Allow assuming/ensuring a default argument/operation explicitly

Author: Martchus

application/argumentparser.cpp

@@ -984,9 +984,7 @@ void ArgumentParser::readArgs(int argc, const char *const *argv)
     // check for further arguments
     if (!--argc) {
         // no arguments specified -> flag default argument as present if one is assigned
-        if (m_defaultArg) {
-            m_defaultArg->m_occurrences.emplace_back(0);
-        }
+        assumeDefaultArgument();
         return;
     }
 
@@ -1041,6 +1039,43 @@ void ArgumentParser::resetArgs()
     m_actualArgc = 0;
 }
 
+/*!
+ * \brief Assumes the default argument is present (if not already present).
+ * \remarks
+ * - Adds an occurrence to the default argument so this argument is assumed to be present (even though
+ *   it is not actually present).
+ * - This function is automatically called if there are no arguments present at all.
+ * - This function may be called manually if no actually relevant arguments are present, e.g. if only
+ *   global flags are present but no main operation argument. Note that for this concrete example there
+ *   is also ensureDefaultOperation() (which will call assumeDefaultArgument() internally).
+ */
+void ArgumentParser::assumeDefaultArgument()
+{
+    if (m_defaultArg && m_defaultArg->m_occurrences.empty()) {
+        m_defaultArg->m_occurrences.emplace_back(0);
+    }
+}
+
+/*!
+ * \brief Ensures a main operation argument is present.
+ * \remarks
+ * - Assumes the default argument is present if no other main operation argument or the help argument
+ *   is present.
+ * - Requires the default argument to be an operation argument.
+ */
+void ArgumentParser::ensureDefaultOperation()
+{
+    if (!m_defaultArg || m_defaultArg->isPresent() || !m_defaultArg->denotesOperation()) {
+        return;
+    }
+    for (auto *const arg : m_mainArgs) {
+        if (arg->isPresent() && (arg->denotesOperation() || arg == &m_helpArg)) {
+            return;
+        }
+    }
+    assumeDefaultArgument();
+}
+
 /*!
  * \brief Returns the first operation argument specified by the user or nullptr if no operation has been specified.
  * \remarks Only main arguments are considered. See Argument::specifiedOperation() to check sub arguments of a specific

application/argumentparser.h

@@ -473,6 +473,8 @@ class CPP_UTILITIES_EXPORT ArgumentParser {
         = ParseArgumentBehavior::CheckConstraints | ParseArgumentBehavior::InvokeCallbacks | ParseArgumentBehavior::ExitOnFailure);
     void readArgs(int argc, const char *const *argv);
     void resetArgs();
+    void assumeDefaultArgument();
+    void ensureDefaultOperation();
     void checkConstraints();
     void invokeCallbacks();