QQStyleKitTheme: Keep the font resolve mask when merging font scopes

QFont::resolve() returns only the left-hand operand's resolve mask,
unlike QPalette::resolve() which ORs both, so each step of the fallback
chain in updateThemeFonts() collapsed the accumulated mask down to the
nearest layer's. Setting fonts.system.bold in a theme therefore produced
a font still holding the style's family and pointSize as values, but
with a mask claiming only Weight. To fix, set the resolve mask to the
union explicitly.

Pick-to: 6.12
Change-Id: Ib802a8ce3d8a5760bc9639631080a25d5e2658df
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

1 files changed, 11 insertions, 2 deletions

diff --git a/src/labs/stylekit/qqstylekittheme.cpp b/src/labs/stylekit/qqstylekittheme.cpp
index a0dfdb7d4f..6edb8de25c 100644
--- a/src/labs/stylekit/qqstylekittheme.cpp
+++ b/src/labs/stylekit/qqstylekittheme.cpp
@@ -197,6 +197,15 @@ void QQStyleKitTheme::updateThemeFonts()
     for (auto *fb = fonts; fb; fb = fb->fallbackFont())
         fbChain.append(fb);
 
+    // QFont::resolve() keeps only the left-hand operand's resolve mask.
+    // Restore the mask explicitly, or every attribute contributed by an
+    // earlier layer of the chain is dropped again by font resolution.
+    auto merge = [](const QFont &a, const QFont &b) {
+        QFont merged = a.resolve(b);
+        merged.setResolveMask(b.resolveMask() | a.resolveMask());
+        return merged;
+    };
+
     auto resolveFromFontChain = [&](QQuickTheme::Scope scope) -> QFont
     {
         QFont result;
@@ -206,10 +215,10 @@ void QQStyleKitTheme::updateThemeFonts()
             const QQStyleKitFont *fb = fbChain[i];
             // Apply system font first as a base, and override with scope-specific font
             if (scope != QQuickTheme::System && fb->isSet(QQuickTheme::System)) {
-                result = fb->fontForScope(QQuickTheme::System).resolve(result);
+                result = merge(fb->fontForScope(QQuickTheme::System), result);
             }
             if (fb->isSet(scope)) {
-                result = fb->fontForScope(scope).resolve(result);
+                result = merge(fb->fontForScope(scope), result);
             }
         }