SongFilter: add class NotSongFilter

doc/protocol.xml

@@ -278,6 +278,12 @@
 
         <listitem>
           <para>
+            "<code>(!EXPRESSION)</code>": negate an expression.
+          </para>
+        </listitem>
+
+        <listitem>
+          <para>
             "<code>(EXPRESSION1 AND EXPRESSION2 ...)</code>": combine two or
             more expressions with logical "and".
           </para>

src/song/Filter.cxx

@@ -19,6 +19,7 @@
 
 #include "config.h"
 #include "Filter.hxx"
+#include "NotSongFilter.hxx"
 #include "UriSongFilter.hxx"
 #include "BaseSongFilter.hxx"
 #include "TagSongFilter.hxx"
@@ -214,6 +215,20 @@ SongFilter::ParseExpression(const char *&s, bool fold_case)
 		}
 	}
 
+	if (*s == '!') {
+		s = StripLeft(s + 1);
+
+		if (*s != '(')
+			throw std::runtime_error("'(' expected");
+
+		auto inner = ParseExpression(s, fold_case);
+		if (*s != ')')
+			throw std::runtime_error("')' expected");
+		s = StripLeft(s + 1);
+
+		return std::make_unique<NotSongFilter>(std::move(inner));
+	}
+
 	auto type = ExpectFilterType(s);
 
 	if (type == LOCATE_TAG_MODIFIED_SINCE) {

src/song/NotSongFilter.hxx

+/*
+ * Copyright 2003-2018 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_NOT_SONG_FILTER_HXX
+#define MPD_NOT_SONG_FILTER_HXX
+
+#include "ISongFilter.hxx"
+
+/**
+ * Negate an #ISongFilter.
+ */
+class NotSongFilter final : public ISongFilter {
+	ISongFilterPtr child;
+
+public:
+	template<typename C>
+	explicit NotSongFilter(C &&_child) noexcept
+		:child(std::forward<C>(_child)) {}
+
+	/* virtual methods from ISongFilter */
+	ISongFilterPtr Clone() const noexcept override {
+		return std::make_unique<NotSongFilter>(child->Clone());
+	}
+
+	std::string ToExpression() const noexcept override {
+		return "(!" + child->ToExpression() + ")";
+	}
+
+	bool Match(const LightSong &song) const noexcept override {
+		return !child->Match(song);
+	}
+};
+
+#endif