Require parenthesized assignment expressions in condition of 'if' statements #2716 (#2729)

* Require parenthesized assignment expressions in condition of 'if' statements #2716

* Move analysis to semantic checker and also check while. And update tests and release notes.

---------

Co-authored-by: Christoffer Lerno <christoffer@aegik.com>

lib/std/encoding/json.c3

@@ -249,7 +249,7 @@ fn JsonTokenType? advance(JsonContext* context) @local
 {
 	char c;
 	// Skip whitespace
-	while WS: (c = read_next(context)!)
+	while WS: ((c = read_next(context)!))
 	{
 		switch (c)
 		{
@@ -272,12 +272,12 @@ fn JsonTokenType? advance(JsonContext* context) @local
 				while COMMENT: (true)
 				{
 					// Skip to */
-					while (c = read_next(context)!)
+					while ((c = read_next(context)!))
 					{
 						if (c == '\n') context.line++;
 						if (c != '*') continue;
 						// Skip through all the '*'
-						while (c = read_next(context)!)
+						while ((c = read_next(context)!))
 						{
 							if (c == '\n') context.line++;
 							if (c != '*') break;

releasenotes.md

@@ -15,6 +15,7 @@
 - Reduced memory usage for backtraces on Linux.
 - On win32 utf-8 console output is now enabled by default in compiled programs
 - Add `$$VERSION` and `$$PRERELEASE` compile time constants.
+- Require () around assignment in conditionals. #2716
 
 ### Fixes
 - Regression with npot vector in struct triggering an assert #2219.

src/compiler/sema_stmts.c

@@ -1192,15 +1192,26 @@ static inline bool sema_analyse_cond(SemaContext *context, Expr *expr, CondType
 			{
 				RETURN_SEMA_ERROR(last->decl_expr->var.init_expr, "The expression needs to be convertible to a boolean.");
 			}
+
 			cast_no_check(last, type_bool, false);
 		}
 		if (cast_to_bool && expr_is_const_bool(init))
 		{
 			*result = init->const_expr.b ? COND_TRUE : COND_FALSE;
 		}
-
 		return true;
 	}
+	if (cast_to_bool && last->expr_kind == EXPR_BINARY && last->binary_expr.operator >= BINARYOP_ASSIGN && !last->binary_expr.grouped)
+	{
+		if (vec_size(expr->cond_expr) > 1)
+		{
+			RETURN_SEMA_ERROR(last, "An assignment in the last conditional must be parenthesized - did you mean to use '==' instead?");
+		}
+		else
+		{
+			RETURN_SEMA_ERROR(last, "An assignment in a conditional must have an extra parenthesis - did you mean to use '==' instead?");
+		}
+	}
 
 	// 3a. Check for optional in case of an expression.
 	if (IS_OPTIONAL(last))

test/test_suite/clang/2002-07.c3t

@@ -266,13 +266,13 @@ fn double mathFunc(double x, double y, double z,
 
 
 fn void strcpy(char *s1, char *s2) {
-  while (*s1++ = *s2++);
+  while ((*s1++ = *s2++));
 }
 
 fn void strcat(char *s1, char *s2) {
   while (*s1++);
   s1--;
-  while (*s1++ = *s2++);
+  while ((*s1++ = *s2++));
 }
 
 fn int strcmp(char *s1, char *s2) {

test/test_suite/statements/if_assign.c3

@@ -0,0 +1,12 @@
+fn void main()
+{
+	int x = 5;
+
+	if (x = 1) {}  // #error: An assignment in a conditional must have an extra parenthesis
+
+	if ((x = 1)) {}
+
+	while (x = 1) {} // #error: An assignment in a conditional must have an extra parenthesis
+
+	while (x = 1, x = 1) {} // #error: An assignment in the last conditional must be parenthesized
+}

test/test_suite/statements/while_statement_placement2.c3

@@ -12,7 +12,7 @@ macro @thing(; @body())
 }
 
 fn void strcpy(char *s1, char *s2) {
-  while (*s1++ = *s2++);
+  while ((*s1++ = *s2++));
 }
 
 fn void main()