[Error Message] Improve the error message (#1342)

* patch

* fix+1

* add readme

* fix error message

src/kernel/common.h

@@ -9,6 +9,7 @@
 #include <dgl/runtime/ndarray.h>
 
 #include <cstdint>
+#include "../c_api_common.h"
 
 namespace dgl {
 namespace kernel {
@@ -48,10 +49,9 @@ namespace kernel {
 #define DGL_DTYPE_SWITCH(val, DType, ...)       \
   if (val.code == kDLFloat && val.bits == 32) { \
     typedef float DType;                        \
-    {__VA_ARGS__}                                           \
+    { __VA_ARGS__ }                             \
   } else {                                      \
-    LOG(FATAL) << "Unsupported dtype: " << val.code << "_"  \
-               << val.bits;                                 \
+    LOG(FATAL) << "Unsupported dtype: " << val; \
   }
 
 // Macro for unrolling with data type arguments.

src/runtime/c_runtime_api.cc

@@ -85,7 +85,7 @@ class DeviceAPIManager {
     auto* f = Registry::Get(factory);
     if (f == nullptr) {
       CHECK(allow_missing)
-          << "Device API " << name << " is not enabled.";
+          << "Device API " << name << " is not enabled. Please install the cuda version of dgl.";
       return nullptr;
     }
     void* ptr = (*f)();