lib: implement new query parser

mu's query parser is the piece of software that turns your queries
into something the Xapian database can understand. So, if you query
"maildir:/inbox and subject:bla" this must be translated into a
Xapian::Query object which will retrieve the sought after messages.

Since mu's beginning, almost a decade ago, this parser was based on
Xapian's default Xapian::QueryParser. It works okay, but wasn't really
designed for the mu use-case, and had a bit of trouble with anything
that's not A..Z (think: spaces, special characters, unicode etc.).

Over the years, mu added quite a bit of pre-processing trickery to
deal with that. Still, there were corner cases and bugs that were
practically unfixable.

The solution to all of this is to have a custom query processor that
replaces Xapian's, and write it from the ground up to deal with the
special characters etc. I wrote one, as part of my "future, post-1.0
mu" reseach project, and I have now backported it to the mu 0.9.19.

From a technical perspective, this is a major cleanup, and allows us
to get rid of much of the fragile preprocessing both for indexing and
querying. From and end-user perspective this (hopefully) means that
many of the little parsing issues are gone, and it opens the way for
some new features.

From an end-user perspective:
- better support for special characters.
- regexp search! yes, you can now search for regular expressions, e.g.
      subject:/h.ll?o/
  will find subjects with hallo, hello, halo,  philosophy, ...

  As you can imagine, this can be a _heavy_ operation on the database,
  and might take quite a bit longer than a normal query; but it can be
  quite useful.

lib/parser/test-parser.cc

@@ -0,0 +1,121 @@
+/*
+** Copyright (C) 2017 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
+**
+**  This library is free software; you can redistribute it and/or
+**  modify it under the terms of the GNU Lesser General Public License
+**  as published by the Free Software Foundation; either version 2.1
+**  of the License, or (at your option) any later version.
+**
+**  This library 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
+**  Lesser General Public License for more details.
+**
+**  You should have received a copy of the GNU Lesser General Public
+**  License along with this library; if not, write to the Free
+**  Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
+**  02110-1301, USA.
+*/
+
+#include <vector>
+#include <glib.h>
+
+#include <iostream>
+#include <sstream>
+
+#include "parser.hh"
+using namespace Mux;
+
+struct Case {
+	const std::string expr;
+	const std::string expected;
+	WarningVec warnings;
+};
+
+using CaseVec = std::vector<Case>;
+
+static void
+test_cases(const CaseVec& cases)
+{
+	for (const auto& casus : cases ) {
+
+		WarningVec warnings;
+		const auto tree = parse (casus.expr, warnings);
+
+		std::stringstream ss;
+		ss << tree;
+
+		if (g_test_verbose()) {
+			std::cout << "\n";
+			std::cout << casus.expr << std::endl;
+			std::cout << "exp:" << casus.expected << std::endl;
+			std::cout << "got:" << ss.str() << std::endl;
+		}
+		g_assert_true (casus.expected == ss.str());
+
+		// g_assert_cmpuint (casus.warnings.size(), ==, warnings.size());
+		// for (auto i = 0; i != (int)casus.warnings.size(); ++i) {
+		// 	std::cout << "exp:" << casus.warnings[i] << std::endl;
+		// 	std::cout << "got:" << warnings[i] << std::endl;
+		// 	g_assert_true (casus.warnings[i] == warnings[i]);
+		// }
+	}
+}
+
+static void
+test_basic ()
+{
+	CaseVec cases = {
+		//{ "", R"#((atom :value ""))#"},
+		{ "foo",  R"#((value "" "foo"))#", },
+		{ "foo       or         bar",
+		  R"#((or(value "" "foo")(value "" "bar")))#" },
+		{ "foo and bar",
+		  R"#((and(value "" "foo")(value "" "bar")))#"},
+	};
+
+	test_cases (cases);
+}
+
+static void
+test_complex ()
+{
+	CaseVec cases = {
+		{ "foo and bar or cuux",
+		  R"#((or(and(value "" "foo")(value "" "bar")))#" +
+		  std::string(R"#((value "" "cuux")))#") },
+		{ "a and not b",
+		  R"#((andnot(value "" "a")(value "" "b")))#"
+		},
+		{ "a and b and c",
+		  R"#((and(value "" "a")(and(value "" "b")(value "" "c"))))#"
+		},
+		{ "(a or b) and c",
+		  R"#((and(or(value "" "a")(value "" "b"))(value "" "c")))#"
+		}
+	};
+
+	test_cases (cases);
+}
+
+static void
+test_flatten ()
+{
+	CaseVec cases = {
+		{ " Mötørhęåđ", R"#((value "" "motorhead"))#" }
+	};
+
+	test_cases (cases);
+}
+
+int
+main (int argc, char *argv[])
+{
+	g_test_init (&argc, &argv, NULL);
+
+	g_test_add_func ("/parser/basic",    test_basic);
+	g_test_add_func ("/parser/complex",  test_complex);
+	g_test_add_func ("/parser/flatten",  test_flatten);
+
+	return g_test_run ();
+}