Report when error declaration in signature is needed

While looking at the assignments in the `defer`, if we encounter an
`error`-type assignment, emit a diagnostic if the error named in the lhs
of the assignment is not present in the return signature's names.

Not sure if this makes sense to me yet. I probably only want to report a
problem for a non-declare assignment of an error value when the error
type in the return signature is _not_ named at all.

2 files changed, 38 insertions, 1 deletions

diff --git a/defererr.go b/defererr.go
index 338f2c1..8d1cb51 100644
--- a/defererr.go
+++ b/defererr.go
@@ -62,6 +62,7 @@ func run(pass *analysis.Pass) (interface{}, error) {
 				if len(funcDecl.Type.Results.List[errorReturnIndex].Names) > 0 {
 					fmt.Printf("return error var name: %#v\n", funcDecl.Type.Results.List[errorReturnIndex].Names[0])
 				}
+				errorReturnField := funcDecl.Type.Results.List[errorReturnIndex]
 
 				ast.Inspect(
 					funcDecl.Body,
@@ -133,6 +134,25 @@ func run(pass *analysis.Pass) (interface{}, error) {
 
 									if named.Obj().Name() == "error" {
 										deferAssignsError = true
+
+										isErrorNameInReturnSignature := false
+
+										for _, errorReturnIdent := range errorReturnField.Names {
+											if ident.Name == errorReturnIdent.Name {
+												// Report if no matches
+												isErrorNameInReturnSignature = true
+											}
+										}
+
+										if !isErrorNameInReturnSignature {
+											pass.Reportf(
+												errorReturnField.Pos(),
+												"return signature should be '(err error)'", // TODO: Use name from ident.Name
+												// errorReturnField,
+											)
+
+											break
+										}
 									}
 								}
 
@@ -142,6 +162,23 @@ func run(pass *analysis.Pass) (interface{}, error) {
 
 								// TODO: Check that funcDecl declares error in signature (check before ast.Inspect on function body, report here)
 
+								// isErrorNameInReturnSignature := false
+								//
+								// for _, errorReturnIdent := range errorReturnField.Names {
+								// 	if ident.Name == errorReturnIdent.Name {
+								// 		// Report if no matches
+								// 		isErrorNameInReturnSignature = true
+								// 	}
+								// }
+								//
+								// if !isErrorNameInReturnSignature {
+								// 	pass.Reportf(
+								// 		errorReturnField.Pos(),
+								// 		"return signature should be '(err error)' (TODO)",
+								// 		errorReturnField,
+								// 	)
+								// }
+
 								return true
 							},
 						)
diff --git a/testdata/signature.go b/testdata/signature.go
index 6fc15fc..d780240 100644
--- a/testdata/signature.go
+++ b/testdata/signature.go
@@ -2,7 +2,7 @@ package main
 
 import "errors"
 
-func shouldDeclareErrInSignature() error { // want "return signature should be '(err error)'"
+func shouldDeclareErrInSignature() error { // want "return signature should be '\\(err error\\)'"
 	var err error // Should use variable declared in signature
 
 	err = nil