From 6b7a77b4b201595e309bc3f5c60358ea6aedaefc Mon Sep 17 00:00:00 2001
From: Maria Florencia Besteiro Gonzalez
 <florencia.besteiro-gonzalez@overleaf.com>
Date: Fri, 7 Aug 2026 14:29:18 +0200
Subject: [PATCH] Merge pull request #36239 from
 overleaf/mfb-show-duplicate-in-visual-bib-editor

Show duplicate entries in visual bib editor

GitOrigin-RevId: 32e4e41a751624a2142c7fd2c5e5de5a5d3905f5
---
 .../js/features/bibtex/bibtex-entry.mts       | 20 ++++++++++++++++---
 services/web/locales/en.json                  |  2 +-
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/services/web/frontend/js/features/bibtex/bibtex-entry.mts b/services/web/frontend/js/features/bibtex/bibtex-entry.mts
index 00b3bc18bc..2f6e456c7c 100644
--- a/services/web/frontend/js/features/bibtex/bibtex-entry.mts
+++ b/services/web/frontend/js/features/bibtex/bibtex-entry.mts
@@ -9,6 +9,7 @@ type BibtexEntryOptions = {
   key?: string
   fields?: Fields
   id?: string
+  occurrenceIndex?: number
   updatedAt?: Date
 }
 
@@ -41,11 +42,22 @@ export class BibtexEntry {
   private readonly _id: string
 
   /**
-   * Stable identifier. Defaults to the citation key for in-project entries;
-   * set to the database record ID for library entries.
+   * Position of this entry among entries that share its citation key, in
+   * document order (0-based). In-project entries can share a citation key, so
+   * this disambiguates them. It is positional metadata (not content), assigned
+   * by `useBibtexEntries` once the full, ordered entry list is known.
+   */
+  occurrenceIndex: number
+
+  /**
+   * Stable identifier.
+   * - Library entries: the database record ID.
+   * - In-project entries: `${key}#${occurrenceIndex}`, so duplicate keys still
+   *   get distinct ids and can be located unambiguously in the document.
    */
   get id(): string {
-    return this._id || this.key
+    if (this._id) return this._id
+    return `${this.key}#${this.occurrenceIndex}`
   }
 
   constructor({
@@ -53,12 +65,14 @@ export class BibtexEntry {
     key = '',
     fields = new Map(),
     id = '',
+    occurrenceIndex = 0,
     updatedAt,
   }: BibtexEntryOptions = {}) {
     this.type = type
     this.key = key
     this.fields = fields
     this._id = id
+    this.occurrenceIndex = occurrenceIndex
     this.updatedAt = updatedAt
   }
 
diff --git a/services/web/locales/en.json b/services/web/locales/en.json
index 0f51c0d9dc..22ff548fc5 100644
--- a/services/web/locales/en.json
+++ b/services/web/locales/en.json
@@ -289,7 +289,7 @@
   "biblatex": "BibLaTeX",
   "bibliographies": "Bibliographies",
   "bibtex": "BibTeX",
-  "bibtex_duplicates_keys": "The file __fileName__ contains more than one entry with the citation key __key__. Only the first occurrence is shown in this list.",
+  "bibtex_duplicates_keys": "This citation key is used by another entry. Duplicate keys cause citation errors — rename this key or delete one of the entries.",
   "billed_annually_at": "Billed annually at <0>__price__</0> <1>(includes plan and any add-ons)</1>",
   "billed_monthly_at": "Billed monthly at <0>__price__</0> <1>(includes plan and any add-ons)</1>",
   "billed_yearly": "billed yearly",