fix: Defer lookup of git in $PATH for git-repo externals

internal/chezmoi/lazy.go

@@ -1,9 +1,23 @@
 package chezmoi
 
+import "os/exec"
+
+// A commandFunc is a function that returns an *os/exec.Cmd.
+type commandFunc func() *exec.Cmd
+
 // A contentsFunc is a function that returns the contents of a file or an error.
 // It is typically used for lazy evaluation of a file's contents.
 type contentsFunc func() ([]byte, error)
 
+// A lazyCommand returns an *os/exec.Cmd lazily. It is needed to defer the call
+// to os/exec.Command because os/exec.Command calls os/exec.LookupPath and
+// therefore depends on the state of $PATH when os/exec.Command is called, not
+// the state of $PATH when os/exec.Cmd.{Run,Start} is called.
+type lazyCommand struct {
+	commandFunc commandFunc
+	command     *exec.Cmd
+}
+
 // A lazyContents evaluates its contents lazily.
 type lazyContents struct {
 	contentsFunc   contentsFunc
@@ -24,6 +38,22 @@ type lazyLinkname struct {
 	linknameSHA256 []byte
 }
 
+// newLazyCommandFunc returns a new lazyCommand with commandFunc.
+func newLazyCommandFunc(commandFunc func() *exec.Cmd) *lazyCommand {
+	return &lazyCommand{
+		commandFunc: commandFunc,
+	}
+}
+
+// Command returns lc's command.
+func (lc *lazyCommand) Command() *exec.Cmd {
+	if lc.commandFunc != nil {
+		lc.command = lc.commandFunc()
+		lc.commandFunc = nil
+	}
+	return lc.command
+}
+
 // newLazyContents returns a new lazyContents with contents.
 func newLazyContents(contents []byte) *lazyContents {
 	return &lazyContents{
@@ -32,7 +62,7 @@ func newLazyContents(contents []byte) *lazyContents {
 }
 
 // newLazyContentsFunc returns a new lazyContents with contentsFunc.
-func newLazyContentsFunc(contentsFunc func() ([]byte, error)) *lazyContents {
+func newLazyContentsFunc(contentsFunc contentsFunc) *lazyContents {
 	return &lazyContents{
 		contentsFunc: contentsFunc,
 	}

internal/chezmoi/sourcestate.go

@@ -1132,15 +1132,17 @@ func (s *SourceState) Read(ctx context.Context, options *ReadOptions) error {
 			switch _, err := s.system.Lstat(destAbsPath); {
 			case errors.Is(err, fs.ErrNotExist):
 				// FIXME add support for using builtin git
-				args := []string{"clone"}
-				args = append(args, external.Clone.Args...)
-				args = append(args, external.URL, destAbsPath.String())
-				cmd := exec.Command("git", args...)
-				cmd.Stdin = os.Stdin
-				cmd.Stdout = os.Stdout
-				cmd.Stderr = os.Stderr
 				sourceStateCommand := &SourceStateCommand{
-					cmd:           cmd,
+					cmd: newLazyCommandFunc(func() *exec.Cmd {
+						args := []string{"clone"}
+						args = append(args, external.Clone.Args...)
+						args = append(args, external.URL, destAbsPath.String())
+						cmd := exec.Command("git", args...)
+						cmd.Stdin = os.Stdin
+						cmd.Stdout = os.Stdout
+						cmd.Stderr = os.Stderr
+						return cmd
+					}),
 					origin:        external,
 					forceRefresh:  options.RefreshExternals == RefreshExternalsAlways,
 					refreshPeriod: external.RefreshPeriod,
@@ -1153,15 +1155,17 @@ func (s *SourceState) Read(ctx context.Context, options *ReadOptions) error {
 				return err
 			default:
 				// FIXME add support for using builtin git
-				args := []string{"pull"}
-				args = append(args, external.Pull.Args...)
-				cmd := exec.Command("git", args...)
-				cmd.Dir = destAbsPath.String()
-				cmd.Stdin = os.Stdin
-				cmd.Stdout = os.Stdout
-				cmd.Stderr = os.Stderr
 				sourceStateCommand := &SourceStateCommand{
-					cmd:           cmd,
+					cmd: newLazyCommandFunc(func() *exec.Cmd {
+						args := []string{"pull"}
+						args = append(args, external.Pull.Args...)
+						cmd := exec.Command("git", args...)
+						cmd.Dir = destAbsPath.String()
+						cmd.Stdin = os.Stdin
+						cmd.Stdout = os.Stdout
+						cmd.Stderr = os.Stderr
+						return cmd
+					}),
 					origin:        external,
 					forceRefresh:  options.RefreshExternals == RefreshExternalsAlways,
 					refreshPeriod: external.RefreshPeriod,

