Add support for collation sequences implemented in Go.

This allows Go programs to register custom comparison functions with
sqlite, and ORDER BY that comparator.

sqlite3_test.go

@@ -1213,6 +1213,127 @@ func TestFunctionRegistration(t *testing.T) {
 	}
 }
 
+func rot13(r rune) rune {
+	switch {
+	case r >= 'A' && r <= 'Z':
+		return 'A' + (r-'A'+13)%26
+	case r >= 'a' && r <= 'z':
+		return 'a' + (r-'a'+13)%26
+	}
+	return r
+}
+
+func TestCollationRegistration(t *testing.T) {
+	collateRot13 := func(a, b string) int {
+		ra, rb := strings.Map(rot13, a), strings.Map(rot13, b)
+		return strings.Compare(ra, rb)
+	}
+	collateRot13Reverse := func(a, b string) int {
+		return collateRot13(b, a)
+	}
+
+	sql.Register("sqlite3_CollationRegistration", &SQLiteDriver{
+		ConnectHook: func(conn *SQLiteConn) error {
+			if err := conn.RegisterCollation("rot13", collateRot13); err != nil {
+				return err
+			}
+			if err := conn.RegisterCollation("rot13reverse", collateRot13Reverse); err != nil {
+				return err
+			}
+			return nil
+		},
+	})
+
+	db, err := sql.Open("sqlite3_CollationRegistration", ":memory:")
+	if err != nil {
+		t.Fatal("Failed to open database:", err)
+	}
+	defer db.Close()
+
+	populate := []string{
+		`CREATE TABLE test (s TEXT)`,
+		`INSERT INTO test VALUES ("aaaa")`,
+		`INSERT INTO test VALUES ("ffff")`,
+		`INSERT INTO test VALUES ("qqqq")`,
+		`INSERT INTO test VALUES ("tttt")`,
+		`INSERT INTO test VALUES ("zzzz")`,
+	}
+	for _, stmt := range populate {
+		if _, err := db.Exec(stmt); err != nil {
+			t.Fatal("Failed to populate test DB:", err)
+		}
+	}
+
+	ops := []struct {
+		query string
+		want  []string
+	}{
+		{
+			"SELECT * FROM test ORDER BY s COLLATE rot13 ASC",
+			[]string{
+				"qqqq",
+				"tttt",
+				"zzzz",
+				"aaaa",
+				"ffff",
+			},
+		},
+		{
+			"SELECT * FROM test ORDER BY s COLLATE rot13 DESC",
+			[]string{
+				"ffff",
+				"aaaa",
+				"zzzz",
+				"tttt",
+				"qqqq",
+			},
+		},
+		{
+			"SELECT * FROM test ORDER BY s COLLATE rot13reverse ASC",
+			[]string{
+				"ffff",
+				"aaaa",
+				"zzzz",
+				"tttt",
+				"qqqq",
+			},
+		},
+		{
+			"SELECT * FROM test ORDER BY s COLLATE rot13reverse DESC",
+			[]string{
+				"qqqq",
+				"tttt",
+				"zzzz",
+				"aaaa",
+				"ffff",
+			},
+		},
+	}
+
+	for _, op := range ops {
+		rows, err := db.Query(op.query)
+		if err != nil {
+			t.Fatalf("Query %q failed: %s", op.query, err)
+		}
+		got := []string{}
+		defer rows.Close()
+		for rows.Next() {
+			var s string
+			if err = rows.Scan(&s); err != nil {
+				t.Fatalf("Reading row for %q: %s", op.query, err)
+			}
+			got = append(got, s)
+		}
+		if err = rows.Err(); err != nil {
+			t.Fatalf("Reading rows for %q: %s", op.query, err)
+		}
+
+		if !reflect.DeepEqual(got, op.want) {
+			t.Fatalf("Unexpected output from %q\ngot:\n%s\n\nwant:\n%s", op.query, strings.Join(got, "\n"), strings.Join(op.want, "\n"))
+		}
+	}
+}
+
 func TestDeclTypes(t *testing.T) {
 
 	d := SQLiteDriver{}