common : auto-detect spec type from draft GGUF metadata (#26814)

* common : auto-detect spec type from draft GGUF metadata

When -md loads a local draft model without --spec-type, the sidecar
inference in common_models_handler_apply only checks HF repo sidecars
and misses local files. The draft model loads into VRAM but speculative
decoding never activates (types stays NONE).

Read general.architecture from the draft GGUF header and map:
  dflash + markov_w1.weight tensor -> draft-dspark
  dflash without markov head        -> draft-dflash

Assisted-by: opencode
* common : address review feedback on spec-type auto-detect PR

- Fix comment spacing to match surrounding style (/* .x = */ not /*.x =*/)
- Add LOG_INF when auto-detection fires so users can see why spec decoding enabled
- Document single-file assumption for split-GGUF edge case

Addresses bot review feedback on #26814.

* common : move spec-type GGUF auto-detect into speculative module

- add common_speculative_types_from_gguf() in speculative.cpp/.h
- use gguf_context_ptr (RAII) from ggml-cpp.h
- reduce comments to a single line per AGENTS.md style

Addresses review feedback on #26814

* common : add doc note and join SPC_INF line in spec-type auto-detect

Assisted-by: opencode

diff --git a/common/arg.cpp b/common/arg.cpp
index 9fe7d66e2426939b0babafb99f17804c2e6c72aa..1f70d0ad452505f9bc60cc1c7c8a87b46b4acb2b 100644 (file)
--- a/common/arg.cpp
+++ b/common/arg.cpp
@@ -561,6 +561,15 @@ void common_models_handler_apply(common_models_handler & handler, common_params
         }
     }
 
+    // infer the speculative type from the draft GGUF metadata when none is requested
+    // note: reads only the first split - sharded drafts need an explicit --spec-type
+    if (spec_types_is_default(params) && !params.speculative.draft.mparams.path.empty()) {
+        const auto types_gguf = common_speculative_types_from_gguf(params.speculative.draft.mparams.path);
+        if (!types_gguf.empty()) {
+            params.speculative.types = types_gguf;
+        }
+    }
+
     // when a sidecar type is requested, the draft repo resolves to its sidecar instead of a full model
     const bool spec_sidecar_found = !plan_spec.mtp.local_path.empty() ||
                                     !plan_spec.dflash.local_path.empty() ||

diff --git a/common/speculative.cpp b/common/speculative.cpp
index 652ed4d3a18d19a45521c86a07102ae5c728dc52..862c4f045cccc2f525c2884015e7dfbd3f1634d3 100644 (file)
--- a/common/speculative.cpp
+++ b/common/speculative.cpp
@@ -2,6 +2,7 @@
 
 #include "common.h"
 #include "ggml.h"
+#include "ggml-cpp.h"
 #include "llama.h"
 #include "log.h"
 #include "ngram-cache.h"
@@ -2227,6 +2228,37 @@ common_speculative_type common_speculative_type_from_name(const std::string & na
     return it->second;
 }
 
+std::vector<common_speculative_type> common_speculative_types_from_gguf(const std::string & path) {
+    struct gguf_init_params gguf_params = {
+        /* .no_alloc = */ true,
+        /* .ctx      = */ nullptr,
+    };
+
+    gguf_context_ptr gguf_ctx(gguf_init_from_file(path.c_str(), gguf_params));
+    if (!gguf_ctx) {
+        return {};
+    }
+
+    const int64_t arch_id = gguf_find_key(gguf_ctx.get(), "general.architecture");
+    if (arch_id < 0 || gguf_get_kv_type(gguf_ctx.get(), arch_id) != GGUF_TYPE_STRING) {
+        return {};
+    }
+
+    const std::string arch = gguf_get_val_str(gguf_ctx.get(), arch_id);
+    if (arch != "dflash") {
+        return {};
+    }
+
+    // the Markov head distinguishes draft-dspark from draft-dflash
+    const auto type = gguf_find_tensor(gguf_ctx.get(), "markov_w1.weight") >= 0
+                    ? COMMON_SPECULATIVE_TYPE_DRAFT_DSPARK
+                    : COMMON_SPECULATIVE_TYPE_DRAFT_DFLASH;
+
+    SPC_INF("auto-detected speculative type '%s' from the draft model metadata\n", common_speculative_type_to_str(type).c_str());
+
+    return { type };
+}
+
 static uint32_t common_get_enabled_speculative_configs(const std::vector<common_speculative_type> & configs) {
     uint32_t result = 0;
     for (size_t i = 0; i < configs.size(); i++) {

diff --git a/common/speculative.h b/common/speculative.h
index 06b0992ed681b291b11e0b6f4f100f3ed11cd5af..12ae31b7de59f0f4b60d878749532357048410d9 100644 (file)
--- a/common/speculative.h
+++ b/common/speculative.h
@@ -14,6 +14,9 @@ const char * common_speculative_all_types_str();
 // parse user provided types
 std::vector<enum common_speculative_type> common_speculative_types_from_names(const std::vector<std::string> & names);
 
+// infer the spec types from the GGUF metadata of a draft model; empty if unknown
+std::vector<enum common_speculative_type> common_speculative_types_from_gguf(const std::string & path);
+
 // convert string to type
 enum common_speculative_type common_speculative_type_from_name(const std::string & name);