internal/chezmoi/sourcestateentry.go

@@ -2,7 +2,6 @@ package chezmoi
 
 import (
 	"encoding/hex"
-	"os/exec"
 
 	"github.com/rs/zerolog"
 
@@ -38,7 +37,7 @@ type SourceStateEntry interface {
 
 // A SourceStateCommand represents a command that should be run.
 type SourceStateCommand struct {
-	cmd           *exec.Cmd
+	cmd           *lazyCommand
 	origin        SourceStateOrigin
 	forceRefresh  bool
 	refreshPeriod Duration
@@ -96,7 +95,7 @@ func (s *SourceStateCommand) Evaluate() error {
 // MarshalZerologObject implements
 // github.com/rs/zerolog.LogObjectMarshaler.MarshalZerologObject.
 func (s *SourceStateCommand) MarshalZerologObject(e *zerolog.Event) {
-	e.EmbedObject(chezmoilog.OSExecCmdLogObject{Cmd: s.cmd})
+	e.EmbedObject(chezmoilog.OSExecCmdLogObject{Cmd: s.cmd.Command()})
 	e.Str("origin", s.origin.OriginString())
 }
 

internal/chezmoi/targetstateentry.go

@@ -5,7 +5,6 @@ import (
 	"encoding/hex"
 	"fmt"
 	"io/fs"
-	"os/exec"
 	"runtime"
 	"time"
 )
@@ -26,7 +25,7 @@ type TargetStateEntry interface {
 // A TargetStateModifyDirWithCmd represents running a command that modifies
 // a directory.
 type TargetStateModifyDirWithCmd struct {
-	cmd           *exec.Cmd
+	cmd           *lazyCommand
 	forceRefresh  bool
 	refreshPeriod Duration
 	sourceAttr    SourceAttr
@@ -91,7 +90,7 @@ func (t *TargetStateModifyDirWithCmd) Apply(
 	}
 
 	runAt := time.Now().UTC()
-	if err := system.RunCmd(t.cmd); err != nil {
+	if err := system.RunCmd(t.cmd.Command()); err != nil {
 		return false, fmt.Errorf("%s: %w", actualStateEntry.Path(), err)
 	}
 

internal/cmd/testdata/scripts/issue3510.txtar

@@ -0,0 +1,21 @@
+[windows] skip 'UNIX only'
+
+expandenv $CHEZMOISOURCEDIR/.chezmoiexternal.toml
+
+# test that chezmoi apply does not cache the absence of git in $PATH at startup
+exec chezmoi apply
+stdout 'using newly-installed git'
+
+-- golden/git --
+#!/bin/sh
+
+echo "using newly-installed git"
+-- home/user/.local/share/chezmoi/.chezmoiexternal.toml --
+[".dir"]
+    type = "git-repo"
+    url = "file://$WORK/repo"
+-- home/user/.local/share/chezmoi/run_once_before_install-git.sh --
+#!/bin/sh
+
+mkdir -p $WORK/bin
+install -m 755 $WORK/golden/git $WORK/bin