Report function signature declaration using variable name other than err

I had previously hard-coded the variable name "err" as the recommended
name declaration in the function signature for simplicity.

Now, use the name assigned in the `defer` instead, which is more
correct.

2 files changed, 17 insertions, 2 deletions

diff --git a/defererr.go b/defererr.go
index 96072be..f6167ae 100644
--- a/defererr.go
+++ b/defererr.go
@@ -334,8 +334,8 @@ func checkErrorAssignedInDefer(
 					if !isErrorNameInReturnSignature {
 						pass.Reportf(
 							errorReturnField.Pos(),
-							"return signature should be '(err error)'", // TODO: Use name from ident.Name
-							// errorReturnField,
+							"return signature should be '(%s error)'", // TODO: Use name from ident.Name
+							ident,
 						)
 
 						break
diff --git a/testdata/signature.go b/testdata/signature.go
index 73203ee..b668558 100644
--- a/testdata/signature.go
+++ b/testdata/signature.go
@@ -45,6 +45,21 @@ func returnedErrorMustMatchDeferErrorName() (err error) {
 	return err2 // want "does not return 'err'"
 }
 
+func deferUsesUnconventionalErrName() error { // want "return signature should be '\\(anErr error\\)'"
+	var anErr error
+
+	anErr = nil
+	if anErr != nil {
+		return anErr
+	}
+
+	defer func() {
+		anErr = errors.New("defer error")
+	}()
+
+	return anErr
+}
+
 func good() (err error) {
 	err = nil
 	if err != nil {