Fix cursor positioning for files containing emoji (#13340)

Co-authored-by: Georgii Dolzhykov <thorn.mailbox@gmail.com>

changelog_unreleased/javascript/13340.md

@@ -0,0 +1,16 @@
+#### Fix cursor positioning for files containing emoji (#13340 by @fisker)
+
+```console
+$ cat test.js
+const { formatWithCursor } = await import("prettier");
+const code = "'😀😀😀😀'";
+await formatWithCursor(code, {parser: "babel", cursorOffset: 9})
+
+# Prettier stable
+$ node test.js
+{ formatted: '"😀😀😀😀";\n', cursorOffset: 5, comments: [] }
+
+# Prettier main
+$ node test.js
+{ formatted: '"😀😀😀😀";\n', cursorOffset: 9, comments: [] }
+```

src/main/core.js

@@ -105,14 +105,16 @@ async function coreFormat(originalText, opts, addAlignmentSize = 0) {
     // diff old and new cursor node texts, with a special cursor
     // symbol inserted to find out where it moves to
 
-    const oldCursorNodeCharArray = [...oldCursorNodeText];
+    // eslint-disable-next-line unicorn/prefer-spread
+    const oldCursorNodeCharArray = oldCursorNodeText.split("");
     oldCursorNodeCharArray.splice(
       cursorOffsetRelativeToOldCursorNode,
       0,
       CURSOR
     );
 
-    const newCursorNodeCharArray = [...newCursorNodeText];
+    // eslint-disable-next-line unicorn/prefer-spread
+    const newCursorNodeCharArray = newCursorNodeText.split("");
 
     const cursorNodeDiff = diffArrays(
       oldCursorNodeCharArray,

tests/format/js/cursor/__snapshots__/jsfmt.spec.js.snap

@@ -271,6 +271,21 @@ const y = 5;
 ================================================================================
 `;
 
+exports[`cursor-emoji.js format 1`] = `
+====================================options=====================================
+cursorOffset: 9
+parsers: ["babel", "typescript", "flow"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+"😀😀😀😀<|>"
+
+=====================================output=====================================
+"😀😀😀😀<|>";
+
+================================================================================
+`;
+
 exports[`file-start-with-comment-1.js format 1`] = `
 ====================================options=====================================
 cursorOffset: 5

tests/format/js/cursor/cursor-emoji.js

@@ -0,0 +1 @@
+"😀😀😀😀<|>"