fix(precompile): better error msgs (#921)

@ocnc

.gitignore

@@ -226,3 +226,4 @@ out
 
 # integration testing coverage
 coverage-testunitcover.txt
+coverage-teste2ecover.txt

e2e/localnet/go.sum

@@ -189,6 +189,7 @@ github.com/cosmos/cosmos-db v1.0.0/go.mod h1:iBvi1TtqaedwLdcrZVYRSSCb6eSy61NLj4U
 github.com/cosmos/cosmos-proto v1.0.0-beta.3 h1:VitvZ1lPORTVxkmF2fAp3IiA61xVwArQYKXTdEcpW6o=
 github.com/cosmos/cosmos-proto v1.0.0-beta.3/go.mod h1:t8IASdLaAq+bbHbjq4p960BvcTqtwuAxid3b/2rOD6I=
 github.com/cosmos/cosmos-sdk v0.50.0-beta.0.0.20230727121850-bd61e84ef162 h1:jYNPV5xfv3bsH+B6y1qxo2ru2cKz+1vJQqSa7L86byQ=
+github.com/cosmos/cosmos-sdk v0.50.0-beta.0.0.20230727121850-bd61e84ef162/go.mod h1:MF/wnXyreoL0g8YdRZhUD4apPdgebMc29LgMJB+dh6M=
 github.com/cosmos/go-bip39 v1.0.0 h1:pcomnQdrdH22njcAatO0yWojsUnCO3y2tNoV1cb6hHY=
 github.com/cosmos/go-bip39 v1.0.0/go.mod h1:RNJv0H/pOIVgxw6KS7QeX2a0Uo0aKUlfhZ4xuwvCdJw=
 github.com/cosmos/gogogateway v1.2.0 h1:Ae/OivNhp8DqBi/sh2A8a1D0y638GpL3tkmLQAiKxTE=

eth/core/precompile/method_validation.go

@@ -136,7 +136,12 @@ func validateOutputs(implMethod reflect.Method, abiMethod *abi.Method) error {
 
 	// Last parameter of Go precompile implementation is an error (for reverts), so we skip that.
 	if implMethodNumOut-1 != len(abiMethod.Outputs) {
-		return errors.New("number of return types mismatch")
+		return fmt.Errorf(
+			"number of return args mismatch: %v expects %v return vals, %v returns %v vals",
+			abiMethod.Name,
+			len(abiMethod.Outputs),
+			implMethod.Name, implMethodNumOut-1,
+		)
 	}
 
 	// Validate that our implementation returns an error (revert) as the last param.
@@ -154,7 +159,11 @@ func validateOutputs(implMethod reflect.Method, abiMethod *abi.Method) error {
 			reflect.New(implMethodReturnType).Elem(), reflect.New(abiMethodReturnType).Elem(),
 		); err != nil {
 			return fmt.Errorf(
-				"return type mismatch: %v != %v", implMethodReturnType, abiMethodReturnType,
+				"return type mismatch: %v expects %v, %v has %v",
+				abiMethod.Name,
+				abiMethodReturnType,
+				implMethod.Name,
+				implMethodReturnType,
 			)
 		}
 	}

eth/core/precompile/method_validation_test.go

@@ -151,12 +151,12 @@ var _ = Describe("Method", func() {
 			numReturnMismatch, found := reflect.TypeOf(m).MethodByName("NumReturnMismatch")
 			Expect(found).To(BeTrue())
 			Expect(validateOutputs(numReturnMismatch, &exampleFunc).Error()).To(Equal(
-				"number of return types mismatch"))
+				"number of return args mismatch: exampleFunc expects 1 return vals, NumReturnMismatch returns 0 vals"))
 
 			returnTypeMismatch, found := reflect.TypeOf(m).MethodByName("ReturnTypeMismatch")
 			Expect(found).To(BeTrue())
 			Expect(validateOutputs(returnTypeMismatch, &exampleFunc).Error()).To(Equal(
-				"return type mismatch: string != bool"))
+				"return type mismatch: exampleFunc expects bool, ReturnTypeMismatch has string"))
 		})
 	})