db: fix broken command "list ... group"

Grouping in the "list" command was completely broken from the start,
unlike "count group".  I have no idea what I have been thinking when I
wrote commit ae178c77bdc47c954fd9a4b32ffc07fe6c4a8a49, but it didn't
make any sense.

This commit is a rewrite of the feature.

For clients to be able to detect this feature, this commit also
increments the protocol version.

2 files changed, 0 insertions, 190 deletions

diff --git a/src/tag/Set.cxx b/src/tag/Set.cxx
deleted file mode 100644
index d52d517aa..000000000
--- a/src/tag/Set.cxx
+++ /dev/null
@@ -1,117 +0,0 @@
-/*
- * Copyright 2003-2017 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.
- */
-
-#include "Set.hxx"
-#include "Fallback.hxx"
-#include "TagBuilder.hxx"
-#include "util/StringView.hxx"
-
-#include <functional>
-
-#include <assert.h>
-
-/**
- * Copy all tag items of the specified type.
- */
-static bool
-CopyTagItem2(TagBuilder &dest, TagType dest_type,
-	     const Tag &src, TagType src_type)
-{
-	bool found = false;
-
-	for (const auto &item : src) {
-		if (item.type == src_type) {
-			dest.AddItem(dest_type, item.value);
-			found = true;
-		}
-	}
-
-	return found;
-}
-
-/**
- * Copy all tag items of the specified type.  Fall back to "Artist" if
- * there is no "AlbumArtist".
- */
-static void
-CopyTagItem(TagBuilder &dest, const Tag &src, TagType type)
-{
-	ApplyTagWithFallback(type,
-			     std::bind(CopyTagItem2, std::ref(dest), type,
-				       std::cref(src), std::placeholders::_1));
-}
-
-/**
- * Copy all tag items of the types in the mask.
- */
-static void
-CopyTagMask(TagBuilder &dest, const Tag &src, tag_mask_t mask)
-{
-	for (unsigned i = 0; i < TAG_NUM_OF_ITEM_TYPES; ++i)
-		if ((mask & (tag_mask_t(1) << i)) != 0)
-			CopyTagItem(dest, src, TagType(i));
-}
-
-void
-TagSet::InsertUnique(const Tag &src, TagType type, const char *value,
-		     tag_mask_t group_mask) noexcept
-{
-	TagBuilder builder;
-	builder.AddItemUnchecked(type, value);
-	CopyTagMask(builder, src, group_mask);
-#if CLANG_OR_GCC_VERSION(4,8)
-	emplace(builder.Commit());
-#else
-	insert(builder.Commit());
-#endif
-}
-
-bool
-TagSet::CheckUnique(TagType dest_type,
-		    const Tag &tag, TagType src_type,
-		    tag_mask_t group_mask) noexcept
-{
-	bool found = false;
-
-	for (const auto &item : tag) {
-		if (item.type == src_type) {
-			InsertUnique(tag, dest_type, item.value, group_mask);
-			found = true;
-		}
-	}
-
-	return found;
-}
-
-void
-TagSet::InsertUnique(const Tag &tag,
-		     TagType type, tag_mask_t group_mask) noexcept
-{
-	static_assert(sizeof(group_mask) * 8 >= TAG_NUM_OF_ITEM_TYPES,
-		      "Mask is too small");
-
-	assert((group_mask & (tag_mask_t(1) << unsigned(type))) == 0);
-
-	if (!ApplyTagWithFallback(type,
-				  std::bind(&TagSet::CheckUnique, this,
-					    type, std::cref(tag),
-					    std::placeholders::_1,
-					    group_mask)))
-		InsertUnique(tag, type, "", group_mask);
-}
diff --git a/src/tag/Set.hxx b/src/tag/Set.hxx
deleted file mode 100644
index 8e19b7ca2..000000000
--- a/src/tag/Set.hxx
+++ /dev/null
@@ -1,73 +0,0 @@
-/*
- * Copyright 2003-2017 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_TAG_SET_HXX
-#define MPD_TAG_SET_HXX
-
-#include "Compiler.h"
-#include "Tag.hxx"
-#include "Mask.hxx"
-
-#include <set>
-
-#include <string.h>
-
-/**
- * Helper class for #TagSet which compares two #Tag objects.
- */
-struct TagLess {
-	gcc_pure
-	bool operator()(const Tag &a, const Tag &b) const noexcept {
-		if (a.num_items != b.num_items)
-			return a.num_items < b.num_items;
-
-		const unsigned n = a.num_items;
-		for (unsigned i = 0; i < n; ++i) {
-			const TagItem &ai = *a.items[i];
-			const TagItem &bi = *b.items[i];
-			if (ai.type != bi.type)
-				return unsigned(ai.type) < unsigned(bi.type);
-
-			const int cmp = strcmp(ai.value, bi.value);
-			if (cmp != 0)
-				return cmp < 0;
-		}
-
-		return false;
-	}
-};
-
-/**
- * A set of #Tag objects.
- */
-class TagSet : public std::set<Tag, TagLess> {
-public:
-	void InsertUnique(const Tag &tag,
-			  TagType type, tag_mask_t group_mask) noexcept;
-
-private:
-	void InsertUnique(const Tag &src, TagType type, const char *value,
-			  tag_mask_t group_mask) noexcept;
-
-	bool CheckUnique(TagType dest_type,
-			 const Tag &tag, TagType src_type,
-			 tag_mask_t group_mask) noexcept;
-};
-
-#endif