Add panicx.LocationOfMethod().

engine/panicx/linenumber_test.go

@@ -51,3 +51,7 @@ func doNothing()                     {}
 func panicWithUnexpectedMessage()    { panic(dogma.UnexpectedMessage) }
 func locationOfCallLayer1() Location { return LocationOfCall() }
 func locationOfCallLayer2() Location { return locationOfCallLayer1() }
+
+type locationOfMethodT struct{}
+
+func (locationOfMethodT) Method() {}

engine/panicx/location.go

@@ -42,7 +42,10 @@ func (l Location) String() string {
 
 // LocationOfFunc returns the location of the definition of fn.
 func LocationOfFunc(fn interface{}) Location {
-	rv := reflect.ValueOf(fn)
+	return locationOfFunc(reflect.ValueOf(fn))
+}
+
+func locationOfFunc(rv reflect.Value) Location {
 	if rv.Kind() != reflect.Func {
 		panic("fn must be a function")
 	}
@@ -60,6 +63,18 @@ func LocationOfFunc(fn interface{}) Location {
 	return loc
 }
 
+// LocationOfMethod returns the location of the definition of fn.
+func LocationOfMethod(recv interface{}, m string) Location {
+	rt := reflect.TypeOf(recv)
+
+	rm, ok := rt.MethodByName(m)
+	if !ok {
+		panic("method does not exist")
+	}
+
+	return locationOfFunc(rm.Func)
+}
+
 // LocationOfCall returns the location where its caller was called itself.
 func LocationOfCall() Location {
 	var loc Location

engine/panicx/location_test.go

@@ -29,6 +29,20 @@ var _ = Describe("type Location", func() {
 		})
 	})
 
+	Describe("func LocationOfMethod()", func() {
+		It("returns the expected location", func() {
+			loc := LocationOfMethod(locationOfMethodT{}, "Method")
+
+			Expect(loc).To(MatchAllFields(
+				Fields{
+					"Func": Equal("github.com/dogmatiq/testkit/engine/panicx_test.locationOfMethodT.Method"),
+					"File": HaveSuffix("/engine/panicx/linenumber_test.go"),
+					"Line": Equal(57),
+				},
+			))
+		})
+	})
+
 	Describe("func LocationOfCall()", func() {
 		It("returns the expected location", func() {
 			loc := locationOfCallLayer2()