Translate the filter string error at display time

Keep the parser message untranslated so FilterStringLog stays in the source
language, and format the user-facing text in error() instead. That gives both
consumers what they need without localizing the log.

Q_DECLARE_TR_FUNCTIONS provides the tr() context without deriving from QObject,
which would have deleted copy/move assignment and broken the by-value uses in
PlayerActions and ViewZone. Drop the unreachable line-number branch; peglib
reports 1-based lines, so every message keeps master's "position" wording.

Co-authored-by: Lukas Brübach <44814898+BruebachL@users.noreply.github.com>

libcockatrice_filters/libcockatrice/filters/filter_string.cpp

@@ -506,6 +506,14 @@ FilterString::FilterString()
     _error = "Not initialized";
 }
 
+QString FilterString::error() const
+{
+    if (_errorColumn == 0) {
+        return _error;
+    }
+    return tr("Error at position %1: %2").arg(_errorColumn).arg(_error);
+}
+
 FilterString::FilterString(const QString &expr, const CardSearchLanguage &searchLanguage)
 {
     QByteArray ba = expr.simplified().toUtf8();
@@ -522,7 +530,8 @@ FilterString::FilterString(const QString &expr, const CardSearchLanguage &search
     searchLanguageContext = searchLanguage;
 
     search.set_logger([&](size_t /*ln*/, size_t col, const std::string &msg) {
-        _error = QString("Error at position %1: %2").arg(col).arg(QString::fromStdString(msg));
+        _error = QString::fromStdString(msg);
+        _errorColumn = col;
     });
 
     if (!search.parse(ba.data(), result)) {

libcockatrice_filters/libcockatrice/filters/filter_string.h

@@ -7,6 +7,7 @@
 #ifndef FILTER_STRING_H
 #define FILTER_STRING_H
 
+#include <QCoreApplication>
 #include <QLoggingCategory>
 #include <QString>
 #include <functional>
@@ -33,6 +34,8 @@ typedef AstBase<EmptyType> Ast;
 
 class FilterString
 {
+    Q_DECLARE_TR_FUNCTIONS(FilterString)
+
 public:
     FilterString();
     explicit FilterString(const QString &exp, const CardSearchLanguage &searchLanguage = {});
@@ -45,18 +48,18 @@ public:
         return result(card);
     }
 
-    bool valid()
+    [[nodiscard]] bool valid() const
     {
         return _error.isEmpty();
     }
 
-    QString error()
+    [[nodiscard]] QString error() const;
-    {
-        return _error;
-    }
 
 private:
+    // Untranslated parser message; error() adds the translated prefix, logging uses it as-is.
     QString _error;
+    // Column reported by the parser, or 0 when the message carries no position.
+    size_t _errorColumn = 0;
     Filter result;
 };
 

tests/carddatabase/filter_string_test.cpp

@@ -279,6 +279,22 @@ TEST_F(SetQuery, ComparisonMatchesByReleaseDate)
     EXPECT_FALSE(FilterString("set<EOE").check(inBothSets));
 }
 
+TEST(FilterStringError, InvalidExpressionIsInvalidAndReportsAPosition)
+{
+    const FilterString filter("t:(");
+
+    EXPECT_FALSE(filter.valid());
+    EXPECT_TRUE(filter.error().contains("position")) << "unexpected error text: " << filter.error().toStdString();
+}
+
+TEST(FilterStringError, ValidExpressionHasNoError)
+{
+    const FilterString filter("t:creature");
+
+    EXPECT_TRUE(filter.valid());
+    EXPECT_TRUE(filter.error().isEmpty());
+}
+
 int main(int argc, char **argv)
 {
     ::testing::InitGoogleTest(&argc, argv);