feat: Add plugin support

assets/chezmoi.io/docs/reference/plugins.md

@@ -0,0 +1,8 @@
+# Plugins
+
+chezmoi supports plugins, similar to git.
+
+If you run `chezmoi command` where *command* is not a builtin chezmoi command
+then chezmoi will look for a binary called `chezmoi-command` in your `$PATH`. If
+such a binary is found then chezmoi will execute it. Otherwise, chezmoi will
+report an unknown command error.

assets/chezmoi.io/mkdocs.yml

@@ -305,6 +305,7 @@ nav:
       - reference/templates/secret-functions/index.md
       - secret: reference/templates/secret-functions/secret.md
       - secretJSON: reference/templates/secret-functions/secretJSON.md
+  - Plugins: reference/plugins.md
   - Release history: reference/release-history.md
 - Developer:
   - Developing locally: developer/developing-locally.md

internal/cmd/cmd.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"os/exec"
 	"regexp"
 	"runtime/debug"
 	"strconv"
@@ -105,7 +106,18 @@ func (v VersionInfo) MarshalZerologObject(e *zerolog.Event) {
 
 // Main runs chezmoi and returns an exit code.
 func Main(versionInfo VersionInfo, args []string) int {
-	if err := runMain(versionInfo, args); err != nil {
+	err := runMain(versionInfo, args)
+	if err != nil && strings.Contains(err.Error(), "unknown command") &&
+		len(args) > 0 { // FIXME find a better way of detecting unknown commands
+		if name, err2 := exec.LookPath("chezmoi-" + args[0]); err2 == nil {
+			cmd := exec.Command(name, args[1:]...)
+			cmd.Stdin = os.Stdin
+			cmd.Stdout = os.Stdout
+			cmd.Stderr = os.Stderr
+			err = cmd.Run()
+		}
+	}
+	if err != nil {
 		var errExitCode chezmoi.ExitCodeError
 		if errors.As(err, &errExitCode) {
 			return int(errExitCode)

internal/cmd/testdata/scripts/plugin.txtar

@@ -0,0 +1,16 @@
+[unix] chmod 755 bin/chezmoi-plugin
+
+# test that chezmoi returns unknown command errors for unknown commands
+! exec chezmoi unknown
+stderr 'unknown command'
+
+# test that chezmoi executes plugins
+exec chezmoi plugin
+stdout hello
+
+-- bin/chezmoi-plugin --
+#!/bin/sh
+
+echo hello
+-- bin/chezmoi-plugin.cmd --
+@echo hello