[MLIR][ODS] Add support for wrapping enums with std::optional in Type/Attr definitions (#117719)

Author: joker-eph

mlir/test/lib/Dialect/Test/TestAttrDefs.td

@@ -226,6 +226,12 @@ def TestAttrWithOptionalUnsigned : Test_Attr<"TestAttrWithOptionalUnsigned"> {
   let mnemonic = "attr_with_optional_unsigned";
 }
 
+def TestAttrWithOptionalEnum : Test_Attr<"TestAttrWithOptionalEnum"> {
+  let parameters = (ins OptionalParameter<"std::optional<SimpleEnum>">:$value);
+  let assemblyFormat = "`<` $value `>`";
+  let mnemonic = "attr_with_optional_enum";
+}
+
 def TestAttrUgly : Test_Attr<"TestAttrUgly"> {
   let parameters = (ins "::mlir::Attribute":$attr);
 

mlir/test/mlir-tblgen/attr-or-type-format-roundtrip.mlir

@@ -26,7 +26,13 @@ attributes {
   // CHECK: #test.attr_with_optional_signed<-9223372036854775808>
   attr9 = #test.attr_with_optional_signed<-9223372036854775808>,
   // CHECK: #test.attr_with_optional_unsigned<18446744073709551615>
-  attr_10 = #test.attr_with_optional_unsigned<18446744073709551615>
+  attr_10 = #test.attr_with_optional_unsigned<18446744073709551615>,
+  // CHECK: #test.attr_with_optional_enum<>
+  attr_11 = #test.attr_with_optional_enum<>,
+  // CHECK: #test.attr_with_optional_enum<a>
+  attr_12 = #test.attr_with_optional_enum<a>,
+  // CHECK: #test.attr_with_optional_enum<b>
+  attr_13 = #test.attr_with_optional_enum<b>
 }
 
 // CHECK-LABEL: @test_roundtrip_default_parsers_struct

mlir/tools/mlir-tblgen/EnumsGen.cpp

@@ -101,6 +101,27 @@ struct FieldParser<{0}, {0}> {{
     return parser.emitError(loc, "invalid {2} specification: ") << enumKeyword;
   }
 };
+
+/// Support for std::optional, useful in attribute/type definition where the enum is
+/// used as:
+///
+///    let parameters = (ins OptionalParameter<"std::optional<TheEnumName>">:$value);
+template<>
+struct FieldParser<std::optional<{0}>, std::optional<{0}>> {{
+  template <typename ParserT>
+  static FailureOr<std::optional<{0}>> parse(ParserT &parser) {{
+    // Parse the keyword/string containing the enum.
+    std::string enumKeyword;
+    auto loc = parser.getCurrentLocation();
+    if (failed(parser.parseOptionalKeywordOrString(&enumKeyword)))
+      return std::optional<{0}>{{};
+
+    // Symbolize the keyword.
+    if (::std::optional<{0}> attr = {1}::symbolizeEnum<{0}>(enumKeyword))
+      return attr;
+    return parser.emitError(loc, "invalid {2} specification: ") << enumKeyword;
+  }
+};
 } // namespace mlir
 
 namespace llvm {