param) break;
+			if (context->active_scope.flags & (SCOPE_ENSURE | SCOPE_ENSURE_MACRO)) break;
+			break;
+		}
+		case EXPR_SUBSCRIPT:
+		{
+			Expr *inner = exprptr(expr->subscript_expr.expr);
 			if (inner->expr_kind != EXPR_IDENTIFIER) break;
 			Decl *decl = inner->ident_expr;
 			if (decl->decl_kind != DECL_VAR) break;
 			if (!decl->var.out_param || decl->var.in_param) break;
 			if (context->active_scope.flags & (SCOPE_ENSURE | SCOPE_ENSURE_MACRO)) break;
 			RETURN_SEMA_ERROR(expr, "'out' parameters may not be read.");
-		}*/
-			break;
+		}
 		case EXPR_UNARY:
 		{
 			if (expr->unary_expr.operator != UNARYOP_DEREF) break;
diff --git a/test/test_suite/contracts/out_subscript.c3 b/test/test_suite/contracts/out_subscript.c3
index 70a163894..5fca32125 100644
--- a/test/test_suite/contracts/out_subscript.c3
+++ b/test/test_suite/contracts/out_subscript.c3
@@ -5,9 +5,11 @@
  *>
 fn void tes2t(char* z, char[] out_data, char[] in_data) {
 	z[0] = 2;
-	z[0] += 1; // error: 'out' parameters may not be read
+	z[0] += 1; // #error: 'out' parameters may not be read
 	out_data[0] = 3;
-	out_data[0] *= 1;  // error: 'out' parameters may not be read
-	out_data[0..3]; // error: 'out' parameters may not be read
+	out_data[0] *= 1;  // #error: 'out' parameters may not be read
+	out_data[0..3];
 	out_data[0..3] = 23;
+	out_data[0..3] = out_data[0..3]; // #error: parameters may not be read
+
 }
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