LibJS: Add Javascript lexer and parser

This adds a basic Javascript lexer and parser. It can parse the
currently existing demo programs. More work needs to be done to
turn it into a complete parser than can parse arbitrary JS Code.

The lexer outputs tokens with preceeding whitespace and comments
in the trivia member. This should allow us to generate the exact
source code by concatenating the generated tokens.

The parser is written in a way that it always returns a complete
syntax tree. Error conditions are represented as nodes in the
tree. This simplifies the code and allows it to be used as an
early stage parser, e.g for parsing JS documents in an IDE while
editing the source code.:

1 files changed, 61 insertions, 0 deletions

diff --git a/Libraries/LibJS/Lexer.h b/Libraries/LibJS/Lexer.h
new file mode 100644
index 0000000000..01d1fdc1ce
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+++ b/Libraries/LibJS/Lexer.h
@@ -0,0 +1,61 @@
+/*
+ * Copyright (c) 2020, Stephan Unverwerth <s.unverwerth@gmx.de>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "Token.h"
+
+#include <AK/HashMap.h>
+#include <AK/String.h>
+#include <AK/StringView.h>
+
+namespace JS {
+
+class Lexer {
+public:
+    explicit Lexer(StringView source);
+    Token next();
+
+private:
+    void consume();
+    bool is_eof() const;
+    bool is_identifier_start() const;
+    bool is_identifier_middle() const;
+    bool is_line_comment_start() const;
+    bool is_block_comment_start() const;
+    bool is_block_comment_end() const;
+
+    StringView m_source;
+    size_t m_position = 0;
+    Token m_current_token;
+    int m_current_char;
+
+    static HashMap<String, TokenType> s_keywords;
+    static HashMap<String, TokenType> s_two_char_tokens;
+    static HashMap<char, TokenType> s_single_char_tokens;
+};
+
+}