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AK/GenericLexer: constexpr where possible

Problem:
- Much of the `GenericLexer` can be `constexpr`, but is not.

Solution:
- Make it `constexpr` and de-duplicate code.
- Extend some of `StringView` with `constexpr` to support.
- Add tests to ensure `constexpr` behavior.

Note:
- Construction of `StringView` from pointer and length is not
  `constexpr`-compatible at the moment because the VERIFY cannot be,
  yet.
This commit is contained in:
Lenny Maiorani 2021-04-21 21:19:39 -06:00 committed by Linus Groh
parent c2280a907d
commit 254e010c75
6 changed files with 303 additions and 188 deletions

View file

@ -12,29 +12,95 @@ namespace AK {
class GenericLexer {
public:
explicit GenericLexer(const StringView& input);
virtual ~GenericLexer();
constexpr explicit GenericLexer(const StringView& input)
: m_input(input)
{
}
size_t tell() const { return m_index; }
size_t tell_remaining() const { return m_input.length() - m_index; }
constexpr size_t tell() const { return m_index; }
constexpr size_t tell_remaining() const { return m_input.length() - m_index; }
StringView remaining() const { return m_input.substring_view(m_index); }
bool is_eof() const;
constexpr bool is_eof() const { return m_index >= m_input.length(); }
char peek(size_t offset = 0) const;
constexpr char peek(size_t offset = 0) const
{
return (m_index + offset < m_input.length()) ? m_input[m_index + offset] : '\0';
}
bool next_is(char) const;
bool next_is(StringView) const;
bool next_is(const char*) const;
constexpr bool next_is(char expected) const
{
return peek() == expected;
}
void retreat();
constexpr bool next_is(StringView expected) const
{
for (size_t i = 0; i < expected.length(); ++i)
if (peek(i) != expected[i])
return false;
return true;
}
constexpr bool next_is(const char* expected) const
{
for (size_t i = 0; expected[i] != '\0'; ++i)
if (peek(i) != expected[i])
return false;
return true;
}
constexpr void retreat()
{
VERIFY(m_index > 0);
--m_index;
}
constexpr char consume()
{
VERIFY(!is_eof());
return m_input[m_index++];
}
template<typename T>
constexpr bool consume_specific(const T& next)
{
if (!next_is(next))
return false;
if constexpr (requires { next.length(); }) {
ignore(next.length());
} else {
ignore(sizeof(next));
}
return true;
}
bool consume_specific(const String& next)
{
return consume_specific(StringView { next });
}
constexpr bool consume_specific(const char* next)
{
return consume_specific(StringView { next });
}
constexpr char consume_escaped_character(char escape_char = '\\', const StringView& escape_map = "n\nr\rt\tb\bf\f")
{
if (!consume_specific(escape_char))
return consume();
auto c = consume();
for (size_t i = 0; i < escape_map.length(); i += 2) {
if (c == escape_map[i])
return escape_map[i + 1];
}
return c;
}
char consume();
bool consume_specific(char);
bool consume_specific(StringView);
bool consume_specific(const char*);
char consume_escaped_character(char escape_char = '\\', const StringView& escape_map = "n\nr\rt\tb\bf\f");
StringView consume(size_t count);
StringView consume_all();
StringView consume_line();
@ -43,9 +109,27 @@ public:
StringView consume_quoted_string(char escape_char = 0);
String consume_and_unescape_string(char escape_char = '\\');
void ignore(size_t count = 1);
void ignore_until(char);
void ignore_until(const char*);
constexpr void ignore(size_t count = 1)
{
count = min(count, m_input.length() - m_index);
m_index += count;
}
constexpr void ignore_until(char stop)
{
while (!is_eof() && peek() != stop) {
++m_index;
}
ignore();
}
constexpr void ignore_until(const char* stop)
{
while (!is_eof() && !next_is(stop)) {
++m_index;
}
ignore(__builtin_strlen(stop));
}
/*
* Conditions are used to match arbitrary characters. You can use lambdas,
@ -57,19 +141,19 @@ public:
*/
// Test the next character against a Condition
template<typename C>
bool next_is(C condition) const
template<typename TPredicate>
constexpr bool next_is(TPredicate pred) const
{
return condition(peek());
return pred(peek());
}
// Consume and return characters while `condition` returns true
template<typename C>
StringView consume_while(C condition)
// Consume and return characters while `pred` returns true
template<typename TPredicate>
StringView consume_while(TPredicate pred)
{
size_t start = m_index;
while (!is_eof() && condition(peek()))
m_index++;
while (!is_eof() && pred(peek()))
++m_index;
size_t length = m_index - start;
if (length == 0)
@ -77,13 +161,13 @@ public:
return m_input.substring_view(start, length);
}
// Consume and return characters until `condition` return true
template<typename C>
StringView consume_until(C condition)
// Consume and return characters until `pred` return true
template<typename TPredicate>
StringView consume_until(TPredicate pred)
{
size_t start = m_index;
while (!is_eof() && !condition(peek()))
m_index++;
while (!is_eof() && !pred(peek()))
++m_index;
size_t length = m_index - start;
if (length == 0)
@ -91,21 +175,21 @@ public:
return m_input.substring_view(start, length);
}
// Ignore characters while `condition` returns true
template<typename C>
void ignore_while(C condition)
// Ignore characters while `pred` returns true
template<typename TPredicate>
constexpr void ignore_while(TPredicate pred)
{
while (!is_eof() && condition(peek()))
m_index++;
while (!is_eof() && pred(peek()))
++m_index;
}
// Ignore characters until `condition` return true
// Ignore characters until `pred` return true
// We don't skip the stop character as it may not be a unique value
template<typename C>
void ignore_until(C condition)
template<typename TPredicate>
constexpr void ignore_until(TPredicate pred)
{
while (!is_eof() && !condition(peek()))
m_index++;
while (!is_eof() && !pred(peek()))
++m_index;
}
protected: