common : auto-detect spec type from draft GGUF metadata

common/arg.cpp

@@ -574,6 +574,15 @@ 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() ||

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++) {

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);