[update] Fix update (#1662)

## Summary

nix 2.19 changed how `nix flake update`
[works](https://nixos.org/manual/nix/stable/release-notes/rl-2.19).

This fixes it. 

## How was it tested?

- [x] Run update on nix < 2.19 and 2.19
- [x] Add update unit test

Author: mikeland73

.github/workflows/cli-tests.yaml

@@ -137,8 +137,8 @@ jobs:
         # Run tests on:
         # 1. the oldest supported nix version (which is 2.9.0? But determinate-systems installer has 2.12.0)
         # 2. nix version 2.17.0 which introduces a new code path that minimizes nixpkgs downloads.
-        # 3. latest nix version (currently, that is 2.17.0, so omitted)
-        nix-version: ["2.12.0", "2.17.0"]
+        # 3. latest nix version
+        nix-version: ["2.12.0", "2.17.0", "2.19.2"]
         exclude:
           - is-main: "not-main"
             os: "${{ inputs.run-mac-tests && 'dummy' || 'macos-latest' }}"
@@ -242,7 +242,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest]
-        nix-version: [2.15.1, 2.16.1, 2.17.0, 2.18.0]
+        nix-version: [2.15.1, 2.16.1, 2.17.0, 2.18.0, 2.19.2]
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v3

internal/nix/upgrade.go

@@ -10,6 +10,7 @@ import (
 
 	"go.jetpack.io/devbox/internal/redact"
 	"go.jetpack.io/devbox/internal/ux"
+	"go.jetpack.io/devbox/internal/vercheck"
 )
 
 func ProfileUpgrade(ProfileDir string, idx int) error {
@@ -28,8 +29,16 @@ func ProfileUpgrade(ProfileDir string, idx int) error {
 }
 
 func FlakeUpdate(ProfileDir string) error {
+	version, err := Version()
+	if err != nil {
+		return err
+	}
 	ux.Finfo(os.Stderr, "Running \"nix flake update\"\n")
-	cmd := exec.Command("nix", "flake", "update", ProfileDir)
+	cmd := exec.Command("nix", "flake", "update")
+	if vercheck.SemverCompare(version, "2.19.0") >= 0 {
+		cmd.Args = append(cmd.Args, "--flake")
+	}
+	cmd.Args = append(cmd.Args, ProfileDir)
 	cmd.Args = append(cmd.Args, ExperimentalFlags()...)
 	out, err := cmd.CombinedOutput()
 	if err != nil {

testscripts/update/update.test.txt

@@ -0,0 +1,36 @@
+# Testscript for exercising devbox update
+
+exec devbox install
+
+exec devbox update
+
+-- devbox.json --
+{
+  "packages": [
+    "hello@latest",
+  ]
+}
+
+-- devbox.lock --
+{
+  "lockfile_version": "1",
+  "packages": {
+    "[email protected]": {
+      "last_modified": "2022-01-26T13:01:16Z",
+      "resolved": "github:NixOS/nixpkgs/e722007bf05802573b41701c49da6c8814878171#hello",
+      "source": "devbox-search",
+      "version": "2.10",
+      "systems": {
+        "aarch64-darwin": {
+          "store_path": "/nix/store/c24460c0iw7kai6z5aan6mkgfclpl2qj-hello-2.10"
+        },
+        "x86_64-darwin": {
+          "store_path": "/nix/store/6wzargj47480y84cqqnm7n30xwqlbyrm-hello-2.10"
+        },
+        "x86_64-linux": {
+          "store_path": "/nix/store/nndmy96lswhxc4xp49n950i1905qlfpy-hello-2.10"
+        }
+      }
+    }
+  }
+}