fix: 3rd party Windows terminals double encoding win32-input-mode breaks some keys

gdamore · gdamore · commit 0b5424d92c58 · 2025-11-29T13:01:59.000-08:00
The encoding for things like SS3 sequences used in terminals like WezTerm and Alacritty
breaks the processor, since the CSI state machine changes interferes with the SS3
state.  We introduce a nested state machine for this case.

Note that ConEmu still seems busted when running locally, although it is interesting
that using it from an SSH hosted session works well.  Nonetheless, we don't recommend
ConEmu for a variety of reasons.
diff --git a/input.go b/input.go
@@ -80,14 +80,18 @@ type inputProcessor struct {
 	timer     *time.Timer
 	expire    time.Time
 	l         sync.Mutex
-	reencode  bool // bug with win32-input-mode on older terms
 	encBuf    []rune
 	evch      chan<- Event
 	rows      int // used for clipping mouse coordinates
 	cols      int // used for clipping mouse coordinates
+	nested    *inputProcessor
 }
 
 func (ip *inputProcessor) SetSize(w, h int) {
+	if ip.nested != nil {
+		ip.nested.SetSize(w, h)
+		return
+	}
 	go func() {
 		ip.l.Lock()
 		ip.rows = h
@@ -401,7 +405,7 @@ func (ip *inputProcessor) scan() {
 			case '\x1b':
 				// escape.. pending
 				ip.state = inpStateEsc
-				if len(ip.buf) == 0 {
+				if len(ip.buf) == 0 && ip.nested == nil {
 					ip.expire = time.Now().Add(time.Millisecond * 50)
 					ip.timer = time.AfterFunc(time.Millisecond*60, ip.escTimeout)
 				}
@@ -671,21 +675,16 @@ func (ip *inputProcessor) handleWinKey(P []int) {
 		// key up event ignore ignore
 		return
 	}
-	if P[0] == 0 {
-		if P[2] == 27 && !ip.reencode {
-			ip.reencode = true
+	if P[0] == 0 && P[2] == 27 && ip.nested == nil {
+		ip.nested = &inputProcessor{
+			evch: ip.evch,
+			rows: ip.rows,
+			cols: ip.cols,
 		}
 	}
-	if ip.reencode {
-		ip.encBuf = append(ip.encBuf, rune(P[2]))
-		// embedded content will itself be a CSI, so terminated by a CSI terminator
-		if len(ip.encBuf) > 2 && P[2] >= 0x40 && P[2] < 0x7F {
-			eb := ip.encBuf
-			ip.encBuf = nil
-			ip.reencode = false
-			ip.buf = append(eb, ip.buf...)
-			go ip.ScanUTF8(nil)
-		}
+
+	if ip.nested != nil && P[2] > 0 && P[2] < 0x80 { // only ASCII in win32-input-mode
+		ip.nested.ScanUTF8([]byte{byte(P[2])})
 		return
 	}
 
@@ -814,7 +813,7 @@ func (ip *inputProcessor) handleCsi(mode rune, params []byte, intermediate []byt
 				ip.post(NewEventKey(ks.Key, 0, mod))
 				return
 			}
-			if P0 == 27 && len(P) > 2 {
+			if P0 == 27 && len(P) > 2 && P[2] > 0 && P[2] <= 0xff {
 				if P[2] < ' ' || P[2] == 0x7F {
 					ip.post(NewEventKey(Key(P[2]), 0, mod))
 				} else {
diff --git a/tscreen.go b/tscreen.go
@@ -24,6 +24,7 @@ import (
 	"io"
 	"maps"
 	"os"
+	"runtime"
 	"strconv"
 	"strings"
 	"sync"
@@ -319,12 +320,22 @@ func (t *tScreen) prepareExtendedOSC() {
 	}
 
 	if t.enableCsiU == "" && t.ti.XTermLike {
-		// three advanced keyboard protocols:
-		// - xterm modifyOtherKeys (uses CSI 27 ~ )
-		// - kitty csi-u (uses CSI u)
-		// - win32-input-mode (uses CSI _)
-		t.enableCsiU = "\x1b[>4;2m" + "\x1b[>1u" + "\x1b[9001h"
-		t.disableCsiU = "\x1b[9001l" + "\x1b[<u" + "\x1b[>4;0m"
+		if runtime.GOOS == "windows" && (os.Getenv("TERM") == "" || os.Getenv("TERM_PROGRAM") == "WezTerm") {
+			// on Windows, if we don't have a TERM, use only win32-input-mode
+			t.enableCsiU = "\x1b[?9001h"
+			t.disableCsiU = "\x1b[?9001l"
+		} else if os.Getenv("TERM_PROGRAM") == "WezTerm" {
+			// WezTerm is unhappy if we ask for other modes
+			t.enableCsiU = "\x1b[>1u"
+			t.disableCsiU = "\x1b[<u"
+		} else {
+			// three advanced keyboard protocols:
+			// - xterm modifyOtherKeys (uses CSI 27 ~ )
+			// - kitty csi-u (uses CSI u)
+			// - win32-input-mode (uses CSI _)
+			t.enableCsiU = "\x1b[>4;2m" + "\x1b[>1u" + "\x1b[9001h"
+			t.disableCsiU = "\x1b[9001l" + "\x1b[<u" + "\x1b[>4;0m"
+		}
 	}
 }
 
