checker: fix autofree crash with option/result method chains (#26694)

* checker: fix autofree crash with option/result method chains

* disable sanitizers tests for now

Author: tankf33der

vlib/v/checker/fn.v

@@ -817,11 +817,15 @@ fn (mut c Checker) call_expr(mut node ast.CallExpr) ast.Type {
 				continue
 			}
 			if arg.expr in [ast.Ident, ast.StringLiteral, ast.SelectorExpr, ast.ComptimeSelector]
-				|| (arg.expr is ast.CallExpr && arg.expr.or_block.kind != .absent) {
+				|| autofree_expr_has_or_block_in_chain(arg.expr) {
 				// Simple expressions like variables, string literals, selector expressions
 				// (`x.field`) can't result in allocations and don't need to be assigned to
 				// temporary vars.
 				// Only expressions like `str + 'b'` need to be freed.
+				// Expressions with result/option propagation in the call chain (e.g.
+				// `get_str()!.to_upper()`) cannot be pre-generated safely by
+				// autofree_call_pregen, because the or_block unwrapping internally calls
+				// go_before_last_stmt() which garbles the output buffer.
 				continue
 			}
 			if arg.expr is ast.CallExpr && arg.expr.name in ['json.encode', 'json.encode_pretty'] {
@@ -4161,3 +4165,19 @@ fn (mut c Checker) check_variadic_arg(arg_expr ast.Expr, typ ast.Type, expected_
 			arg_pos)
 	}
 }
+
+// autofree_expr_has_or_block_in_chain returns true if expr is a CallExpr whose call chain
+// contains an or_block (i.e. result/option propagation via `!` or `?`). Used by autofree to
+// skip tmp-var pre-generation for arguments like `get_str()!.to_upper()`, where the inner
+// call's or_block would interfere with output-buffer positioning in autofree_call_pregen.
+fn autofree_expr_has_or_block_in_chain(expr ast.Expr) bool {
+	if expr is ast.CallExpr {
+		if expr.or_block.kind != .absent {
+			return true
+		}
+		if expr.is_method {
+			return autofree_expr_has_or_block_in_chain(expr.left)
+		}
+	}
+	return false
+}

vlib/v/tests/autofree_result_method_chain_test.v

@@ -0,0 +1,28 @@
+// vtest vflags: -autofree
+// vtest build: !sanitize-address-gcc && !sanitize-address-clang
+
+fn get_str_a() ?string {
+	return 'hello world?'
+}
+
+fn process_a(s string) string {
+	return s.to_upper()
+}
+
+fn get_str_b() !string {
+	return 'hello world!'
+}
+
+fn process_b(s string) string {
+	return s.to_upper()
+}
+
+fn test_autofree_chain_a() {
+	result := process_a(get_str_a()?.to_upper())
+	assert result == 'HELLO WORLD?'
+}
+
+fn test_autofree_chain_b() {
+	result := process_b(get_str_b()!.to_upper())
+	assert result == 'HELLO WORLD!'
+}