gh-153621: Expose raw libzstd error code in ZstdError messages

Include the raw error code returned by libzstd in all ZstdError messages, making it easier for users to diagnose compression and decompression issues.

Author: su-213

Modules/_zstd/_zstdmodule.c

@@ -67,45 +67,52 @@ set_zstd_error(const _zstd_state *state, error_type type, size_t zstd_ret)
     }
     switch (type) {
         case ERR_DECOMPRESS:
-            msg = "Unable to decompress Zstandard data: %s";
+            msg = "Unable to decompress Zstandard data: %s (error code %llu)";
             break;
         case ERR_COMPRESS:
-            msg = "Unable to compress Zstandard data: %s";
+            msg = "Unable to compress Zstandard data: %s (error code %llu)";
             break;
         case ERR_SET_PLEDGED_INPUT_SIZE:
-            msg = "Unable to set pledged uncompressed content size: %s";
+            msg = "Unable to set pledged uncompressed content size: %s "
+                  "(error code %llu)";
             break;
 
         case ERR_LOAD_D_DICT:
             msg = "Unable to load Zstandard dictionary or prefix for "
-                  "decompression: %s";
+                  "decompression: %s (error code %llu)";
             break;
         case ERR_LOAD_C_DICT:
             msg = "Unable to load Zstandard dictionary or prefix for "
-                  "compression: %s";
+                  "compression: %s (error code %llu)";
             break;
 
         case ERR_GET_C_BOUNDS:
-            msg = "Unable to get zstd compression parameter bounds: %s";
+            msg = "Unable to get zstd compression parameter bounds: %s "
+                  "(error code %llu)";
             break;
         case ERR_GET_D_BOUNDS:
-            msg = "Unable to get zstd decompression parameter bounds: %s";
+            msg = "Unable to get zstd decompression parameter bounds: %s "
+                  "(error code %llu)";
             break;
         case ERR_SET_C_LEVEL:
-            msg = "Unable to set zstd compression level: %s";
+            msg = "Unable to set zstd compression level: %s "
+                  "(error code %llu)";
             break;
 
         case ERR_TRAIN_DICT:
-            msg = "Unable to train the Zstandard dictionary: %s";
+            msg = "Unable to train the Zstandard dictionary: %s "
+                  "(error code %llu)";
             break;
         case ERR_FINALIZE_DICT:
-            msg = "Unable to finalize the Zstandard dictionary: %s";
+            msg = "Unable to finalize the Zstandard dictionary: %s "
+                  "(error code %llu)";
             break;
 
         default:
             Py_UNREACHABLE();
     }
-    PyErr_Format(state->ZstdError, msg, ZSTD_getErrorName(zstd_ret));
+    PyErr_Format(state->ZstdError, msg, ZSTD_getErrorName(zstd_ret),
+                 (unsigned long long)zstd_ret);
 }
 
 typedef struct {