Allow kreadconfig/kwriteconfig to access the root group

The default group if "--group" is not specified is "KDE".
Trying to specify a null group name causes an assert in KConfigGroup::groupImpl().
Explicitly detect and give an error message for a null group name.
Mention in the help text that "<default>" can be used to specify the root group -
this string comes from KConfigGroupPrivate::name().

Add the missing parser.addHelpOption() for kreadconfig.
Update the help strings.
Apply clang-format changes.
    
I18N:

2 files changed, 28 insertions, 8 deletions

diff --git a/src/kreadconfig/kreadconfig.cpp b/src/kreadconfig/kreadconfig.cpp
index 01d44326..7e96a17a 100644
--- a/src/kreadconfig/kreadconfig.cpp
+++ b/src/kreadconfig/kreadconfig.cpp
@@ -41,12 +41,14 @@ int main(int argc, char **argv)
     QCoreApplication app(argc, argv);
 
     QCommandLineParser parser;
+    parser.addHelpOption();
     parser.addOption(
         QCommandLineOption(QStringLiteral("file"), QCoreApplication::translate("main", "Use <file> instead of global config"), QStringLiteral("file")));
-    parser.addOption(QCommandLineOption(QStringLiteral("group"),
-                                        QCoreApplication::translate("main", "Group to look in. Use repeatedly for nested groups."),
-                                        QStringLiteral("group"),
-                                        QStringLiteral("KDE")));
+    parser.addOption(
+        QCommandLineOption(QStringLiteral("group"),
+                           QCoreApplication::translate("main", "Group to look in. Use \"<default>\" for the root group, or use repeatedly for nested groups."),
+                           QStringLiteral("group"),
+                           QStringLiteral("KDE")));
     parser.addOption(QCommandLineOption(QStringLiteral("key"), QCoreApplication::translate("main", "Key to look for"), QStringLiteral("key")));
     parser.addOption(QCommandLineOption(QStringLiteral("default"), QCoreApplication::translate("main", "Default value"), QStringLiteral("value")));
     parser.addOption(QCommandLineOption(QStringLiteral("type"), QCoreApplication::translate("main", "Type of variable"), QStringLiteral("type")));
@@ -75,6 +77,16 @@ int main(int argc, char **argv)
     }
     KConfigGroup cfgGroup = konfig->group(QString());
     for (const QString &grp : groups) {
+        if (grp.isEmpty()) {
+            fprintf(stderr,
+                    "%s: %s\n",
+                    qPrintable(QCoreApplication::applicationName()),
+                    qPrintable(QCoreApplication::translate("main", "Group name cannot be empty, use \"<default>\" for the root group")));
+            if (configMustDeleted) {
+                delete konfig;
+            }
+            return 2;
+        }
         cfgGroup = cfgGroup.group(grp);
     }
 
diff --git a/src/kreadconfig/kwriteconfig.cpp b/src/kreadconfig/kwriteconfig.cpp
index 20036331..af39325e 100644
--- a/src/kreadconfig/kwriteconfig.cpp
+++ b/src/kreadconfig/kwriteconfig.cpp
@@ -23,10 +23,11 @@ int main(int argc, char **argv)
     parser.addHelpOption();
     parser.addOption(
         QCommandLineOption(QStringLiteral("file"), QCoreApplication::translate("main", "Use <file> instead of global config"), QStringLiteral("file")));
-    parser.addOption(QCommandLineOption(QStringLiteral("group"),
-                                        QCoreApplication::translate("main", "Group to look in. Use repeatedly for nested groups."),
-                                        QStringLiteral("group"),
-                                        QStringLiteral("KDE")));
+    parser.addOption(
+        QCommandLineOption(QStringLiteral("group"),
+                           QCoreApplication::translate("main", "Group to look in. Use \"<default>\" for the root group, or use repeatedly for nested groups."),
+                           QStringLiteral("group"),
+                           QStringLiteral("KDE")));
     parser.addOption(QCommandLineOption(QStringLiteral("key"), QCoreApplication::translate("main", "Key to look for"), QStringLiteral("key")));
     parser.addOption(
         QCommandLineOption(QStringLiteral("type"),
@@ -61,6 +62,13 @@ int main(int argc, char **argv)
 
     KConfigGroup cfgGroup = konfig->group(QString());
     for (const QString &grp : groups) {
+        if (grp.isEmpty()) {
+            fprintf(stderr,
+                    "%s: %s\n",
+                    qPrintable(QCoreApplication::applicationName()),
+                    qPrintable(QCoreApplication::translate("main", "Group name cannot be empty, use \"<default>\" for the root group")));
+            return 2;
+        }
         cfgGroup = cfgGroup.group(grp);
     }