Disable Fira Code ligatures in the Monaco editors

Fira Code's programming ligatures rewrote valid GraphQL into misleading
glyphs — `Int!=1` (a non-null `Int` defaulting to `1`) rendered as
`Int≠1`. Pass an explicit `font-feature-settings` string that turns
ligatures off but stays unequal to Monaco's OFF constant, so the
per-character caret measurement from the #4040 Windows fix is preserved.

Author: trevor-scheer

.changeset/disable-editor-ligatures.md

@@ -0,0 +1,5 @@
+---
+'@graphiql/react': patch
+---
+
+Disable Fira Code's font ligatures in the Monaco editors. Programming ligatures rewrote valid GraphQL into misleading glyphs — most notably `Int!=1` (a non-null `Int` with a default value of `1`) rendered as `Int≠1`, implying an inequality that isn't there. Characters now render literally. The Windows caret fix from #4040 is preserved.

packages/graphiql-react/src/utility/create-editor.ts

@@ -59,9 +59,14 @@ export function createEditor(
     },
     scrollBeyondLastLine: false, // cleans up unnecessary "padding-bottom" on each editor
     fontFamily: '"Fira Code"',
-    // Enable font ligatures and fix incorrect caret position on Windows
-    // See: https://github.com/graphql/graphiql/issues/4040
-    fontLigatures: true,
+    // Disable Fira Code's ligatures without regressing the Windows caret fix.
+    // This is deliberately an explicit `font-feature-settings` string, not
+    // `false`: Monaco only takes its monospace caret-measurement fast path when
+    // this exactly equals its OFF constant (`"liga" off, "calt" off`), and that
+    // fast path mis-positions the caret with Fira Code on Windows (#4040). Any
+    // other string keeps ligatures off while forcing per-character width
+    // measurement, so the caret stays correct. See PR #4390 for the full write-up.
+    fontLigatures: '"liga" off, "calt" off, "clig" off',
     lineNumbersMinChars: 2, // reduce line numbers width on the left size
     roundedSelection: false, // prevent multiline text selection from highlighting +1 characters after beginning/end of selection
     tabIndex: -1, // Do not allow tabbing into the editor, only via by pressing Enter or its container