From d5a80357237612da52e2e50a760c3d95f67b17bf Mon Sep 17 00:00:00 2001
From: Marijn Haverbeke <marijn@haverbeke.berlin>
Date: Fri, 1 Dec 2023 12:46:24 +0100
Subject: [PATCH] Fix cursor motion loop on misplaced zero-width non-joiner

FIX: Fix an issue in the bidirectional motion that could cause the cursor to get stuck
in a loop when a zero-width non-joiner char was placed on a direction boundary.

Closes https://github.com/codemirror/dev/issues/1302
---
 src/bidi.ts          |  7 +++----
 test/webtest-bidi.ts | 17 ++++++++++++++++-
 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/src/bidi.ts b/src/bidi.ts
index 2167b6f..82ea8c3 100644
--- a/src/bidi.ts
+++ b/src/bidi.ts
@@ -62,9 +62,8 @@ function charType(ch: number) {
     0x590 <= ch && ch <= 0x5f4 ? T.R :
     0x600 <= ch && ch <= 0x6f9 ? ArabicTypes[ch - 0x600] :
     0x6ee <= ch && ch <= 0x8ac ? T.AL :
-    0x2000 <= ch && ch <= 0x200b ? T.NI :
-    0xfb50 <= ch && ch <= 0xfdff ? T.AL :
-    ch == 0x200c ? T.NI : T.L
+    0x2000 <= ch && ch <= 0x200c ? T.NI :
+    0xfb50 <= ch && ch <= 0xfdff ? T.AL : T.L
 }
 
 const BidiRE = /[\u0590-\u05f4\u0600-\u06ff\u0700-\u08ac\ufb50-\ufdff]/
@@ -436,7 +435,7 @@ export function moveVisually(line: Line, order: readonly BidiSpan[], dir: Direct
   let nextIndex = findClusterBreak(line.text, startIndex, indexForward)
   movedOver = line.text.slice(Math.min(startIndex, nextIndex), Math.max(startIndex, nextIndex))
 
-  if (nextIndex != span.side(forward, dir))
+  if (nextIndex > span.from && nextIndex < span.to)
     return EditorSelection.cursor(nextIndex + line.from, indexForward ? -1 : 1, span.level)
   let nextSpan = spanI == (forward ? order.length - 1 : 0) ? null : order[spanI + (forward ? 1 : -1)]
   if (!nextSpan && span.level != dir)
diff --git a/test/webtest-bidi.ts b/test/webtest-bidi.ts
index 0ad920d..4d3fa5b 100644
--- a/test/webtest-bidi.ts
+++ b/test/webtest-bidi.ts
@@ -1,7 +1,7 @@
 import {tempView} from "./tempview.js"
 import ist from "ist"
 import {__test, BidiSpan, Direction, Decoration, DecorationSet, EditorView} from "@codemirror/view"
-import {Text, EditorSelection, Range, StateField, Extension} from "@codemirror/state"
+import {Text, EditorSelection, SelectionRange, Range, StateField, Extension} from "@codemirror/state"
 
 function queryBrowserOrder(strings: readonly string[]) {
   let scratch = document.body.appendChild(document.createElement("div"))
@@ -104,6 +104,21 @@ function tests(dir: Direction) {
         ist(__test.moveVisually(line, order, Direction.LTR, EditorSelection.cursor(points[i], 0, 0), false)!.from, points[i - 1])
       }
     })
+
+    it("handles a misplaced non-joiner without going in a loop", () => {
+      let doc = "ءAB\u200cء", line = Text.of([doc]).line(1)
+      let order = __test.computeOrder(doc, Direction.RTL, [])
+      for (let pos: SelectionRange | null = EditorSelection.cursor(0), count = 0; count++;) {
+        ist(count, 6, "<")
+        pos = __test.moveVisually(line, order, Direction.RTL, pos, true)
+        if (!pos) break
+      }
+      for (let pos: SelectionRange | null = EditorSelection.cursor(doc.length), count = 0; count++;) {
+        ist(count, 6, "<")
+        pos = __test.moveVisually(line, order, Direction.RTL, pos, false)
+        if (!pos) break
+      }
+    })
   })
 }