if-statement optional braces when single statement

compiler/parser/parser.odin

@@ -1184,6 +1184,27 @@ parse_block :: proc(parser: ^Parser) -> []ast.Stmt_Id {
 	return body[:]
 }
 
+// parse_branch_body parses an `if` then/else body: a braced block (possibly on
+// a following line) or a single brace-less statement (milestone 16). For the
+// then-branch (`validate_condition`), a brace-less body requires the condition
+// to be parenthesized unless it is a function call; the `else` keyword and the
+// unwrap `|...|` already delimit, so those positions skip the check.
+parse_branch_body :: proc(parser: ^Parser, validate_condition: bool, condition: ast.Expr_Id, has_captures: bool) -> []ast.Stmt_Id {
+	skip_newlines(parser)
+	if current(parser).kind == .Left_Brace {
+		return parse_block(parser)
+	}
+	if validate_condition && !has_captures && condition != ast.INVALID_EXPR && int(condition) < len(parser.module.exprs) {
+		expr := parser.module.exprs[condition]
+		if !expr.parenthesized && expr.kind != .Call {
+			source.add(parser.diagnostics, expr.span, "a brace-less 'if' body requires the condition to be parenthesized unless it is a function call")
+		}
+	}
+	single := make([]ast.Stmt_Id, 1, parser.module.allocator)
+	single[0] = parse_statement(parser)
+	return single
+}
+
 parse_if :: proc(parser: ^Parser) -> ast.Stmt_Id {
 	start := advance(parser) // consume 'if'
 	skip_newlines(parser)
@@ -1226,8 +1247,7 @@ parse_if :: proc(parser: ^Parser) -> ast.Stmt_Id {
 			source.add(parser.diagnostics, current(parser).span, "expected '|' to close unwrap captures")
 		}
 	}
-	skip_newlines(parser)
-	then_body := parse_block(parser)
+	then_body := parse_branch_body(parser, true, condition, len(captures) > 0)
 	else_body: []ast.Stmt_Id = nil
 	saved_cursor := parser.cursor
 	skip_newlines(parser)
@@ -1240,7 +1260,7 @@ parse_if :: proc(parser: ^Parser) -> ast.Stmt_Id {
 			single[0] = nested
 			else_body = single
 		} else {
-			else_body = parse_block(parser)
+			else_body = parse_branch_body(parser, false, ast.INVALID_EXPR, false)
 		}
 	} else {
 		parser.cursor = saved_cursor