[Icons] Add SVG currentColor sentinel resolver

Qt's SVG renderer has no CSS cascade, so an authored `currentColor` never
resolves. Resolve the sentinel to a concrete palette color as plain bytes,
before the SVG reaches QSvgRenderer.

libcockatrice_utility/CMakeLists.txt

@@ -12,6 +12,7 @@ set(UTILITY_SOURCES
     libcockatrice/utility/passwordhasher.cpp
     libcockatrice/utility/report_categories.cpp
     libcockatrice/utility/server_rate_limiter.cpp
+    libcockatrice/utility/svg_recolor.cpp
     libcockatrice/utility/translation_loader.cpp
     libcockatrice/utility/user_data_backup.cpp
     libcockatrice/utility/warning_categories.cpp
@@ -35,6 +36,7 @@ set(UTILITY_HEADERS
     libcockatrice/utility/zone_names.h
     libcockatrice/utility/days_years_between.h
     libcockatrice/utility/server_rate_limiter.h
+    libcockatrice/utility/svg_recolor.h
     libcockatrice/utility/translation_loader.h
     libcockatrice/utility/user_data_backup.h
     libcockatrice/utility/warning_categories.h

libcockatrice_utility/libcockatrice/utility/svg_recolor.cpp

@@ -0,0 +1,15 @@
+#include "svg_recolor.h"
+
+#include <QString>
+
+QByteArray resolveSvgColorSentinel(const QByteArray &svg, const QByteArray &color)
+{
+    const QString source = QString::fromUtf8(svg);
+    if (!source.contains(QStringLiteral("currentColor"), Qt::CaseInsensitive)) {
+        return svg;
+    }
+
+    QString resolved = source;
+    resolved.replace(QStringLiteral("currentColor"), QString::fromLatin1(color), Qt::CaseInsensitive);
+    return resolved.toUtf8();
+}

libcockatrice_utility/libcockatrice/utility/svg_recolor.h

@@ -0,0 +1,26 @@
+/**
+ * @file svg_recolor.h
+ * @ingroup Core
+ */
+
+#ifndef SVG_RECOLOR_H
+#define SVG_RECOLOR_H
+
+#include <QByteArray>
+
+/**
+ * @brief Resolves the `currentColor` sentinel in authored SVG data.
+ *
+ * Qt's SVG renderer has no CSS cascade or ambient color context, so the
+ * sentinel is not resolved by Qt. Callers pass the concrete color they want
+ * (for example a QPalette role serialized to #RRGGBB) and receive SVG bytes
+ * that are safe to hand to QSvgRenderer.
+ *
+ * @param svg UTF-8 SVG source. Every `currentColor` occurrence, in any case,
+ *            is replaced.
+ * @param color Concrete SVG color (for example "#ff00ff"), as ASCII bytes.
+ * @return The recolored SVG source; the input is left untouched.
+ */
+QByteArray resolveSvgColorSentinel(const QByteArray &svg, const QByteArray &color);
+
+#endif // SVG_RECOLOR_H

tests/CMakeLists.txt

@@ -177,6 +177,7 @@ cockatrice_add_test(NAME test_age_formatting SOURCES test_age_formatting.cpp LIB
 cockatrice_add_test(NAME user_data_backup_test SOURCES user_data_backup_test.cpp LIBS libcockatrice_utility)
 cockatrice_add_test(NAME password_hash_test SOURCES password_hash_test.cpp LIBS libcockatrice_utility)
 cockatrice_add_test(NAME report_categories_test SOURCES report_categories_test.cpp LIBS libcockatrice_utility)
+cockatrice_add_test(NAME svg_recolor_test SOURCES svg_recolor_test.cpp LIBS libcockatrice_utility)
 cockatrice_add_test(NAME warning_categories_test SOURCES warning_categories_test.cpp LIBS libcockatrice_utility)
 cockatrice_add_test(
   NAME

tests/svg_recolor_test.cpp

@@ -0,0 +1,53 @@
+#include "libcockatrice/utility/svg_recolor.h"
+
+#include <QByteArray>
+#include <gtest/gtest.h>
+
+namespace
+{
+
+TEST(SvgRecolor, ReplacesEverySentinel)
+{
+    const QByteArray svg = R"(<svg><path fill="currentColor"/><path stroke="currentColor"/></svg>)";
+    const QByteArray result = resolveSvgColorSentinel(svg, "#ff8800");
+
+    EXPECT_EQ(result.count("#ff8800"), 2);
+    EXPECT_FALSE(result.contains("currentColor"));
+}
+
+TEST(SvgRecolor, ReplacesSentinelRegardlessOfCase)
+{
+    const QByteArray svg = R"(<svg><path fill="CurrentColor"/><path stroke="CURRENTCOLOR"/></svg>)";
+
+    EXPECT_EQ(resolveSvgColorSentinel(svg, "#ff8800").count("#ff8800"), 2);
+}
+
+TEST(SvgRecolor, LeavesTheRestOfTheDocumentIntact)
+{
+    const QByteArray svg =
+        R"(<svg viewBox="0 0 24 24"><!-- an ordinary comment --><path d="M0 0h24v24" fill="currentColor"/></svg>)";
+    const QByteArray result = resolveSvgColorSentinel(svg, "#123456");
+
+    EXPECT_TRUE(result.contains(R"(viewBox="0 0 24 24")"));
+    EXPECT_TRUE(result.contains(R"(d="M0 0h24v24")"));
+    EXPECT_TRUE(result.contains("an ordinary comment"));
+}
+
+TEST(SvgRecolor, DoesNotModifyTheInput)
+{
+    const QByteArray svg = R"(<svg><path fill="currentColor"/></svg>)";
+    const QByteArray original = svg;
+
+    resolveSvgColorSentinel(svg, "#000000");
+
+    EXPECT_EQ(svg, original);
+}
+
+TEST(SvgRecolor, NoSentinelIsANoOp)
+{
+    const QByteArray svg = R"(<svg><path fill="#abcdef"/></svg>)";
+
+    EXPECT_EQ(resolveSvgColorSentinel(svg, "#ffffff"), svg);
+}
+
+} // namespace