[mlir][sparse] Fixing case coverage warning

[wrengr]

Summary

Followup to D133835 for fixing the warning on LLVM's Windows buildbot

[stella.stamenova]

Thanks!

[NathanielMcVicar]

It looks like the File.cpp fix was reverted due to producing a different warning, reintroducing the MSVC one here: https://github.com/llvm/llvm-project/commit/e898be2f6edbb886af2f6b23e2f5db5210535620.

https://lab.llvm.org/buildbot/#/builders/13/builds/26533

C:\buildbot\mlir-x64-windows-ninja\llvm-project\mlir\lib\ExecutionEngine\SparseTensor\File.cpp(111) : warning C4715: 'mlir::sparse_tensor::SparseTensorFile::canReadAs': not all control paths return a value

mlir/include/mlir/ExecutionEngine/SparseTensor/File.h

 // TODO: consider distinguishing separate classes for before vs
 // after reading the header; so as to statically avoid the need
 // to `assert(isValid())`.
 
 /// This class abstracts over the information stored in file headers,
 /// as well as providing the buffers and methods for parsing those headers.
 class SparseTensorFile final {
 public:
-  enum class ValueKind {
+  enum class ValueKind : uint8_t {
     // The value before calling `readHeader`.
     kInvalid = 0,
     // Values that can be set by `readMMEHeader`.
     kPattern = 1,
     kReal = 2,
     kInteger = 3,
     kComplex = 4,
     // The value set by `readExtFROSTTHeader`.

mlir/lib/ExecutionEngine/SparseTensor/File.cpp

case ValueKind::kComplex:
     // When the file is specified to store complex values, then we
     // require a complex primary-type.
     return isComplexPrimaryType(valTy);
   case ValueKind::kUndefined:
     // The "extended" FROSTT format doesn't specify a ValueKind.
     // So we allow implicitly converting the stored values to both
     // integer and floating primary-types.
     return isRealPrimaryType(valTy);
+  default:
+    MLIR_SPARSETENSOR_FATAL("Unknown ValueKind: %d\n",
+                            static_cast<uint8_t>(valueKind_));
   }
 }
 
 /// Helper to convert C-style strings (i.e., '\0' terminated) to lower case.
 static inline char *toLower(char *token) {
   for (char *c = token; *c; ++c)
     *c = tolower(*c);
   return token;