Custom parser/printer for header fields

Author: PietroGhg

include/p4mlir/Dialect/BMv2IR/BMv2IR_Types.td

@@ -16,6 +16,18 @@ class BMv2IR_Type<string name, string typeMnemonic, list<Trait> traits = []>
   let mnemonic = typeMnemonic;
 }
 
+// We use a custom parameter here to allow for an empty array of fields
+def FieldInfoArrayParameter : ArrayRefParameter<"BMv2IR::FieldInfo", "struct fields"> {
+  let parser = "::mlir::FieldParser<::llvm::ArrayRef<BMv2IR::FieldInfo>>::parse($_parser)";
+  let printer = [{
+     $_printer << '[';
+     llvm::interleaveComma($_self, $_printer, [&](BMv2IR::FieldInfo field) {
+         $_printer << field;
+     });
+     $_printer << ']';
+   }];
+}
+
 def BMv2IR_HeaderType : BMv2IR_Type<"Header", "header"> {
   let summary = "BMv2 header type";
   let description = [{
@@ -32,12 +44,12 @@ def BMv2IR_HeaderType : BMv2IR_Type<"Header", "header"> {
 
   let parameters = (ins
     StringRefParameter<"struct name">:$name,
-    ArrayRefParameter<"BMv2IR::FieldInfo", "struct fields">:$fields,
+    FieldInfoArrayParameter:$fields,
     OptionalParameter<"unsigned">:$max_length
   );
 
   let assemblyFormat = [{
-    `<` $name `,` `[` $fields `]`
+    `<` $name `,` $fields
     (`,` `max_length` `=` $max_length^)?
     `>`
   }];

lib/Dialect/BMv2IR/BMv2IR_Types.cpp

@@ -29,6 +29,28 @@ struct mlir::FieldParser<P4::P4MLIR::BMv2IR::FieldInfo> {
     }
 };
 
+// Custom parser that allows an empty array of fields
+template <>
+struct mlir::FieldParser<llvm::ArrayRef<P4::P4MLIR::BMv2IR::FieldInfo>> {
+    static FailureOr<llvm::SmallVector<P4::P4MLIR::BMv2IR::FieldInfo>> parse(AsmParser &parser) {
+        llvm::SmallVector<P4::P4MLIR::BMv2IR::FieldInfo> result;
+
+        if (parser.parseLSquare()) return failure();
+
+        if (succeeded(parser.parseOptionalRSquare())) return result;
+
+        do {
+            auto field = FieldParser<BMv2IR::FieldInfo>::parse(parser);
+            if (failed(field)) return failure();
+            result.push_back(*field);
+        } while (succeeded(parser.parseOptionalComma()));
+
+        if (parser.parseRSquare()) return failure();
+
+        return result;
+    }
+};
+
 constexpr unsigned bitsInByte = 8;
 static unsigned computeTotalHeaderLenghtInBits(ArrayRef<BMv2IR::FieldInfo> fields) {
     unsigned total = 0;

test/Targets/BMv2/parser.mlir

@@ -572,3 +572,24 @@ module {
 // CHECK-NEXT:      ]
 // CHECK-NEXT:    }
 // CHECK-NEXT:  ],
+
+// -----
+
+module {
+  bmv2ir.header_instance @H_ipv4 : !bmv2ir.header<"ipv4_t", []>
+}
+
+// CHECK:  "header_types": [
+// CHECK:    {
+// CHECK:      "fields": [],
+// CHECK:      "id": 0,
+// CHECK:      "name": "ipv4_t"
+// CHECK:    }
+// CHECK:  ],
+// CHECK:  "headers": [
+// CHECK:    {
+// CHECK:      "header_type": "ipv4_t",
+// CHECK:      "id": 0,
+// CHECK:      "metadata": false,
+// CHECK:      "name": "H_ipv4"
+// CHECK:    }