Turn off auto-detection for language on devbox shell (#222)

## Summary
Turn off auto-detection for language on devbox shell. This means:
1. `devbox plan` outputs plan for build only
2. `devbox shell` does not automatically add packages based on the
project
3. `devbox shell` no longer automatically sets init hooks (python can
potentially be the biggest one being affected by this change, but as far
as I know, it wasn't being used before)

I also added a `devbox.json` to the root of this project, because I need
go 1.19 and I have go 1.18 on my personal machine.

## How was it tested?
devbox shell
devbox build
go test ./...

Author: LucilleH

boxcli/plan.go

@@ -31,7 +31,7 @@ func runPlanCmd(cmd *cobra.Command, args []string) error {
 		return errors.WithStack(err)
 	}
 
-	plan, err := box.ShellPlan()
+	plan, err := box.BuildPlan()
 	if err != nil {
 		return errors.WithStack(err)
 	}

devbox.go

@@ -137,13 +137,9 @@ func (d *Devbox) Build(flags *docker.BuildFlags) error {
 
 // Plan creates a plan of the actions that devbox will take to generate its
 // shell environment.
-func (d *Devbox) ShellPlan() (*plansdk.Plan, error) {
-	userPlan := d.convertToPlan()
-	shellPlan, err := planner.GetShellPlan(d.srcDir)
-	if err != nil {
-		return nil, err
-	}
-	return plansdk.MergeUserPlan(userPlan, shellPlan)
+func (d *Devbox) ShellPlan() *plansdk.Plan {
+	// TODO: Move shell plan to a separate struct from build plan.
+	return d.convertToPlan()
 }
 
 // Plan creates a plan of the actions that devbox will take to generate its
@@ -172,24 +168,17 @@ func (d *Devbox) Generate() error {
 // Shell generates the devbox environment and launches nix-shell as a child
 // process.
 func (d *Devbox) Shell() error {
-
 	if err := d.ensurePackagesAreInstalled(install); err != nil {
 		return err
 	}
 
-	plan, err := d.ShellPlan()
-	if err != nil {
-		return errors.WithStack(err)
-	}
-
 	profileDir, err := d.profileDir()
 	if err != nil {
 		return err
 	}
 
 	nixShellFilePath := filepath.Join(d.srcDir, ".devbox/gen/shell.nix")
 	sh, err := nix.DetectShell(
-		nix.WithPlanInitHook(plan.ShellInitHook),
 		nix.WithProfile(profileDir),
 		nix.WithHistoryFile(filepath.Join(d.srcDir, shellHistoryFile)),
 	)
@@ -245,14 +234,7 @@ func (d *Devbox) convertToPlan() *plansdk.Plan {
 }
 
 func (d *Devbox) generateShellFiles() error {
-	shellPlan, err := d.ShellPlan()
-	if err != nil {
-		return errors.WithStack(err)
-	}
-	if shellPlan.Invalid() {
-		return shellPlan.Error()
-	}
-	return generate(d.srcDir, shellPlan, shellFiles)
+	return generate(d.srcDir, d.ShellPlan(), shellFiles)
 }
 
 func (d *Devbox) generateBuildFiles() error {

devbox.json

@@ -0,0 +1,8 @@
+{
+  "packages": [
+    "go_1_19"
+  ],
+  "shell": {
+    "init_hook": null
+  }
+}

devbox_test.go

@@ -48,15 +48,18 @@ func testExample(t *testing.T, testPath string) {
 		box.srcDir, err = filepath.Rel(currentDir, box.srcDir)
 		assert.NoErrorf(err, "expect to construct relative path from %s relative to base %s", box.srcDir, currentDir)
 
-		plan, err := box.ShellPlan()
+		plan, err := box.BuildPlan()
+		buildErrorExpectedFile := filepath.Join(baseDir, "build_error_expected")
+		hasBuildErrorExpectedFile := fileExists(buildErrorExpectedFile)
+		if hasBuildErrorExpectedFile {
+			assert.NotNil(err)
+			// Since build error is expected, skip the rest of the test
+			return
+		}
 		assert.NoError(err, "devbox plan should not fail")
 
-		generateErrorFile := filepath.Join(baseDir, "has_generate_error")
-		hasGenerateErrorFile := fileExists(generateErrorFile)
 		err = box.Generate()
-		if !hasGenerateErrorFile {
-			assert.NoError(err, "devbox generate should not fail")
-		}
+		assert.NoError(err, "devbox generate should not fail")
 
 		if !hasGoldenFile {
 			assert.NotEmpty(plan.DevPackages, "the plan should have dev packages")