Tests pass in reasoning mode. Also e2e tool test passes.

Author: createthis

common/chat.cpp

@@ -1432,6 +1432,22 @@ static void common_chat_parse_deepseek_v3_1_content(common_chat_msg_parser & bui
 static void common_chat_parse_deepseek_v3_1(common_chat_msg_parser & builder) {
     // DeepSeek V3.1 outputs reasoning content between "<think>" and "</think>" tags, followed by regular content
     // First try to parse using the standard reasoning parsing method
+    LOG_DBG("%s: thinking_forced_open: %s\n", __func__, std::to_string(builder.syntax().thinking_forced_open).c_str());
+
+    bool has_reasoning = false;
+    auto header_start_pos = builder.pos();
+    if (auto res = builder.try_find_literal("<think>")) {
+      has_reasoning = true;
+    }
+    if (auto res = builder.try_find_literal("</think>")) {
+      has_reasoning = true;
+    }
+    builder.move_to(header_start_pos);
+    if (!has_reasoning && builder.syntax().thinking_forced_open) {
+        LOG_DBG("%s: edge case no reasoning, adding content\n", __func__);
+        common_chat_parse_deepseek_v3_1_content(builder);
+        return;
+    }
     if (builder.try_parse_reasoning("<think>", "</think>")) {
         // If reasoning was parsed successfully, the remaining content is regular content
         LOG_DBG("%s: parsed reasoning, adding content\n", __func__);

tests/test-chat-parser.cpp

@@ -213,6 +213,7 @@ static void assert_equals(const char* label, const T& expected, const T& actual)
 }
 
 static void test_deepseek_v3_1_tool_calls() {
+    //common_log_set_verbosity_thold(LOG_DEFAULT_DEBUG);
     // variant: happy path for when it works as the model card says it should
     const char* variant = "simple";
     common_chat_syntax syntax = {
@@ -261,6 +262,23 @@ static void test_deepseek_v3_1_tool_calls() {
         assert_equals(variant, std::string(""), m.content);
         assert_equals(variant, std::string("REASONING"), m.reasoning_content);
     }
+
+    // variant: thinking forced open + missing reasoning + no tool calls
+    {
+        common_chat_syntax syntax = {
+            /* .format = */ COMMON_CHAT_FORMAT_DEEPSEEK_V3_1,
+            /* .reasoning_format = */ COMMON_REASONING_FORMAT_DEEPSEEK,
+            /* .reasoning_in_content = */ false,
+            /* .thinking_forced_open = */ true,
+            /* .parse_tool_calls = */ true,
+        };
+        const char* variant = "thinking_forced_open_missing_reasoning_no_tool_calls";
+        const std::string in = "CONTENT";
+        auto m = common_chat_parse(in, false, syntax);
+        assert_equals<std::size_t>(variant, 0, m.tool_calls.size());
+        assert_equals(variant, std::string("CONTENT"), m.content);
+        assert_equals(variant, std::string(""), m.reasoning_content);
+    }
 }
 
 static void test_with_args(const std::string & input, const std::string & expected, bool parse_as_partial = true, bool is_partial = true) {