internal: Abstract time with fxclock

Add an internal fxclock package that provides a minimal Clock interface.

We will use this to abstract away Fx's use of time operations to help
address test flakiness issues.

go.mod

@@ -3,6 +3,7 @@ module go.uber.org/fx
 go 1.13
 
 require (
+	github.com/benbjohnson/clock v1.3.0
 	github.com/stretchr/testify v1.7.0
 	go.uber.org/dig v1.12.0
 	go.uber.org/goleak v1.1.11

go.sum

@@ -1,5 +1,7 @@
 github.com/BurntSushi/toml v0.3.1 h1:WXkYYl6Yr3qBf1K79EBnL4mak0OimBfB0XUf9Vl28OQ=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
+github.com/benbjohnson/clock v1.3.0 h1:ip6w0uFQkncKQ979AypyG0ER7mqUSBdKLOgAle/AT8A=
+github.com/benbjohnson/clock v1.3.0/go.mod h1:J11/hYXuz8f4ySSvYwY0FKfm+ezbsZBKZxNJlLklBHA=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=

internal/fxclock/clock.go

@@ -0,0 +1,58 @@
+// Copyright (c) 2021 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package fxclock
+
+import (
+	"context"
+	"time"
+)
+
+// Clock defines how Fx accesses time.
+// The interface is pretty minimal but it matches github.com/benbjohnson/clock.
+// We intentionally don't use that interface directly;
+// this keeps it a test dependency for us.
+type Clock interface {
+	Now() time.Time
+	Since(time.Time) time.Duration
+	Sleep(time.Duration)
+	WithTimeout(context.Context, time.Duration) (context.Context, context.CancelFunc)
+}
+
+// System is the default implementation of Clock based on real time.
+var System Clock = systemClock{}
+
+type systemClock struct{}
+
+func (systemClock) Now() time.Time {
+	return time.Now()
+}
+
+func (systemClock) Since(t time.Time) time.Duration {
+	return time.Since(t)
+}
+
+func (systemClock) Sleep(d time.Duration) {
+	time.Sleep(d)
+}
+
+func (systemClock) WithTimeout(ctx context.Context, d time.Duration) (context.Context, context.CancelFunc) {
+	return context.WithTimeout(ctx, d)
+}

internal/fxclock/clock_test.go

@@ -0,0 +1,65 @@
+// Copyright (c) 2021 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package fxclock
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/benbjohnson/clock"
+	"github.com/stretchr/testify/assert"
+)
+
+var _ Clock = clock.Clock(nil)
+
+// Just a basic sanity check that everything is in order.
+func TestSystemClock(t *testing.T) {
+	t.Parallel()
+
+	clock := System
+
+	t.Run("Now and Since", func(t *testing.T) {
+		t.Parallel()
+
+		before := clock.Now()
+		assert.GreaterOrEqual(t, clock.Since(before), time.Duration(0))
+	})
+
+	t.Run("Sleep", func(t *testing.T) {
+		t.Parallel()
+
+		assert.NotPanics(t, func() {
+			clock.Sleep(time.Millisecond)
+		})
+	})
+
+	t.Run("WithTimeout", func(t *testing.T) {
+		t.Parallel()
+
+		ctx := context.Background()
+		ctx, cancel := clock.WithTimeout(ctx, time.Second)
+		defer cancel()
+
+		_, ok := ctx.Deadline()
+		assert.True(t, ok, "must have deadline")
+	})
+}