Add support for jumping without resetting the callstack

inkcpp/include/runner.h

@@ -62,9 +62,13 @@ class runner_interface
 	 * to the content at the specified path.
 	 *
 	 * @param path path to search and move execution to
+	 * @param reset_callstack If true, discard the call stack when moving.
+	 * This is the default, safe, behaviour. Otherwise retain the current
+	 * stack as far as possible.
+	 * 
 	 * @return If the path was found
 	 */
-	virtual bool move_to(hash_t path) = 0;
+	virtual bool move_to(hash_t path, bool reset_callstack = true) = 0;
 
 	/**
 	 * Moves the runner to the specified path.
@@ -73,9 +77,12 @@ class runner_interface
 	 * to the content at the specified path.
 	 *
 	 * @param path path to search and move execution to
+	 * @param reset_callstack If true, discard the call stack when moving.
+	 * This is the default, safe, behaviour. Otherwise retain the current
+	 * stack as far as possible.
 	 * @return If the path was found
 	 */
-	bool move_to(const char* path) { return move_to(ink::hash_string(path)); }
+	bool move_to(const char* path, bool reset_callstack = true) { return move_to(ink::hash_string(path), reset_callstack); }
 
 	/**
 	 * Can the runner continue?

inkcpp/runner_impl.cpp

@@ -823,7 +823,7 @@ const char* runner_impl::getline_alloc()
 	return res;
 }
 
-bool runner_impl::move_to(hash_t path)
+bool runner_impl::move_to(hash_t path, bool reset_callstack)
 {
 	// find the path
 	ip_t destination = _story->find_offset_for(path);
@@ -832,9 +832,13 @@ bool runner_impl::move_to(hash_t path)
 		return false;
 	}
 
-	// Clear state and move to destination
-	reset();
-	_ptr = _story->instructions();
+	// Clear state if requested,
+	if (reset_callstack) {
+		reset();
+		_ptr = _story->instructions();
+	}
+
+	// Don't track visit (are we sure this is right?)
 	const bool record_visits    = false;
 	const bool track_knot_visit = false;
 	jump(destination, record_visits, track_knot_visit);

inkcpp/runner_impl.h

@@ -129,7 +129,7 @@ class runner_impl
 	virtual const char* getline_alloc() override;
 
 	// move to path
-	virtual bool move_to(hash_t path) override;
+	virtual bool move_to(hash_t path, bool reset_callstack = true) override;
 
 	// move to path but keep as much state as possible
 	bool migrate_to(const loader& loader, hash_t path);