Fix output for empty interfaces. Added a test.

Author: balshetzer

mockgen/mockgen.go

@@ -231,7 +231,15 @@ func (g *generator) Generate(pkg *model.Package, pkgName string, outputPackagePa
 	// Get all required imports, and generate unique names for them all.
 	im := pkg.Imports()
 	im[gomockImportPath] = true
-	im["reflect"] = true
+
+	// Only import reflect if it's used. We only use reflect in mocked methods
+	// so only import if any of the mocked interfaces have methods.
+	for _, intf := range pkg.Interfaces {
+		if len(intf.Methods) > 0 {
+			im["reflect"] = true
+			break
+		}
+	}
 
 	// Sort keys to make import alias generation predictable
 	sorted_paths := make([]string, len(im), len(im))

mockgen/tests/empty_interface/input.go

@@ -0,0 +1,4 @@
+//go:generate mockgen -package empty_interface -destination mock.go -source input.go
+package empty_interface
+
+type Empty interface{}