[cloud shell] respect gitignore file in --config directory to limit large data syncs (#387)

## Summary

I discovered that the rust-stable project was not syncing, because it
stores compiled
artifacts in a child-directory: `.rustup`. This directory is in the
`.gitignore` file
but mutagen was syncing it.

In the long run, we should not sync any files that are gitignored
(agree?).
However, code for that is a bit more involved, so as a first pass I
implement
looking for a .gitignore file in the `configDir` and passing its rules
to mutagen
as `--ignore` flags. Thankfully, mutagen's ignore rules match gitignore
format.

## How was it tested?

was able to start `devbox cloud shell` in the `rust-stable` example
project

Author: savil

internal/cloud/cloud.go

@@ -14,6 +14,7 @@ import (
 
 	"github.com/AlecAivazis/survey/v2"
 	"github.com/fatih/color"
+	"github.com/pkg/errors"
 	"go.jetpack.io/devbox/internal/cloud/mutagen"
 	"go.jetpack.io/devbox/internal/cloud/mutagenbox"
 	"go.jetpack.io/devbox/internal/cloud/openssh"
@@ -137,6 +138,11 @@ func syncFiles(username, hostname, configDir string) error {
 		return err
 	}
 
+	ignorePaths, err := gitIgnorePaths(configDir)
+	if err != nil {
+		return err
+	}
+
 	// TODO: instead of id, have the server return the machine's name and use that
 	// here to. It'll make things easier to debug.
 	machineID, _, _ := strings.Cut(hostname, ".")
@@ -150,11 +156,14 @@ func syncFiles(username, hostname, configDir string) error {
 		// the projects files. If we pick a pre-existing directories with other files, those
 		// files will be synced back to the local directory (due to two-way-sync) and pollute
 		// the user's local project
-		BetaPath:  fmt.Sprintf("~/code/%s", projectName),
-		EnvVars:   env,
-		IgnoreVCS: true,
-		SyncMode:  "two-way-resolved",
-		Labels:    mutagenbox.DefaultSyncLabels(machineID),
+		BetaPath: fmt.Sprintf("~/code/%s", projectName),
+		EnvVars:  env,
+		Ignore: mutagen.SessionIgnore{
+			VCS:   true,
+			Paths: ignorePaths,
+		},
+		SyncMode: "two-way-resolved",
+		Labels:   mutagenbox.DefaultSyncLabels(machineID),
 	})
 	if err != nil {
 		return err
@@ -202,3 +211,29 @@ func parseVMEnvVar() (username string, vmHostname string) {
 	vmHostname = parts[1]
 	return
 }
+
+// Proof of concept: look for a gitignore file in the current directory.
+// To harden this, we must:
+//  1. Look for .gitignore file in each ancestor directory of configDir, and include
+//     any rules that apply to configDir contents.
+//  2. Look for .gitignore file in each child directory of configDir and transform the
+//     rules to be relative to configDir.
+func gitIgnorePaths(configDir string) ([]string, error) {
+
+	fpath := filepath.Join(configDir, ".gitignore")
+	if _, err := os.Stat(fpath); err != nil {
+		if os.IsNotExist(err) {
+			return nil, nil
+		} else {
+			return nil, errors.WithStack(err)
+		}
+	}
+
+	contents, err := os.ReadFile(fpath)
+	if err != nil {
+		return nil, errors.WithStack(err)
+	}
+
+	result := strings.Split(string(contents), "\n")
+	return result, nil
+}

internal/cloud/mutagen/types.go

@@ -5,6 +5,11 @@ import (
 	"strings"
 )
 
+type SessionIgnore struct {
+	VCS   bool
+	Paths []string
+}
+
 type SessionSpec struct {
 	AlphaAddress string
 	AlphaPath    string
@@ -14,7 +19,7 @@ type SessionSpec struct {
 	Labels       map[string]string
 	Paused       bool
 	SyncMode     string
-	IgnoreVCS    bool
+	Ignore       SessionIgnore
 	EnvVars      map[string]string
 }
 

internal/cloud/mutagen/wrapper.go

@@ -45,10 +45,16 @@ func Create(spec *SessionSpec) error {
 		args = append(args, "--sync-mode", spec.SyncMode)
 	}
 
-	if spec.IgnoreVCS {
+	if spec.Ignore.VCS {
 		args = append(args, "--ignore-vcs")
 	}
 
+	if len(spec.Ignore.Paths) > 0 {
+		for _, p := range spec.Ignore.Paths {
+			args = append(args, "--ignore", p)
+		}
+	}
+
 	return execMutagen(args, spec.EnvVars)
 }