cmd/cue: don't use os.Getwd at init time

Users of the Go API at ./cmd/cue/cmd may wish to use os.Chdir
before executing the CUE CLI, which is perfectly reasonable.

That worked until https://cuelang.org/cl/1195084, where we started
deduplicating calls to os.Getwd, but we did not think about
the Go API users and os.Chdir.

Instead, use a sync.OnceValue so that the first need for a working
directory does call os.Getwd, and the value is kept from that point.

Note that, to properly support os.Chdir calls between cmd.New calls,
the global variable is re-initialized by New.

Fixes #3916.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I2b40c5238b351b5feee441fde065b73af3ef2919
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1214672
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Roger Peppe <[email protected]>

Author: mvdan

cmd/cue/cmd/cmd.go

@@ -147,7 +147,7 @@ Run "cue help commands" for more details on tasks and workflow commands.
 			sub, err := customCommand(cmd, commandSection, args[0], tools)
 			if err != nil {
 				w := cmd.OutOrStderr()
-				fmt.Fprint(w, errors.Details(err, &errors.Config{Cwd: rootWorkingDir}))
+				fmt.Fprint(w, errors.Details(err, &errors.Config{Cwd: rootWorkingDir()}))
 				fmt.Fprintln(w, `Ensure custom commands are defined in a "_tool.cue" file.`)
 				fmt.Fprintln(w, "Run 'cue help cmd' to list available custom commands.")
 				return ErrPrintedError

cmd/cue/cmd/fix.go

@@ -57,7 +57,7 @@ func runFixAll(cmd *Command, args []string) error {
 	if len(args) == 0 {
 		args = []string{"./..."}
 
-		dir := rootWorkingDir
+		dir := rootWorkingDir()
 		for {
 			if _, err := os.Stat(filepath.Join(dir, "cue.mod")); err == nil {
 				args = appendDirs(args, filepath.Join(dir, "cue.mod", "gen"))

cmd/cue/cmd/fmt.go

@@ -205,7 +205,7 @@ func formatFile(file *build.File, opts []format.Option, doDiff, check bool, cmd
 		return false, nil
 	}
 
-	path, err := filepath.Rel(rootWorkingDir, file.Filename)
+	path, err := filepath.Rel(rootWorkingDir(), file.Filename)
 	if err != nil {
 		path = file.Filename
 	}

cmd/cue/cmd/import.go

@@ -479,7 +479,7 @@ func handleFile(b *buildPlan, f *ast.File) (err error) {
 
 func writeFile(p *buildPlan, f *ast.File, cueFile string) error {
 	if flagDryRun.Bool(p.cmd) {
-		cueFile, err := filepath.Rel(rootWorkingDir, cueFile)
+		cueFile, err := filepath.Rel(rootWorkingDir(), cueFile)
 		if err != nil {
 			return err
 		}

cmd/cue/cmd/modget.go

@@ -118,7 +118,7 @@ func readModuleFile() (string, *modfile.File, []byte, error) {
 func findModuleRoot() (string, error) {
 	// TODO this logic is duplicated in multiple places. We should
 	// consider deduplicating it.
-	dir := rootWorkingDir
+	dir := rootWorkingDir()
 	for {
 		if _, err := os.Stat(filepath.Join(dir, "cue.mod")); err == nil {
 			return dir, nil

cmd/cue/cmd/modinit.go

@@ -58,7 +58,7 @@ func runModInit(cmd *Command, args []string) (err error) {
 		}
 	}
 
-	mod := filepath.Join(rootWorkingDir, "cue.mod")
+	mod := filepath.Join(rootWorkingDir(), "cue.mod")
 	if info, err := os.Stat(mod); err == nil {
 		if !info.IsDir() {
 			return fmt.Errorf("cue.mod files are no longer supported; use cue.mod/module.cue")

cmd/cue/cmd/modpublish.go

@@ -308,7 +308,7 @@ func rootLICENSEFile(ctx context.Context, vcsImpl vcs.VCS) (string, error) {
 
 	// relLicenseFile is used in a couple of error situations below
 	relLicenseFile := func() string {
-		rel, err := filepath.Rel(rootWorkingDir, licenseFile)
+		rel, err := filepath.Rel(rootWorkingDir(), licenseFile)
 		if err == nil {
 			return rel
 		}

cmd/cue/cmd/root.go

@@ -22,6 +22,7 @@ import (
 	"os"
 	"runtime"
 	"runtime/pprof"
+	"sync"
 	"testing"
 	"time"
 
@@ -201,13 +202,28 @@ func mkRunE(c *Command, f runFunction) func(*cobra.Command, []string) error {
 	}
 }
 
+// rootWorkingDir avoids repeated calls to [os.Getwd] in cmd/cue.
+// If we can't figure out the current directory, something is very wrong,
+// and there's no point in continuing to run a command.
+var rootWorkingDir = func() string { panic("must be replaced by a sync.OnceValue") }
+
 // TODO(mvdan): remove this error return at some point.
 // The API could also be made clearer if we want to keep cmd public,
 // such as not leaking *cobra.Command via embedding.
 
