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chat : fix LFM2 tool-call parsing double-escaping #24667

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Merged
pwilkin merged 2 commits into from
Jun 15, 2026
Merged

chat : fix LFM2 tool-call parsing double-escaping #24667

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1144451
Add escape test cases
tdakhran Jun 11, 2026
f72edd7
chat : fix LFM2 tool-call parsing double-escaping
tdakhran Jun 15, 2026
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9 changes: 5 additions & 4 deletions common/chat-peg-parser.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -540,10 +540,11 @@ common_peg_parser common_chat_peg_builder::python_style_tool_calls(
auto arg_name_parser = literal(prop_name);

common_peg_parser arg_value_parser = eps();
auto string_value_parser = choice({
literal("\"") + tool_arg_string_value(string_content('"')) + literal("\""),
literal("'") + tool_arg_string_value(string_content('\'')) + literal("'")
});
// Quoted literal as a value: normalize_quotes_to_json preserves escapes.
auto string_value_parser = tool_arg_value(choice({
literal("\"") + string_content('"') + literal("\""),
literal("'") + string_content('\'') + literal("'")
}));

if (is_string_type) {
arg_value_parser = string_value_parser;
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22 changes: 20 additions & 2 deletions tests/test-chat.cpp
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Expand Up @@ -1882,11 +1882,29 @@ static void test_lfm2_parser(const std::string & template_path, bool detailed_de
.expect(simple_assist_msg("Use this format: [link text](url). Example: [Wikipedia](https://www.wikipedia.org)."))
.run();

// Python tool with multiline code in string
// Python tool with multiline code in string: the \n in the literal decodes to a real
// newline, emitted as a JSON \n escape (not a doubled backslash).
tst.test("<|tool_call_start|>[python(code=\"def hello():\\n print('hey')\")]<|tool_call_end|>")
.tools({ python_tool })
.expect_tool_calls({
{ "python", R"#({"code": "def hello():\\n print('hey')"})#", "" }
{ "python", R"#({"code": "def hello():\n print('hey')"})#", "" }
})
.run();

// String escape sequences decode to their actual characters (newline + tab here),
// so a "write a two line file" style call produces real line breaks, not literal "\n".
tst.test("<|tool_call_start|>[python(code=\"First line\\nSecond line\\tindented\")]<|tool_call_end|>")
.tools({ python_tool })
.expect_tool_calls({
{ "python", R"#({"code": "First line\nSecond line\tindented"})#", "" }
})
.run();

// Escaped quotes inside a string argument survive the round-trip.
tst.test("<|tool_call_start|>[python(code=\"print(\\\"hi\\\")\")]<|tool_call_end|>")
.tools({ python_tool })
.expect_tool_calls({
{ "python", R"#({"code": "print(\"hi\")"})#", "" }
})
.run();

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