Use winpty to launch fzf in Git bash (mintty)

Close #3806

Known limitation:
* --height cannot be used

src/proxy.go

@@ -0,0 +1,132 @@
+package fzf
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"github.com/junegunn/fzf/src/tui"
+	"github.com/junegunn/fzf/src/util"
+)
+
+const becomeSuffix = ".become"
+
+func escapeSingleQuote(str string) string {
+	return "'" + strings.ReplaceAll(str, "'", "'\\''") + "'"
+}
+
+func fifo(name string) (string, error) {
+	ns := time.Now().UnixNano()
+	output := filepath.Join(os.TempDir(), fmt.Sprintf("fzf-%s-%d", name, ns))
+	output, err := mkfifo(output, 0600)
+	if err != nil {
+		return output, err
+	}
+	return output, nil
+}
+
+func runProxy(commandPrefix string, cmdBuilder func(temp string) *exec.Cmd, opts *Options, withExports bool) (int, error) {
+	output, err := fifo("proxy-output")
+	if err != nil {
+		return ExitError, err
+	}
+	defer os.Remove(output)
+
+	// Take the output
+	go func() {
+		withOutputPipe(output, func(outputFile io.ReadCloser) {
+			if opts.Output == nil {
+				io.Copy(os.Stdout, outputFile)
+			} else {
+				reader := bufio.NewReader(outputFile)
+				sep := opts.PrintSep[0]
+				for {
+					item, err := reader.ReadString(sep)
+					if err != nil {
+						break
+					}
+					opts.Output <- item
+				}
+			}
+		})
+	}()
+
+	var command string
+	commandPrefix += ` --proxy-script "$0"`
+	if opts.Input == nil && util.IsTty() {
+		command = fmt.Sprintf(`%s > %q`, commandPrefix, output)
+	} else {
+		input, err := fifo("proxy-input")
+		if err != nil {
+			return ExitError, err
+		}
+		defer os.Remove(input)
+
+		go func() {
+			withInputPipe(input, func(inputFile io.WriteCloser) {
+				if opts.Input == nil {
+					io.Copy(inputFile, os.Stdin)
+				} else {
+					for item := range opts.Input {
+						fmt.Fprint(inputFile, item+opts.PrintSep)
+					}
+				}
+			})
+		}()
+
+		if withExports {
+			command = fmt.Sprintf(`%s < %q > %q`, commandPrefix, input, output)
+		} else {
+			// For mintty: cannot directly read named pipe from Go code
+			command = fmt.Sprintf(`command cat %q | %s > %q`, input, commandPrefix, output)
+		}
+	}
+
+	// To ensure that the options are processed by a POSIX-compliant shell,
+	// we need to write the command to a temporary file and execute it with sh.
+	var exports []string
+	if withExports {
+		exports = os.Environ()
+		for idx, pairStr := range exports {
+			pair := strings.SplitN(pairStr, "=", 2)
+			exports[idx] = fmt.Sprintf("export %s=%s", pair[0], escapeSingleQuote(pair[1]))
+		}
+	}
+	temp := writeTemporaryFile(append(exports, command), "\n")
+	defer os.Remove(temp)
+
+	cmd := cmdBuilder(temp)
+	if err := cmd.Run(); err != nil {
+		if exitError, ok := err.(*exec.ExitError); ok {
+			code := exitError.ExitCode()
+			if code == ExitBecome {
+				becomeFile := temp + becomeSuffix
+				data, err := os.ReadFile(becomeFile)
+				os.Remove(becomeFile)
+				if err != nil {
+					return ExitError, err
+				}
+				elems := strings.Split(string(data), "\x00")
+				if len(elems) < 1 {
+					return ExitError, errors.New("invalid become command")
+				}
+				command := elems[0]
+				env := []string{}
+				if len(elems) > 1 {
+					env = elems[1:]
+				}
+				executor := util.NewExecutor(opts.WithShell)
+				executor.Become(tui.TtyIn(), env, command)
+			}
+			return code, err
+		}
+	}
+
+	return ExitOk, nil
+}