From 341b1c1c3e2e44690540fb06b9aa140ddcf17fe5 Mon Sep 17 00:00:00 2001
From: Lain Soykaf <lain@lain.com>
Date: Tue, 11 Aug 2026 21:51:24 +0400
Subject: [PATCH] fix: restore Theme 2 font families

---
 changelog.d/theme2-font-cache.fix             |  1 +
 src/services/style_setter/style_setter.js     |  8 +++-
 src/services/theme_data/theme2_to_theme3.js   |  2 +-
 .../style_setter/style_setter.spec.js         | 24 +++++++++++
 .../theme_data/theme2_to_theme3.spec.js       | 42 +++++++++++++++++++
 5 files changed, 75 insertions(+), 2 deletions(-)
 create mode 100644 changelog.d/theme2-font-cache.fix
 create mode 100644 test/unit/specs/services/style_setter/style_setter.spec.js
 create mode 100644 test/unit/specs/services/theme_data/theme2_to_theme3.spec.js

diff --git a/changelog.d/theme2-font-cache.fix b/changelog.d/theme2-font-cache.fix
new file mode 100644
index 000000000..d8782b467
--- /dev/null
+++ b/changelog.d/theme2-font-cache.fix
@@ -0,0 +1 @@
+Fix Theme 2 fonts falling back to serif after upgrade
diff --git a/src/services/style_setter/style_setter.js b/src/services/style_setter/style_setter.js
index 318978264..d42c5793f 100644
--- a/src/services/style_setter/style_setter.js
+++ b/src/services/style_setter/style_setter.js
@@ -92,6 +92,11 @@ export const adoptStyleSheets = throttle(() => {
 const EAGER_STYLE_ID = 'pleroma-eager-styles'
 const LAZY_STYLE_ID = 'pleroma-lazy-styles'
 
+export const hasInvalidCachedThemeRules = (data) =>
+  data
+    .flat()
+    .some((rule) => /--(?:mono)?font:\s*\[object Object\](?:;|$)/i.test(rule))
+
 const generateTheme = (inputRuleset, callbacks, debug) => {
   const {
     onNewRule = () => {
@@ -151,7 +156,8 @@ export const tryLoadCache = async () => {
     if (
       cache.engineChecksum === getEngineChecksum() &&
       cache.checksum !== undefined &&
-      cache.checksum === useMergedConfigStore().mergedConfig.themeChecksum
+      cache.checksum === useMergedConfigStore().mergedConfig.themeChecksum &&
+      !hasInvalidCachedThemeRules(cache.data)
     ) {
       const eagerStyles = createStyleSheet(EAGER_STYLE_ID, 10)
       const lazyStyles = createStyleSheet(LAZY_STYLE_ID, 20)
diff --git a/src/services/theme_data/theme2_to_theme3.js b/src/services/theme_data/theme2_to_theme3.js
index 8c3ac6ad2..48afe4ad9 100644
--- a/src/services/theme_data/theme2_to_theme3.js
+++ b/src/services/theme_data/theme2_to_theme3.js
@@ -266,7 +266,7 @@ export const convertTheme2To3 = (data) => {
     Object.keys(data.fonts || {}).forEach((key) => {
       if (!fontsKeys.has(key)) return
       if (!data.fonts[key]) return
-      const originalFont = data.fonts[key]
+      const originalFont = data.fonts[key].family
       const rule = { source: '2to3' }
 
       switch (key) {
diff --git a/test/unit/specs/services/style_setter/style_setter.spec.js b/test/unit/specs/services/style_setter/style_setter.spec.js
new file mode 100644
index 000000000..c1bacdfa1
--- /dev/null
+++ b/test/unit/specs/services/style_setter/style_setter.spec.js
@@ -0,0 +1,24 @@
+import { hasInvalidCachedThemeRules } from 'src/services/style_setter/style_setter.js'
+
+describe('style setter cache', () => {
+  it('rejects cached rules containing serialized objects', () => {
+    expect(
+      hasInvalidCachedThemeRules([
+        ['html { --font: [object Object]; }'],
+        ['.post { --font: sans-serif; }'],
+      ]),
+    ).to.equal(true)
+  })
+
+  it('accepts cached rules containing valid font families', () => {
+    expect(
+      hasInvalidCachedThemeRules([
+        ['html { --font: sans-serif; }'],
+        [
+          '.post { --font: "Atkinson Hyperlegible"; }',
+          '.post::after { content: "[object Object]"; }',
+        ],
+      ]),
+    ).to.equal(false)
+  })
+})
diff --git a/test/unit/specs/services/theme_data/theme2_to_theme3.spec.js b/test/unit/specs/services/theme_data/theme2_to_theme3.spec.js
new file mode 100644
index 000000000..7165d88db
--- /dev/null
+++ b/test/unit/specs/services/theme_data/theme2_to_theme3.spec.js
@@ -0,0 +1,42 @@
+import {
+  basePaletteKeys,
+  convertTheme2To3,
+} from 'src/services/theme_data/theme2_to_theme3.js'
+
+describe('Theme 2 to Theme 3 conversion', () => {
+  it('converts font descriptors to CSS font families', () => {
+    const colors = Object.fromEntries(
+      [...basePaletteKeys].map((key) => [key, '#000000']),
+    )
+    const rules = convertTheme2To3({
+      colors,
+      fonts: {
+        interface: { family: 'sans-serif' },
+        input: { family: 'Open Sans' },
+        post: { family: 'Atkinson Hyperlegible' },
+        postCode: { family: 'monospace' },
+      },
+    })
+
+    expect(rules).to.deep.include({
+      source: '2to3',
+      component: 'Root',
+      directives: { '--font': 'generic | sans-serif' },
+    })
+    expect(rules).to.deep.include({
+      source: '2to3',
+      component: 'Root',
+      directives: { '--monoFont': 'generic | monospace' },
+    })
+    expect(rules).to.deep.include({
+      source: '2to3',
+      component: 'Input',
+      directives: { '--font': 'generic | Open Sans' },
+    })
+    expect(rules).to.deep.include({
+      source: '2to3',
+      component: 'RichContent',
+      directives: { '--font': 'generic | Atkinson Hyperlegible' },
+    })
+  })
+})