command/plan: user friendly error if plan file given to plan command

command/plan.go

@@ -61,7 +61,7 @@ func (c *PlanCommand) Run(args []string) int {
 	// This is going to keep track of shadow errors
 	var shadowErr error
 
-	ctx, _, err := c.Context(contextOpts{
+	ctx, planned, err := c.Context(contextOpts{
 		Destroy:     destroy,
 		Path:        path,
 		StatePath:   c.Meta.statePath,
@@ -71,6 +71,13 @@ func (c *PlanCommand) Run(args []string) int {
 		c.Ui.Error(err.Error())
 		return 1
 	}
+	if planned {
+		c.Ui.Error(
+			"The plan command cannot be called with a saved plan file.\n\n" +
+				"The plan command expects a configuration directory as an argument.",
+		)
+		return 1
+	}
 
 	err = terraform.SetDebugInfo(DefaultDataDir)
 	if err != nil {

command/plan_test.go

@@ -37,6 +37,29 @@ func TestPlan(t *testing.T) {
 	}
 }
 
+func TestPlan_plan(t *testing.T) {
+	tmp, cwd := testCwd(t)
+	defer testFixCwd(t, tmp, cwd)
+
+	planPath := testPlanFile(t, &terraform.Plan{
+		Module: testModule(t, "apply"),
+	})
+
+	p := testProvider()
+	ui := new(cli.MockUi)
+	c := &PlanCommand{
+		Meta: Meta{
+			ContextOpts: testCtxConfig(p),
+			Ui:          ui,
+		},
+	}
+
+	args := []string{planPath}
+	if code := c.Run(args); code != 1 {
+		t.Fatalf("bad: %d\n\n%s", code, ui.ErrorWriter.String())
+	}
+}
+
 func TestPlan_destroy(t *testing.T) {
 	originalState := &terraform.State{
 		Modules: []*terraform.ModuleState{