From 41d95abc5c1067690d1d5eb111b587055286d233 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bel=C3=A9n=20Albeza?= <belen.albeza@kaleidos.net>
Date: Tue, 20 Oct 2026 14:09:01 +0200
Subject: [PATCH] :bug: Fix math symbols rendered as boxes in the new render
 engine (#12471)

Noto Sans Symbols lacks most arrows and math operators. Fall back to
Noto Sans Math for them, and to Noto Sans for letterlike symbols.

Closes #12469

AI-assisted-by: claude-opus-5-5
---
 common/src/app/common/fonts.cljs         | 11 +++++--
 common/test/common_tests/fonts_test.cljs | 37 ++++++++++++++++++++++++
 common/test/common_tests/runner.cljc     |  2 ++
 3 files changed, 48 insertions(+), 2 deletions(-)
 create mode 100644 common/test/common_tests/fonts_test.cljs

diff --git a/common/src/app/common/fonts.cljs b/common/src/app/common/fonts.cljs
index 237a6b362b..ee96b6c9df 100644
--- a/common/src/app/common/fonts.cljs
+++ b/common/src/app/common/fonts.cljs
@@ -213,7 +213,12 @@
    ;; SMP: Mahjong/Domino/Playing Cards (U+1F000-1F0FF), Supplemental Arrows-C (U+1F800-1F8FF),
    ;;      Legacy Computing Symbols (U+1FB00-1FBFF)
    :symbols-2   #"[\u2190-\u21FF\u2200-\u22FF\u2300-\u23FF\u25A0-\u25FF\u2600-\u26FF\u2700-\u27BF\u2B00-\u2BFF]|\uD83C[\uDC00-\uDCFF]|\uD83E[\uDC00-\uDCFF\uDF00-\uDFFF]"
-   :music       #"[\u2669-\u267B]|\uD834[\uDD00-\uDD1F]"})
+   :music       #"[\u2669-\u267B]|\uD834[\uDD00-\uDD1F]"
+   ;; Arrows, Mathematical Operators, Misc Mathematical Symbols A/B, Supplemental
+   ;; Arrows A/B, Supplemental Math Operators: the Symbols fonts lack most of them
+   :math        #"[\u2190-\u21FF\u2200-\u22FF\u27C0-\u27FF\u2900-\u2AFF]"
+   ;; Letterlike Symbols (ℝ, ℕ, ℃, ™, ...)
+   :letterlike  #"[\u2100-\u214F]"})
 
 (defn contains-emoji? [text]
   (let [result (re-find emoji-pattern text)]
@@ -292,7 +297,9 @@
    :meroitic    {:font-id "gfont-noto-sans-meroitic"      :font-variant-id "regular" :style 0 :weight 400 :is-fallback true}
    :symbols     {:font-id "gfont-noto-sans-symbols"       :font-variant-id "regular" :style 0 :weight 400 :is-fallback true}
    :symbols-2   {:font-id "gfont-noto-sans-symbols-2"     :font-variant-id "regular" :style 0 :weight 400 :is-fallback true}
-   :music       {:font-id "gfont-noto-music"              :font-variant-id "regular" :style 0 :weight 400 :is-fallback true}})
+   :music       {:font-id "gfont-noto-music"              :font-variant-id "regular" :style 0 :weight 400 :is-fallback true}
+   :math        {:font-id "gfont-noto-sans-math"          :font-variant-id "regular" :style 0 :weight 400 :is-fallback true}
+   :letterlike  {:font-id "gfont-noto-sans"               :font-variant-id "regular" :style 0 :weight 400 :is-fallback true}})
 
 (defn add-noto-fonts [fonts languages]
   (reduce (fn [acc lang]
diff --git a/common/test/common_tests/fonts_test.cljs b/common/test/common_tests/fonts_test.cljs
new file mode 100644
index 0000000000..36786ccb7c
--- /dev/null
+++ b/common/test/common_tests/fonts_test.cljs
@@ -0,0 +1,37 @@
+;; This Source Code Form is subject to the terms of the Mozilla Public
+;; License, v. 2.0. If a copy of the MPL was not distributed with this
+;; file, You can obtain one at http://mozilla.org/MPL/2.0/.
+;;
+;; Copyright (c) KALEIDOS SUBSIDIARY SL
+
+(ns common-tests.fonts-test
+  (:require
+   [app.common.fonts :as cfnt]
+   [clojure.test :as t]))
+
+(defn- fallback-font-ids
+  [text]
+  (->> (cfnt/collect-used-languages #{} text)
+       (cfnt/add-noto-fonts #{})
+       (into #{} (map :font-id))))
+
+(t/deftest math-symbols-use-noto-sans-math
+  (t/testing "arrows"
+    (t/is (contains? (fallback-font-ids "↳") "gfont-noto-sans-math"))
+    (t/is (contains? (fallback-font-ids "⇒") "gfont-noto-sans-math")))
+  (t/testing "mathematical operators"
+    (t/is (contains? (fallback-font-ids "∀x ∈ A") "gfont-noto-sans-math"))
+    (t/is (contains? (fallback-font-ids "a ≠ b") "gfont-noto-sans-math")))
+  (t/testing "supplemental arrows and operators"
+    (t/is (contains? (fallback-font-ids "⟹") "gfont-noto-sans-math"))
+    (t/is (contains? (fallback-font-ids "⤴") "gfont-noto-sans-math"))
+    (t/is (contains? (fallback-font-ids "⨁") "gfont-noto-sans-math"))))
+
+(t/deftest letterlike-symbols-use-noto-sans
+  (t/is (contains? (fallback-font-ids "x ∈ ℝ") "gfont-noto-sans"))
+  (t/is (contains? (fallback-font-ids "20 ℃") "gfont-noto-sans"))
+  (t/is (contains? (fallback-font-ids "Penpot™") "gfont-noto-sans")))
+
+(t/deftest plain-text-does-not-use-noto-sans-math
+  (t/is (not (contains? (fallback-font-ids "Hello world") "gfont-noto-sans-math")))
+  (t/is (not (contains? (fallback-font-ids "★ ☀") "gfont-noto-sans-math"))))
diff --git a/common/test/common_tests/runner.cljc b/common/test/common_tests/runner.cljc
index 7a4c4243f4..e78fbf3da9 100644
--- a/common/test/common_tests/runner.cljc
+++ b/common/test/common_tests/runner.cljc
@@ -10,6 +10,7 @@
    #?(:cljs [app.common.logging :as l])
    #?(:cljs [clojure.string :as str])
    #?(:cljs [clojure.tools.cli :refer [parse-opts]])
+   #?(:cljs [common-tests.fonts-test])
    #?(:cljs [goog.object :as gobj])
    [clojure.test :as t]
    [common-tests.attrs-test]
@@ -123,6 +124,7 @@
    'common-tests.data-test
    'common-tests.exceptions-test
    'common-tests.files-builder-test
+   #?(:cljs 'common-tests.fonts-test)
    'common-tests.files-changes-test
    'common-tests.files-migrations-0025-test
    'common-tests.files-migrations-0026-test