 // New creates the top-level command.
 // The returned error is always nil, and is a historical artifact.
 func New(args []string) (*Command, error) {
+	// Each call to New resets rootWorkingDir, to support [os.Chdir] calls in between.
+	rootWorkingDir = sync.OnceValue(func() string {
+		wd, err := os.Getwd()
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "cannot get current directory: %v\n", err)
+			os.Exit(1)
+		}
+		return wd
+	})
+
 	cmd := &cobra.Command{
 		Use: "cue",
 		// TODO: the short help text below seems to refer to `cue cmd`, like helpTemplate.
@@ -273,18 +289,6 @@ func New(args []string) (*Command, error) {
 	return c, nil
 }
 
-// rootWorkingDir avoids repeated calls to [os.Getwd] in cmd/cue.
-// If we can't figure out the current directory, something is very wrong,
-// and there's no point in continuing to run a command.
-var rootWorkingDir = func() string {
-	wd, err := os.Getwd()
-	if err != nil {
-		fmt.Fprintf(os.Stderr, "cannot get current directory: %v\n", err)
-		os.Exit(1)
-	}
-	return wd
-}()
-
 // Main runs the cue tool and returns the code for passing to os.Exit.
 func Main() int {
 	start := time.Now()
@@ -302,7 +306,7 @@ func Main() int {
 	if err := cmd.Run(backgroundContext()); err != nil {
 		if err != ErrPrintedError {
 			errors.Print(os.Stderr, err, &errors.Config{
-				Cwd:     rootWorkingDir,
+				Cwd:     rootWorkingDir(),
 				ToSlash: testing.Testing(),
 			})
 		}
@@ -389,7 +393,7 @@ func printError(cmd *Command, err error) {
 	}
 	errors.Print(cmd.Stderr(), err, &errors.Config{
 		Format:  format,
-		Cwd:     rootWorkingDir,
+		Cwd:     rootWorkingDir(),
 		ToSlash: testing.Testing(),
 	})
 }

cmd/cue/cmd/root_test.go

@@ -18,6 +18,7 @@ import (
 	"bytes"
 	"context"
 	"io"
+	"os"
 	"strings"
 	"testing"
 
@@ -60,4 +61,31 @@ func TestCommand(t *testing.T) {
 	qt.Assert(t, qt.IsNil(err))
 	err = c.Execute()
 	qt.Assert(t, qt.IsNotNil(err))
+
+	// Verify that we can change the current directory via [os.Chdir].
+	// We test by ensuring we can load the module under testdata/files,
+	// which uses the working directory as a starting point to find a module root.
+	t.Run("Chdir", func(t *testing.T) {
+		// TODO: use [testing.T.Chdir] once we can use Go 1.24 or later.
+		origDir, err := os.Getwd()
+		qt.Assert(t, qt.IsNil(err))
+
+		qt.Assert(t, qt.IsNil(os.Chdir("testdata/module_broken")))
+		t.Cleanup(func() {
+			qt.Assert(t, qt.IsNil(os.Chdir(origDir)))
+		})
+
+		c, err = cmd.New([]string{"mod", "tidy", "--check"})
+		qt.Assert(t, qt.IsNil(err))
+		err = c.Execute()
+		qt.Assert(t, qt.ErrorMatches(err, `^disallowed: field not allowed`))
+
+		// Change the directory a second time, to ensure the global state is not sticky.
+		qt.Assert(t, qt.IsNil(os.Chdir("../module_ok")))
+
+		c, err = cmd.New([]string{"mod", "tidy", "--check"})
+		qt.Assert(t, qt.IsNil(err))
+		err = c.Execute()
+		qt.Assert(t, qt.IsNil(err))
+	})
 }

cmd/cue/cmd/testdata/module_broken/cue.mod/module.cue

@@ -0,0 +1,5 @@
+// As used by TestCommand/Chdir.
+
+module: "broken.test/root"
+language: version: "v0.13.0"
+disallowed: "should fail mod tidy"