Added msys2/cygwin terminal detection support

log/term/terminal_windows.go

@@ -8,24 +8,77 @@
 package term
 
 import (
+	"encoding/binary"
 	"io"
+	"regexp"
 	"syscall"
 	"unsafe"
 )
 
 var kernel32 = syscall.NewLazyDLL("kernel32.dll")
 
 var (
-	procGetConsoleMode = kernel32.NewProc("GetConsoleMode")
+	procGetFileInformationByHandleEx = kernel32.NewProc("GetFileInformationByHandleEx")
+	msysPipeNameRegex                = regexp.MustCompile(`\\(cygwin|msys)-\w+-pty\d?-(to|from)-master`)
+)
+
+const (
+	fileNameInfo = 0x02
 )
 
 // IsTerminal returns true if w writes to a terminal.
 func IsTerminal(w io.Writer) bool {
-	fw, ok := w.(fder)
-	if !ok {
+	var handle syscall.Handle
+
+	if fw, ok := w.(fder); ok {
+		handle = syscall.Handle(fw.Fd())
+	} else {
+		// The writer has no file-descriptor and so can't be a terminal.
 		return false
 	}
+
 	var st uint32
-	r, _, e := syscall.Syscall(procGetConsoleMode.Addr(), 2, fw.Fd(), uintptr(unsafe.Pointer(&st)), 0)
-	return r != 0 && e == 0
+
+	// If the terminal is a Windows console, succeed right away.
+	if err := syscall.GetConsoleMode(handle, &st); err == nil && st != 0 {
+		return true
+	}
+
+	// The terminal is not a cmd.exe terminal, let's try to detect MSYS2 terminals.
+	filetype, err := syscall.GetFileType(handle)
+
+	// MSYS2 terminal reports as a pipe.
+	if filetype != syscall.FILE_TYPE_PIPE || err != nil {
+		return false
+	}
+
+	// MSYS2/Cygwin terminal's name looks like: \msys-dd50a72ab4668b33-pty2-to-master
+	data := make([]byte, 256, 256)
+
+	r, _, e := syscall.Syscall6(
+		procGetFileInformationByHandleEx.Addr(),
+		4,
+		uintptr(handle),
+		uintptr(fileNameInfo),
+		uintptr(unsafe.Pointer(&data[0])),
+		uintptr(len(data)),
+		0,
+		0,
+	)
+
+	if r != 0 && e == 0 {
+		// The first 4 bytes of the buffer are the size of the UTF16 name, in bytes.
+		unameLen := binary.LittleEndian.Uint32(data[:4]) / 2
+		uname := make([]uint16, unameLen, unameLen)
+
+		for i := uint32(0); i < unameLen; i++ {
+			uname[i] = binary.LittleEndian.Uint16(data[i*2+4 : i*2+2+4])
+		}
+
+		name := syscall.UTF16ToString(uname)
+
+		return msysPipeNameRegex.MatchString(name)
+	}
+
+	return false
 }

log/term/terminal_windows_test.go

@@ -0,0 +1,56 @@
+package term
+
+import (
+	"fmt"
+	"syscall"
+	"testing"
+)
+
+// +build windows
+
+type myWriter struct {
+	fd uintptr
+}
+
+func (w *myWriter) Write(p []byte) (int, error) {
+	return 0, fmt.Errorf("not implemented")
+}
+
+func (w *myWriter) Fd() uintptr {
+	return w.fd
+}
+
+var procGetStdHandle = kernel32.NewProc("GetStdHandle")
+
+const stdOutputHandle = ^uintptr(0) - 11 + 1
+
+func getConsoleHandle() syscall.Handle {
+	ptr, err := syscall.UTF16PtrFromString("CONOUT$")
+
+	if err != nil {
+		panic(err)
+	}
+
+	handle, err := syscall.CreateFile(ptr, syscall.GENERIC_READ|syscall.GENERIC_WRITE, syscall.FILE_SHARE_READ, nil, syscall.OPEN_EXISTING, 0, 0)
+
+	if err != nil {
+		panic(err)
+	}
+
+	return handle
+}
+
+func TestIsTerminal(t *testing.T) {
+	// This is necessary because depending on whether `go test` is called with
+	// the `-v` option, stdout will or will not be bound, changing the behavior
+	// of the test. So we refer to it directly to avoid flakyness.
+	handle := getConsoleHandle()
+
+	writer := &myWriter{
+		fd: uintptr(handle),
+	}
+
+	if !IsTerminal(writer) {
+		t.Errorf("output is supposed to be a terminal")
+	}
+}