support custom errors with arguments

ethers/errors.nim

@@ -1,3 +1,4 @@
+import pkg/contractabi
 import pkg/contractabi/selector
 import ./basics
 
@@ -7,14 +8,33 @@ type SolidityError* = object of EthersError
 
 template errors*(types) {.pragma.}
 
+func selector(E: type): FunctionSelector =
+  when compiles(E.arguments):
+    selector($E, typeof(E.arguments))
+  else:
+    selector($E, tuple[])
+
+func matchesSelector(E: type, data: seq[byte]): bool =
+  const selector = E.selector.toArray
+  data.len >= 4 and selector[0..<4] == data[0..<4]
+
+func decodeArguments(E: type, data: seq[byte]): auto =
+  AbiDecoder.decode(data[4..^1], E.arguments)
+
 func decode*[E: SolidityError](_: type E, data: seq[byte]): ?!(ref E) =
-  const name = $E
+  if not E.matchesSelector(data):
-  const selector = selector(name, typeof(()))
+    return failure "unable to decode " & $E & ": selector doesn't match"
-  if data.len < 4:
+  when compiles(E.arguments):
-    return failure "unable to decode " & name & ": signature too short"
+    without arguments =? E.decodeArguments(data), error:
-  if selector.toArray[0..<4] != data[0..<4]:
+      return failure "unable to decode " & $E & ": " & error.msg
-    return failure "unable to decode " & name & ": signature doesn't match"
+    success (ref E)(arguments: arguments)
-  success (ref E)()
+  else:
+    success (ref E)()
+
+func encode*[E: SolidityError](_: type AbiEncoder, error: ref E): seq[byte] =
+  result = @(E.selector.toArray)
+  when compiles(error.arguments):
+    result &= AbiEncoder.encode(error.arguments)
 
 template convertCustomErrors*[ErrorTypes: tuple](body: untyped): untyped =
   try:

testmodule/testCustomErrors.nim

@@ -8,6 +8,8 @@ suite "Contract custom errors":
   type
     TestCustomErrors = ref object of Contract
     SimpleError = object of SolidityError
+    ErrorWithArguments = object of SolidityError
+      arguments: tuple[one: UInt256, two: bool]
 
   var contract: TestCustomErrors
   var provider: JsonRpcProvider
@@ -30,3 +32,14 @@ suite "Contract custom errors":
 
     expect SimpleError:
       await contract.revertsSimpleError()
+
+  test "handles error with arguments":
+    proc revertsErrorWithArguments(contract: TestCustomErrors)
+      {.contract, pure, errors:[ErrorWithArguments].}
+
+    try:
+      await contract.revertsErrorWithArguments()
+      fail()
+    except ErrorWithArguments as error:
+      check error.arguments.one == 1
+      check error.arguments.two == true

testmodule/testErrorDecoding.nim

@@ -1,10 +1,14 @@
 import std/unittest
 import pkg/questionable/results
+import pkg/contractabi
 import pkg/ethers/errors
 
 suite "Decoding of custom errors":
 
-  type SimpleError = object of SolidityError
+  type
+    SimpleError = object of SolidityError
+    ErrorWithArguments = object of SolidityError
+      arguments: tuple[one: UInt256, two: bool]
 
   test "decodes a simple error":
     let decoded = SimpleError.decode(@[0xc2'u8, 0xbb, 0x94, 0x7c])
@@ -12,6 +16,14 @@ suite "Decoding of custom errors":
     check decoded.isSuccess
     check (!decoded) != nil
 
+  test "decodes error with arguments":
+    let expected = (ref ErrorWithArguments)(arguments: (1.u256, true))
+    let encoded = AbiEncoder.encode(expected)
+    let decoded = ErrorWithArguments.decode(encoded)
+    check decoded.isSuccess
+    check (!decoded).arguments.one == 1.u256
+    check (!decoded).arguments.two == true
+
   test "returns failure when decoding fails":
     let invalid = @[0xc2'u8, 0xbb, 0x94, 0x0] # last byte is wrong
     let decoded = SimpleError.decode(invalid)