LibCMake: Add a lexer for CMakeCache.txt

This is a totally different syntax than for regular CMake files, and
also is undocumented and subject to change, but it's also nice and
simple. :^)

Userland/Libraries/LibCMake/CMakeCache/Lexer.cpp

@@ -0,0 +1,203 @@
+/*
+ * Copyright (c) 2023, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "Lexer.h"
+#include <AK/CharacterTypes.h>
+#include <AK/Debug.h>
+#include <AK/ScopeLogger.h>
+
+namespace CMake::Cache {
+
+static bool is_identifier_start_character(u32 c)
+{
+    return AK::is_ascii_alpha(c) || c == '_' || c == '-';
+}
+
+static bool is_identifier_character(u32 c)
+{
+    return AK::is_ascii_alphanumeric(c) || c == '_' || c == '-';
+}
+
+Lexer::Lexer(StringView input)
+    : GenericLexer(input)
+{
+}
+
+ErrorOr<Vector<Token>> Lexer::lex(StringView input)
+{
+    Lexer lexer { input };
+    return lexer.lex_file();
+}
+
+ErrorOr<Vector<Token>> Lexer::lex_file()
+{
+    ScopeLogger<CMAKE_DEBUG> logger;
+
+    while (!is_eof()) {
+        skip_whitespace();
+
+        if (is_eof())
+            break;
+
+        if (next_is('#')) {
+            consume_comment();
+            continue;
+        }
+
+        if (next_is("//"sv)) {
+            consume_help_text();
+            continue;
+        }
+
+        if (next_is(is_identifier_start_character)) {
+            consume_variable_definition();
+            continue;
+        }
+
+        consume_garbage();
+    }
+
+    return m_tokens;
+}
+
+void Lexer::skip_whitespace()
+{
+    ScopeLogger<CMAKE_DEBUG> log;
+
+    while (!is_eof()) {
+        if (next_is('\n')) {
+            next_line();
+            continue;
+        }
+        auto consumed = consume_while(AK::is_ascii_space);
+        if (consumed.is_empty())
+            break;
+    }
+}
+
+void Lexer::consume_comment()
+{
+    ScopeLogger<CMAKE_DEBUG> log;
+
+    auto start = position();
+    VERIFY(consume_specific('#'));
+    auto comment = consume_until('\n');
+    emit_token(Token::Type::Comment, comment, start, position());
+}
+
+void Lexer::consume_help_text()
+{
+    ScopeLogger<CMAKE_DEBUG> log;
+
+    auto start = position();
+    VERIFY(consume_specific("//"sv));
+    auto help_text = consume_until('\n');
+    emit_token(Token::Type::HelpText, help_text, start, position());
+}
+
+void Lexer::consume_variable_definition()
+{
+    ScopeLogger<CMAKE_DEBUG> log;
+
+    consume_key();
+
+    if (!next_is(':')) {
+        consume_garbage();
+        return;
+    }
+    consume_colon();
+
+    if (!next_is(is_identifier_start_character)) {
+        consume_garbage();
+        return;
+    }
+    consume_type();
+
+    if (!next_is('=')) {
+        consume_garbage();
+        return;
+    }
+    consume_equals();
+
+    consume_value();
+}
+
+void Lexer::consume_key()
+{
+    ScopeLogger<CMAKE_DEBUG> log;
+
+    auto start = position();
+    auto key = consume_while(is_identifier_character);
+    emit_token(Token::Type::Key, key, start, position());
+}
+
+void Lexer::consume_colon()
+{
+    ScopeLogger<CMAKE_DEBUG> log;
+
+    auto start = position();
+    VERIFY(consume_specific(':'));
+    emit_token(Token::Type::Colon, ":"sv, start, position());
+}
+
+void Lexer::consume_type()
+{
+    ScopeLogger<CMAKE_DEBUG> log;
+
+    auto start = position();
+    auto type = consume_while(is_identifier_character);
+    emit_token(Token::Type::Type, type, start, position());
+}
+
+void Lexer::consume_equals()
+{
+    ScopeLogger<CMAKE_DEBUG> log;
+
+    auto start = position();
+    VERIFY(consume_specific('='));
+    emit_token(Token::Type::Colon, "="sv, start, position());
+}
+
+void Lexer::consume_value()
+{
+    ScopeLogger<CMAKE_DEBUG> log;
+
+    auto start = position();
+    auto value = consume_until('\n');
+    emit_token(Token::Type::Value, value, start, position());
+}
+
+void Lexer::consume_garbage()
+{
+    ScopeLogger<CMAKE_DEBUG> log;
+
+    auto start = position();
+    auto garbage = consume_until('\n');
+    emit_token(Token::Type::Garbage, garbage, start, position());
+}
+
+Position Lexer::position() const
+{
+    return Position {
+        .line = m_line,
+        .column = tell() - m_string_offset_after_previous_newline,
+    };
+}
+
+void Lexer::next_line()
+{
+    VERIFY(consume_specific('\n'));
+    m_string_offset_after_previous_newline = tell();
+    m_line++;
+}
+
+void Lexer::emit_token(Token::Type type, StringView value, Position start, Position end)
+{
+    dbgln_if(CMAKE_DEBUG, "Emitting {} token: `{}` ({}:{} to {}:{})", to_string(type), value, start.line, start.column, end.line, end.column);
+    m_tokens.empend(type, value, start, end);
+}
+
+}