imatrix : warn when GGUF imatrix is saved without .gguf suffix (ggml-org#15076)

* imatrix : add warning when suffix is not .gguf for GGUF imatrix

* imatrix : only warn about suffix when output format is unspecified

Author: compilade

common/arg.cpp

@@ -2648,10 +2648,10 @@ common_params_context common_params_parser_init(common_params & params, llama_ex
     ).set_examples({LLAMA_EXAMPLE_IMATRIX}));
     add_opt(common_arg(
         {"--output-format"}, "{gguf,dat}",
-        string_format("output format for imatrix file (default: %s)", params.imat_dat ? "dat" : "gguf"),
+        string_format("output format for imatrix file (default: %s)", params.imat_dat > 0 ? "dat" : "gguf"),
         [](common_params & params, const std::string & value) {
-            /**/ if (value == "gguf") { params.imat_dat = false; }
-            else if (value == "dat")  { params.imat_dat = true;  }
+            /**/ if (value == "gguf") { params.imat_dat = -1; }
+            else if (value == "dat")  { params.imat_dat = 1;  }
             else { throw std::invalid_argument("invalid output format"); }
         }
     ).set_examples({LLAMA_EXAMPLE_IMATRIX}));

common/common.h

@@ -434,7 +434,7 @@ struct common_params {
     int32_t n_out_freq  = 10; // output the imatrix every n_out_freq iterations
     int32_t n_save_freq =  0; // save the imatrix every n_save_freq iterations
     int32_t i_chunk     =  0; // start processing from this chunk
-    bool    imat_dat    = false; // whether the legacy imatrix.dat format should be output
+    int8_t  imat_dat    =  0; // whether the legacy imatrix.dat format should be output (gguf <= 0 < dat)
 
     bool process_output  = false; // collect data for the output tensor
     bool compute_ppl     = true;  // whether to compute perplexity