template: OnlyExcept skipping

template/template.go

@@ -125,6 +125,31 @@ func (t *Template) Validate() error {
 	return err
 }
 
+// Skip says whether or not to skip the build with the given name.
+func (o *OnlyExcept) Skip(n string) bool {
+	if len(o.Only) > 0 {
+		for _, v := range o.Only {
+			if v == n {
+				return false
+			}
+		}
+
+		return true
+	}
+
+	if len(o.Except) > 0 {
+		for _, v := range o.Except {
+			if v == n {
+				return true
+			}
+		}
+
+		return false
+	}
+
+	return false
+}
+
 // Validate validates that the OnlyExcept settings are correct for a thing.
 func (o *OnlyExcept) Validate(t *Template) error {
 	if len(o.Only) > 0 && len(o.Except) > 0 {

template/template_test.go

@@ -92,3 +92,46 @@ func TestTemplateValidate(t *testing.T) {
 		}
 	}
 }
+
+func TestOnlyExceptSkip(t *testing.T) {
+	cases := []struct {
+		Only, Except []string
+		Input        string
+		Result       bool
+	}{
+		{
+			[]string{"foo"},
+			nil,
+			"foo",
+			false,
+		},
+
+		{
+			nil,
+			[]string{"foo"},
+			"foo",
+			true,
+		},
+
+		{
+			nil,
+			nil,
+			"foo",
+			false,
+		},
+	}
+
+	for _, tc := range cases {
+		oe := &OnlyExcept{
+			Only:   tc.Only,
+			Except: tc.Except,
+		}
+
+		actual := oe.Skip(tc.Input)
+		if actual != tc.Result {
+			t.Fatalf(
+				"bad: %#v\n\n%#v\n\n%#v\n\n%#v",
+				actual, tc.Only, tc.Except, tc.Input)
+		}
+	}
+}