SongFilter: add special keyword "base"

Restores the features from the previous draft commands "findin" /
"searchin".

NEWS

@@ -6,6 +6,7 @@ ver 0.18 (2012/??/??)
   - new command "readcomments" lists arbitrary file tags
   - new command "toggleoutput"
   - "find"/"search" with "any" does not match file name
+  - "search" and "find" with base URI (keyword "base")
   - search for album artist falls back to the artist tag
   - re-add the "volume" command
 * input:

doc/protocol.xml

@@ -1483,9 +1483,13 @@ OK
             <para>
               Finds songs in the db that are exactly
               <varname>WHAT</varname>.  <varname>TYPE</varname> can
-              be any tag supported by MPD, or one of the two special
+              be any tag supported by MPD, or one of the three special
               parameters — <parameter>file</parameter> to search by
-              full path (relative to database root), and
+
+              full path (relative to the music directory),
+              <parameter>in</parameter> to restrict the search to
+              songs in the given directory (also relative to the music
+              directory) and
               <parameter>any</parameter> to match against all
               available tags.  <varname>WHAT</varname> is what to find.
             </para>

src/DatabaseSelection.cxx

@@ -20,6 +20,16 @@
 #include "DatabaseSelection.hxx"
 #include "SongFilter.hxx"
 
+DatabaseSelection::DatabaseSelection(const char *_uri, bool _recursive,
+				     const SongFilter *_filter)
+	:uri(_uri), recursive(_recursive), filter(_filter)
+{
+	/* optimization: if the caller didn't specify a base URI, pick
+	   the one from SongFilter */
+	if (uri.empty() && filter != nullptr)
+		uri = filter->GetBase();
+}
+
 bool
 DatabaseSelection::Match(const Song &song) const
 {

src/DatabaseSelection.hxx

@@ -42,9 +42,7 @@ struct DatabaseSelection {
 	const SongFilter *filter;
 
 	DatabaseSelection(const char *_uri, bool _recursive,
-			  const SongFilter *_filter=nullptr)
-		:uri(_uri), recursive(_recursive), filter(_filter) {
-	}
+			  const SongFilter *_filter=nullptr);
 
 	gcc_pure
 	bool Match(const Song &song) const;

src/SongFilter.cxx

@@ -22,6 +22,7 @@
 #include "Song.hxx"
 #include "tag/Tag.hxx"
 #include "util/ASCII.hxx"
+#include "util/UriUtil.hxx"
 
 #include <glib.h>
 
@@ -43,6 +44,9 @@ locate_parse_type(const char *str)
 	if (StringEqualsCaseASCII(str, LOCATE_TAG_ANY_KEY))
 		return LOCATE_TAG_ANY_TYPE;
 
+	if (strcmp(str, "base") == 0)
+		return LOCATE_TAG_BASE_TYPE;
+
 	return tag_name_parse_i(str);
 }
 
@@ -134,6 +138,11 @@ SongFilter::Item::Match(const Tag &_tag) const
 bool
 SongFilter::Item::Match(const Song &song) const
 {
+	if (tag == LOCATE_TAG_BASE_TYPE) {
+		const auto uri = song.GetURI();
+		return uri_is_child_or_same(value.c_str(), uri.c_str());
+	}
+
 	if (tag == LOCATE_TAG_FILE_TYPE) {
 		const auto uri = song.GetURI();
 		return StringMatch(uri.c_str());
@@ -159,6 +168,14 @@ SongFilter::Parse(const char *tag_string, const char *value, bool fold_case)
 	if (tag == TAG_NUM_OF_ITEM_TYPES)
 		return false;
 
+	if (tag == LOCATE_TAG_BASE_TYPE) {
+		if (!uri_safe_local(value))
+			return false;
+
+		/* case folding doesn't work with "base" */
+		fold_case = false;
+	}
+
 	items.push_back(Item(tag, value, fold_case));
 	return true;
 }
@@ -185,3 +202,13 @@ SongFilter::Match(const Song &song) const
 
 	return true;
 }
+
+std::string
+SongFilter::GetBase() const
+{
+	for (const auto &i : items)
+		if (i.GetTag() == LOCATE_TAG_BASE_TYPE)
+			return i.GetValue();
+
+	return std::string();
+}

src/SongFilter.hxx

@@ -27,6 +27,11 @@
 
 #include <stdint.h>
 
+/**
+ * Limit the search to files within the given directory.
+ */
+#define LOCATE_TAG_BASE_TYPE (TAG_NUM_OF_ITEM_TYPES + 1)
+
 #define LOCATE_TAG_FILE_TYPE	TAG_NUM_OF_ITEM_TYPES+10
 #define LOCATE_TAG_ANY_TYPE     TAG_NUM_OF_ITEM_TYPES+20
 
@@ -99,6 +104,13 @@ public:
 	const std::list<Item> &GetItems() const {
 		return items;
 	}
+
+	/**
+	 * Returns the "base" specification (if there is one) or an
+	 * empty string.
+	 */
+	gcc_pure
+	std::string GetBase() const;
 };
 
 /**