FIX: Recompile theme translations when fallback data changes (#24371)

Previously we would only recompile a theme locale when its own data changes. However, the output also includes fallback data from other locales, so we need to invalidate all locales when fallback locale data is changed. Building a list of dependent locales is tricky, so let's just invalidate them all.

app/models/theme.rb

@@ -6,7 +6,7 @@ require "json_schemer"
 class Theme < ActiveRecord::Base
   include GlobalPath
 
-  BASE_COMPILER_VERSION = 77
+  BASE_COMPILER_VERSION = 78
 
   class SettingsMigrationError < StandardError
   end

app/models/theme_field.rb

@@ -664,6 +664,8 @@ class ThemeField < ActiveRecord::Base
           name: ThemeField.scss_fields + ThemeField.html_fields,
         )
       )
+    elsif translation_field?
+      return theme.theme_fields.where(target_id: Theme.targets[:translations])
     end
     ThemeField.none
   end

spec/models/theme_field_spec.rb

@@ -595,6 +595,57 @@ HTML
         expect(fr1.javascript_cache.content).to include("helloworld")
         expect(fr1.javascript_cache.content).to include("enval1")
       end
+
+      it "is recreated when data changes" do
+        t = Fabricate(:theme)
+        t.set_field(
+          target: "translations",
+          name: "fr",
+          value: { fr: { mykey: "initial value" } }.deep_stringify_keys.to_yaml,
+        )
+        t.save!
+
+        field = t.theme_fields.find_by(target_id: Theme.targets[:translations], name: "fr")
+        expect(field.javascript_cache.content).to include("initial value")
+
+        t.set_field(
+          target: "translations",
+          name: "fr",
+          value: { fr: { mykey: "new value" } }.deep_stringify_keys.to_yaml,
+        )
+        t.save!
+
+        field = t.theme_fields.find_by(target_id: Theme.targets[:translations], name: "fr")
+        expect(field.javascript_cache.reload.content).to include("new value")
+      end
+
+      it "is recreated when fallback data changes" do
+        t = Fabricate(:theme)
+        t.set_field(
+          target: "translations",
+          name: "fr",
+          value: { fr: {} }.deep_stringify_keys.to_yaml,
+        )
+        t.set_field(
+          target: "translations",
+          name: "en",
+          value: { en: { myotherkey: "initial value" } }.deep_stringify_keys.to_yaml,
+        )
+        t.save!
+
+        field = t.theme_fields.find_by(target_id: Theme.targets[:translations], name: "fr")
+        expect(field.javascript_cache.content).to include("initial value")
+
+        t.set_field(
+          target: "translations",
+          name: "en",
+          value: { en: { myotherkey: "new value" } }.deep_stringify_keys.to_yaml,
+        )
+        t.save!
+
+        field = t.theme_fields.find_by(target_id: Theme.targets[:translations], name: "fr")
+        expect(field.javascript_cache.reload.content).to include("new value")
+      end
     end
 
     describe "prefix injection" do