fix(clang-tidy): fix issues it found in CI

Curiously, the changed includes seem to allow `clang-tidy` to see issues
that it previously didn't see. This commit fixes them.

Signed-off-by: Ingo Müller <ingomueller@google.com>

Author: ingomueller-net

include/substrait/common/Exceptions.h

@@ -36,7 +36,7 @@ inline constexpr const char* kNotImplemented = "NOT_IMPLEMENTED";
 
 class SubstraitException : public std::exception {
  public:
-  enum class Type {
+  enum class Type : int8_t {
     // Errors where the root cause of the problem is either because of bad input
     // or an unsupported pattern of use are classified with USER. Examples
     // of errors in this category include syntax errors, unavailable names or

include/substrait/common/Io.h

@@ -15,7 +15,7 @@ namespace io::substrait {
 /*
  * \brief The four different ways plans can be represented on disk.
  */
-enum class PlanFileFormat {
+enum class PlanFileFormat : int8_t {
   kBinary = 0,
   kJson = 1,
   kProtoText = 2,

include/substrait/expression/DecimalLiteral.h

@@ -7,7 +7,7 @@
 #include <utility>
 
 namespace substrait::proto {
-class Expression_Literal_Decimal;
+class Expression_Literal_Decimal; // NOLINT
 }
 
 namespace io::substrait::expression {

src/substrait/textplan/Location.h

@@ -7,9 +7,9 @@
 
 namespace std {
 template <typename>
-struct less;
+struct less; // NOLINT
 template <typename>
-struct hash;
+struct hash; // NOLINT
 } // namespace std
 
 namespace antlr4 {

src/substrait/textplan/SymbolTable.h

@@ -19,7 +19,7 @@
 
 namespace io::substrait::textplan {
 
-enum class SymbolType {
+enum class SymbolType : int8_t {
   kExtensionSpace = 0,
   kFunction = 1,
   kPlanRelation = 2,
@@ -36,7 +36,7 @@ enum class SymbolType {
   kUnknown = -1,
 };
 
-enum class RelationType {
+enum class RelationType : int8_t {
   // Logical
   kUnknown = 0,
   kRead = 1,
@@ -64,12 +64,12 @@ enum class RelationType {
   kExtensionMulti = 102,
 };
 
-enum class RelationDetailType {
+enum class RelationDetailType : int8_t {
   kUnknown = 0,
   kExpression = 1,
 };
 
-enum class SourceType {
+enum class SourceType : int8_t {
   kUnknown = 0,
   kLocalFiles = 1,
   kNamedTable = 2,
@@ -81,7 +81,7 @@ const std::string& symbolTypeName(SymbolType type);
 
 struct SymbolInfo {
   std::string name;
-  std::string alias{}; // If present, use this instead of name.
+  std::string alias; // If present, use this instead of name.
   const SymbolInfo* schema{nullptr}; // The related schema symbol if present.
   Location sourceLocation;
   Location permanentLocation{Location::kUnknownLocation};