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common : enable reasoning budget sampler for gemma4 (#21697)

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* fix: enable reasoning budget sampler for gemma4

Add thinking_start_tag and thinking_end_tag to
common_chat_params_init_gemma4(). Without these, the reasoning
budget sampler never activates for gemma4.

Make the newline after "thought" optional in the PEG parser to
handle budget=0 (sampler forces end tag before the newline).

Add test case for empty thinking block.

Fixes #21487

* use p.space() instead of p.optional(p.literal("\n")) in gemma4 thought parser
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Berk Idem
2026-04-10 05:49:14 -04:00
committed by GitHub
parent 3f8752b559
commit d7ff074c87
2 changed files with 12 additions and 3 deletions
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common/chat.cpp
+5 -3
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@@ -1083,7 +1083,9 @@ static common_chat_params common_chat_params_init_gemma4(const common_chat_templ
data.prompt = common_chat_template_direct_apply_impl(tmpl, inputs);
data.format = COMMON_CHAT_FORMAT_PEG_GEMMA4;
data.supports_thinking = true;
data.supports_thinking = true;
data.thinking_start_tag = "<|channel>thought";
data.thinking_end_tag = "<channel|>";
data.preserved_tokens = {
"<|channel>",
@@ -1102,9 +1104,9 @@ static common_chat_params common_chat_params_init_gemma4(const common_chat_templ
auto start = p.rule("start", p.prefix(inputs.generation_prompt, "<|channel>"));
if (extract_reasoning) {
p.rule("thought", p.literal("<|channel>thought\n") + p.reasoning(p.until("<channel|>")) + p.literal("<channel|>"));
p.rule("thought", p.literal("<|channel>thought") + p.space() + p.reasoning(p.until("<channel|>")) + p.literal("<channel|>"));
} else {
p.rule("thought", p.content(p.literal("<|channel>thought\n") + p.until("<channel|>") + p.literal("<channel|>")));
p.rule("thought", p.content(p.literal("<|channel>thought") + p.space() + p.until("<channel|>") + p.literal("<channel|>")));
}
auto thought = (p.peek(p.literal("<|channel>")) + p.ref("thought")) | p.negate(p.literal("<|channel>"));