From c4805ecd3dde4bd9fca24b34b6ad30fcb4c37455 Mon Sep 17 00:00:00 2001
From: James O'Leary <jpohhhh@gmail.com>
Date: Thu, 19 Mar 2026 08:19:27 -0700
Subject: [PATCH 1/2] chat : handle tool calls with no required args in
 TAG_WITH_TAGGED format

---
 common/chat-auto-parser-generator.cpp |  4 +++-
 tests/test-chat.cpp                   | 21 +++++++++++++++++++--
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/common/chat-auto-parser-generator.cpp b/common/chat-auto-parser-generator.cpp
index f19819494c8..d508c73a90d 100644
--- a/common/chat-auto-parser-generator.cpp
+++ b/common/chat-auto-parser-generator.cpp
@@ -384,7 +384,9 @@ common_peg_parser analyze_tools::build_tool_parser_tag_tagged(parser_build_conte
             func_parser = p.atomic(p.tool_open(function.name_prefix + p.tool_name(p.literal(name)) + function.name_suffix) +
                 call_id_section) + p.space() + args_seq;
             matched_atomic = true;
-        } else if (!arguments.name_prefix.empty() && properties.size() > 0) {
+        } else if (!arguments.name_prefix.empty() && !required_parsers.empty()) {
+            // Only peek for an arg tag when there are required args that must follow.
+            // When all args are optional, the model may emit no arg tags at all (#20650).
             func_parser = p.atomic(p.tool_open(function.name_prefix + p.tool_name(p.literal(name)) + function.name_suffix) +
                 call_id_section + p.space() + p.peek(p.literal(arguments.name_prefix))) + args_seq;
             matched_atomic = true;
diff --git a/tests/test-chat.cpp b/tests/test-chat.cpp
index 915b6f71dc5..a39de1d1cbd 100644
--- a/tests/test-chat.cpp
+++ b/tests/test-chat.cpp
@@ -1912,9 +1912,26 @@ static void test_template_output_peg_parsers(bool detailed_debug) {
         })
             .expect_tool_calls({
                 { "special_function", R"({"arg1": 1})", {} },
-                { "special_function_with_opt", R"({"arg1": 1, "arg2": 2})", {} },
-            })
+                { "special_function_with_opt", R"({"arg1": 1, "arg2": 2})", {} },            })
             .run();
+
+        // #20650: tool with no required args, model emits <tool_call>name</tool_call> with no arg tags.
+        {
+            static common_chat_tool no_args_tool{
+                "read_file_diff_md", "Reads a file diff",
+                R"({"type":"object","properties":{"review_id":{"type":"string"},"file_id":{"type":"string"}}})",
+            };
+            tst.test(
+                   "Let me read the diff content."
+                   "</think>"
+                   "<tool_call>read_file_diff_md</tool_call>")
+                .enable_thinking(true)
+                .reasoning_format(COMMON_REASONING_FORMAT_DEEPSEEK)
+                .tools({ no_args_tool })
+                .expect_reasoning("Let me read the diff content.")
+                .expect_tool_calls({{ "read_file_diff_md", "{}", {} }})
+                .run();
+        }
     }
 
     // Kimi-K2-Thinking tests - custom parser

From 12e1dcc6f2c7ac73d31b115bdd1c8147f65424b8 Mon Sep 17 00:00:00 2001
From: "Piotr Wilkin (ilintar)" <piotr.wilkin@syndatis.com>
Date: Thu, 19 Mar 2026 17:52:52 +0100
Subject: [PATCH 2/2] Update tests/test-chat.cpp [no ci]

Co-authored-by: Aldehir Rojas <hello@alde.dev>
---
 tests/test-chat.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tests/test-chat.cpp b/tests/test-chat.cpp
index a39de1d1cbd..d6bfdf45ad7 100644
--- a/tests/test-chat.cpp
+++ b/tests/test-chat.cpp
@@ -1912,7 +1912,8 @@ static void test_template_output_peg_parsers(bool detailed_debug) {
         })
             .expect_tool_calls({
                 { "special_function", R"({"arg1": 1})", {} },
-                { "special_function_with_opt", R"({"arg1": 1, "arg2": 2})", {} },            })
+                { "special_function_with_opt", R"({"arg1": 1, "arg2": 2})", {} },
+            })
             .run();
 
         // #20650: tool with no required args, model emits <tool_call>name</tool_call> with no arg tags.