feat(scaffolding): improve Go function signature detection (#3125)

* fix/typed-error

* fix/testing

Author: intojhanurag

pkg/scaffolding/detectors.go

@@ -10,6 +10,14 @@ import (
 	"strings"
 )
 
+type SignatureError struct {
+	Msg string
+}
+
+func (e *SignatureError) Error() string {
+	return fmt.Sprintf("signature detection error: %s", e.Msg)
+}
+
 // detector of method signatures.  Each instance is for a given runtime.
 type detector interface {
 	Detect(dir string) (static, instanced bool, err error)
@@ -58,7 +66,13 @@ func (d goDetector) Detect(dir string) (static, instanced bool, err error) {
 			static = true
 		}
 	}
-	return
+	if static && instanced {
+		return static, instanced, &SignatureError{Msg: "both static and instanced signatures found"}
+	}
+	if !static && !instanced {
+		return static, instanced, &SignatureError{Msg: "no signatures found"}
+	}
+	return static, instanced, nil
 }
 
 func (d goDetector) hasFunctionDeclaration(filename, function string) bool {

pkg/scaffolding/detectors_test.go

@@ -67,7 +67,7 @@ func Handle() { }
 		{
 			Name: "Static and Instanced - error",
 			Sig:  UnknownSignature,
-			Err:  errors.New("error expected"), // TODO: typed error and err.Is/As
+			Err:  errors.New("error expected"),
 			Src: `
 package f
 func Handle() { }
@@ -76,7 +76,7 @@ func New() { }
 		{
 			Name: "No Signatures Found - error",
 			Sig:  UnknownSignature,
-			Err:  errors.New("error expected"), // TODO: typed error and err.Is/As
+			Err:  errors.New("error expected"),
 			Src: `
 package f
 // Intentionally Blank
@@ -127,10 +127,11 @@ func (f *MyFunction) Handle() {}
 			}
 
 			if test.Err != nil {
-				if err == nil {
-					t.Fatal("expected error not received")
+				var sigErr *SignatureError
+				if !errors.As(err, &sigErr) {
+					t.Fatalf("expected SignatureError, got:%v", err)
 				} else {
-					t.Logf("received expected error: %v", err)
+					t.Logf("received expected error: %v", sigErr)
 				}
 			}