From 2ef3670c124868bfe2cad39e78b77efb0a16c490 Mon Sep 17 00:00:00 2001
From: Mateusz <mateusz.karpow@guardian.co.uk>
Date: Fri, 27 Mar 2026 02:30:33 +0000
Subject: [PATCH] fix: detect polarity changes in programmatic value updates

---
 lib/cql/src/cqlInput/CqlInput.spec.ts      | 11 ++++++
 lib/cql/src/cqlInput/editor/diff.ts        | 39 ++++++++++++++++++++--
 lib/cql/src/cqlInput/editor/editor.spec.ts | 11 ++++++
 3 files changed, 59 insertions(+), 2 deletions(-)

diff --git a/lib/cql/src/cqlInput/CqlInput.spec.ts b/lib/cql/src/cqlInput/CqlInput.spec.ts
index bd7781f6..cc529687 100644
--- a/lib/cql/src/cqlInput/CqlInput.spec.ts
+++ b/lib/cql/src/cqlInput/CqlInput.spec.ts
@@ -78,4 +78,15 @@ describe("CqlInput", () => {
       "This event should be propagated to the input's container, as it is not handled by the editor",
     ).toBe(true);
   });
+
+  it("should update the rendered value when only the polarity changes", () => {
+    const { cqlInput } = createCqlInputContainer("+tag:one");
+    let callbackValue = "";
+    cqlInput.addEventListener(
+      "queryChange",
+      (e) => (callbackValue = e.detail.queryStr),
+    );
+    cqlInput.setAttribute("value", "-tag:one");
+    expect(callbackValue).toBe("-tag:one");
+  });
 });
diff --git a/lib/cql/src/cqlInput/editor/diff.ts b/lib/cql/src/cqlInput/editor/diff.ts
index 9913d562..a2a0b29b 100644
--- a/lib/cql/src/cqlInput/editor/diff.ts
+++ b/lib/cql/src/cqlInput/editor/diff.ts
@@ -1,10 +1,41 @@
-import { Fragment } from "prosemirror-model";
+import { Fragment, Mark, Node } from "prosemirror-model";
+import { IS_READ_ONLY, IS_SELECTED } from "./schema";
 
 /**
- * These diff functions are vendored to ignore attributes and markup, as we only care about markup.
+ * These diff functions are vendored from ProseMirror's Fragment.findDiffStart /
+ * findDiffEnd to customise attribute comparison.
+ *
+ * The originals use Node.sameMarkup, which compares ALL attributes. That
+ * causes false positives for transient editor-state attributes (IS_SELECTED,
+ * IS_READ_ONLY) that differ between the live document and an incoming document
+ * built by queryToProseMirrorDoc — see #52.
+ *
+ * We replace sameMarkup with sameContentMarkup, which skips transient attrs
+ * so the diff is blind to decorative state but still detects semantically
+ * meaningful changes like POLARITY.
+ *
  * Source: https://github.com/ProseMirror/prosemirror-model/blob/c8c7b62645d2a8293fa6b7f52aa2b04a97821f34/src/diff.ts
  */
 
+/** Attrs that are transient editor state, not query content. */
+const TRANSIENT_ATTRS: ReadonlySet<string> = new Set([IS_SELECTED, IS_READ_ONLY]);
+
+/**
+ * Like Node.sameMarkup, but ignores transient editor-state attributes.
+ */
+function sameContentMarkup(a: Node, b: Node): boolean {
+  if (a.type !== b.type || !Mark.sameSet(a.marks, b.marks)) return false;
+  for (const key in a.attrs) {
+    if (TRANSIENT_ATTRS.has(key)) continue;
+    if (a.attrs[key] !== b.attrs[key]) return false;
+  }
+  for (const key in b.attrs) {
+    if (TRANSIENT_ATTRS.has(key)) continue;
+    if (!(key in a.attrs)) return false;
+  }
+  return true;
+}
+
 export function findDiffStartForContent(
   a: Fragment,
   b: Fragment,
@@ -21,6 +52,8 @@ export function findDiffStartForContent(
       continue;
     }
 
+    if (!sameContentMarkup(childA, childB)) return pos;
+
     if (childA.isText && childA.text != childB.text) {
       for (let j = 0; childA.text![j] == childB.text![j]; j++) pos++;
       return pos;
@@ -51,6 +84,8 @@ export function findDiffEndForContent(
       continue;
     }
 
+    if (!sameContentMarkup(childA, childB)) return { a: posA, b: posB };
+
     if (childA.isText && childA.text != childB.text) {
       let same = 0;
       const minSize = Math.min(childA.text!.length, childB.text!.length);
diff --git a/lib/cql/src/cqlInput/editor/editor.spec.ts b/lib/cql/src/cqlInput/editor/editor.spec.ts
index 67a816f5..d6cc6c1b 100644
--- a/lib/cql/src/cqlInput/editor/editor.spec.ts
+++ b/lib/cql/src/cqlInput/editor/editor.spec.ts
@@ -140,4 +140,15 @@ describe("updateEditorViewWithQueryStr", () => {
 
     expect(docToCqlStrWithSelection(editorView.state)).toEqual("+tag:^$ ");
   });
+
+  it("should update the document when only the polarity of a chip changes", () => {
+    const { editorView, updateEditorView } =
+      createEditorFromInitialState("+tag:a");
+
+    expect(docToCqlStr(editorView.state.doc)).toEqual("+tag:a ");
+
+    updateEditorView("-tag:a");
+
+    expect(docToCqlStr(editorView.state.doc)).toEqual("-tag:a ");
+  });
 });