Fix cache miss when builtin build args are used.

Signed-off-by: Daniel Nephin <dnephin@docker.com>

builder/dockerfile/dispatchers.go

@@ -395,9 +395,7 @@ func run(req dispatchRequest) error {
 	// that starts with "foo=abc" to be considered part of a build-time env var.
 	saveCmd := config.Cmd
 	if len(cmdBuildEnv) > 0 {
-		sort.Strings(cmdBuildEnv)
-		tmpEnv := append([]string{fmt.Sprintf("|%d", len(cmdBuildEnv))}, cmdBuildEnv...)
-		saveCmd = strslice.StrSlice(append(tmpEnv, saveCmd...))
+		saveCmd = prependEnvOnCmd(req.builder.buildArgs, cmdBuildEnv, saveCmd)
 	}
 
 	req.runConfig.Cmd = saveCmd
@@ -434,25 +432,24 @@ func run(req dispatchRequest) error {
 	// properly match it.
 	req.runConfig.Env = env
 
-	// remove builtinAllowedBuildArgs (see: builder.go)  from the saveCmd
-	// these args are transparent so resulting image should be the same regardless of the value
-	if len(cmdBuildEnv) > 0 {
-		saveCmd = config.Cmd
-		var tmpBuildEnv []string
-		for _, env := range cmdBuildEnv {
-			key := strings.SplitN(env, "=", 2)[0]
-			if !req.builder.buildArgs.IsUnreferencedBuiltin(key) {
-				tmpBuildEnv = append(tmpBuildEnv, env)
-			}
-		}
-		sort.Strings(tmpBuildEnv)
-		tmpEnv := append([]string{fmt.Sprintf("|%d", len(tmpBuildEnv))}, tmpBuildEnv...)
-		saveCmd = strslice.StrSlice(append(tmpEnv, saveCmd...))
-	}
 	req.runConfig.Cmd = saveCmd
 	return req.builder.commitContainer(cID, copyRunConfig(req.runConfig, withCmd(cmd)))
 }
 
+func prependEnvOnCmd(buildArgs *buildArgs, buildArgVars []string, cmd strslice.StrSlice) strslice.StrSlice {
+	var tmpBuildEnv []string
+	for _, env := range buildArgVars {
+		key := strings.SplitN(env, "=", 2)[0]
+		if !buildArgs.IsUnreferencedBuiltin(key) {
+			tmpBuildEnv = append(tmpBuildEnv, env)
+		}
+	}
+
+	sort.Strings(tmpBuildEnv)
+	tmpEnv := append([]string{fmt.Sprintf("|%d", len(tmpBuildEnv))}, tmpBuildEnv...)
+	return strslice.StrSlice(append(tmpEnv, cmd...))
+}
+
 // CMD foo
 //
 // Set the default command to run in the container (which may be empty).

integration-cli/docker_cli_build_test.go

@@ -4354,15 +4354,22 @@ func (s *DockerSuite) TestBuildTimeArgHistoryExclusions(c *check.C) {
 		ARG %s
 		ARG %s
 		RUN echo "Testing Build Args!"`, envKey, explicitProxyKey)
-	buildImage(imgName,
-		cli.WithFlags("--build-arg", "https_proxy=https://proxy.example.com",
-			"--build-arg", fmt.Sprintf("%s=%s", envKey, envVal),
-			"--build-arg", fmt.Sprintf("%s=%s", explicitProxyKey, explicitProxyVal),
-			"--build-arg", proxy),
-		build.WithDockerfile(dockerfile),
-	).Assert(c, icmd.Success)
 
-	out, _ := dockerCmd(c, "history", "--no-trunc", imgName)
+	buildImage := func(imgName string) string {
+		cli.BuildCmd(c, imgName,
+			cli.WithFlags("--build-arg", "https_proxy=https://proxy.example.com",
+				"--build-arg", fmt.Sprintf("%s=%s", envKey, envVal),
+				"--build-arg", fmt.Sprintf("%s=%s", explicitProxyKey, explicitProxyVal),
+				"--build-arg", proxy),
+			build.WithDockerfile(dockerfile),
+		)
+		return getIDByName(c, imgName)
+	}
+
+	origID := buildImage(imgName)
+	result := cli.DockerCmd(c, "history", "--no-trunc", imgName)
+	out := result.Stdout()
+
 	if strings.Contains(out, proxy) {
 		c.Fatalf("failed to exclude proxy settings from history!")
 	}
@@ -4375,6 +4382,9 @@ func (s *DockerSuite) TestBuildTimeArgHistoryExclusions(c *check.C) {
 	if !strings.Contains(out, fmt.Sprintf("%s=%s", envKey, envVal)) {
 		c.Fatalf("missing build arguments from output")
 	}
+
+	cacheID := buildImage(imgName + "-two")
+	c.Assert(origID, checker.Equals, cacheID)
 }
 
 func (s *DockerSuite) TestBuildBuildTimeArgCacheHit(c *check.C) {