From fe2e0575ca48e3a78ada13a1847add5d404daf32 Mon Sep 17 00:00:00 2001
From: Andrei Rusu de Castro <arc@empyreal.works>
Date: Wed, 9 Sep 2026 21:38:52 +0200
Subject: [PATCH] chat : enforce string enums in Qwen XML tool arguments

Use allowed XML literals instead of the unrestricted string production. Require the parameter-close boundary when matching alternatives with shared prefixes. Cover rejected values, empty and escaped strings, parsing, streaming and ordinary-string behavior in the existing chat suite.

Assisted-by: GPT-6 Astra
---
 common/chat.cpp     | 10 ++++++++++
 tests/test-chat.cpp | 44 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 54 insertions(+)

diff --git a/common/chat.cpp b/common/chat.cpp
index 743ecde0a77e..ce3e1cb22fd8 100644
--- a/common/chat.cpp
+++ b/common/chat.cpp
@@ -1270,6 +1270,16 @@ static common_chat_params common_chat_params_init_qwen3_coder(const common_chat_
                     auto arg_value = schema_info.resolves_to_string(param_schema) ?
                         arg_string :
                         p.tool_arg_json_value(p.schema(p.json(), rule_name + "-schema", param_schema)) + arg_close;
+                    if (param_schema.contains("enum") && param_schema.at("enum").is_array() &&
+                        !param_schema.at("enum").empty() &&
+                        std::all_of(param_schema.at("enum").begin(), param_schema.at("enum").end(),
+                                    [](const json & value) { return value.is_string(); })) {
+                        auto values = p.choice();
+                        for (const auto & value : param_schema.at("enum")) {
+                            values |= p.literal(value.get<std::string>()) + p.peek(p.literal("\n</parameter>\n"));
+                        }
+                        arg_value = p.tool_arg_string_value(values) + arg_close;
+                    }
 
                     auto arg_rule = p.rule(rule_name, p.tool_arg(arg_open + arg_value));
 
diff --git a/tests/test-chat.cpp b/tests/test-chat.cpp
index 7918f0ffcf48..41d2c005e5cf 100644
--- a/tests/test-chat.cpp
+++ b/tests/test-chat.cpp
@@ -7154,6 +7154,49 @@ static void test_msg_diffs_compute() {
     }
 }
 
+static void test_qwen_string_enums() {
+    const auto xml = [](const std::string & value) {
+        return "<tool_call>\n<function=records>\n<parameter=action>\n" + value +
+               "\n</parameter>\n</function>\n</tool_call>";
+    };
+    for (const std::string path : {"models/templates/Qwen3-Coder.jinja", "models/templates/Qwen3.5-4B.jinja"}) {
+        auto tmpls = read_templates(path);
+        common_chat_templates_inputs in;
+        in.messages = {message_user};
+        in.reasoning_format = COMMON_REASONING_FORMAT_DEEPSEEK;
+        in.parallel_tool_calls = true;
+        auto schema = json::parse(R"({"type":"object","properties":{"action":{"type":"string","enum":["load","reload","re","","quoted\"value","line\nbreak"]}},"required":["action"],"additionalProperties":false})");
+        in.tools = {{"records", "Access records.", schema.dump()}};
+        auto params = common_chat_templates_apply(tmpls.get(), in);
+        for (const std::string value : {"erase", "loading", "reloaded", " load", "load "}) {
+            auto grammar = build_grammar(params.grammar);
+            assert_equals(true, grammar != nullptr);
+            assert_equals(false, match_string(xml(value), grammar.get()));
+        }
+        for (const auto & value : schema["properties"]["action"]["enum"]) {
+            const auto text = value.get<std::string>();
+            auto grammar = build_grammar(params.grammar);
+            assert_equals(true, match_string(xml(text), grammar.get()));
+            test_peg_parser(tmpls.get(), [&](peg_test_case & tc) {
+                tc.params = in;
+                tc.input = (path.find("Qwen3-Coder") == std::string::npos ? "</think>\n\n" : "") + xml(text);
+                tc.expect = simple_assist_msg("", "", "records", json({{"action", text}}).dump());
+            }, false);
+        }
+        test_peg_parser(tmpls.get(), [&](peg_test_case & tc) {
+            tc.params = in;
+            tc.input = (path.find("Qwen3-Coder") == std::string::npos ? "</think>\n\n" : "") + xml("re") + "\n" + xml("reload");
+            tc.expect.role = "assistant";
+            tc.expect.tool_calls = {{"records", R"({"action":"re"})", ""}, {"records", R"({"action":"reload"})", ""}};
+        }, false);
+        schema["properties"]["action"].erase("enum");
+        in.tools = {{"records", "Access records.", schema.dump()}};
+        params = common_chat_templates_apply(tmpls.get(), in);
+        auto grammar = build_grammar(params.grammar);
+        assert_equals(true, match_string(xml("erase"), grammar.get()));
+    }
+}
+
 int main(int argc, char ** argv) {
     bool detailed_debug    = false;
     bool only_run_filtered = false;
@@ -7226,6 +7269,7 @@ int main(int argc, char ** argv) {
     } else
 #endif
     {
+        test_qwen_string_enums();
         test_msg_diffs_compute();
         test_msgs_oaicompat_json_conversion();
         test_msg_token_delimiters_split();