ladybird/AK/CheckedFormatString.h

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/*
* Copyright (c) 2021, the SerenityOS developers.
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/AllOf.h>
#include <AK/AnyOf.h>
#include <AK/StdLibExtras.h>
#include <AK/StringView.h>
#ifdef ENABLE_COMPILETIME_FORMAT_CHECK
// FIXME: Seems like clang doesn't like calling 'consteval' functions inside 'consteval' functions quite the same way as GCC does,
// it seems to entirely forget that it accepted that parameters to a 'consteval' function to begin with.
# ifdef __clang__
# undef ENABLE_COMPILETIME_FORMAT_CHECK
# endif
#endif
#ifdef ENABLE_COMPILETIME_FORMAT_CHECK
namespace AK::Format::Detail {
// We have to define a local "purely constexpr" Array that doesn't lead back to us (via e.g. VERIFY)
template<typename T, size_t Size>
struct Array {
constexpr static size_t size() { return Size; }
constexpr const T& operator[](size_t index) const { return __data[index]; }
constexpr T& operator[](size_t index) { return __data[index]; }
using ConstIterator = SimpleIterator<const Array, const T>;
using Iterator = SimpleIterator<Array, T>;
constexpr ConstIterator begin() const { return ConstIterator::begin(*this); }
constexpr Iterator begin() { return Iterator::begin(*this); }
constexpr ConstIterator end() const { return ConstIterator::end(*this); }
constexpr Iterator end() { return Iterator::end(*this); }
T __data[Size];
};
template<typename... Args>
void compiletime_fail(Args...);
template<size_t N>
consteval auto extract_used_argument_index(const char (&fmt)[N], size_t specifier_start_index, size_t specifier_end_index, size_t& next_implicit_argument_index)
{
struct {
size_t index_value { 0 };
bool saw_explicit_index { false };
} state;
for (size_t i = specifier_start_index; i < specifier_end_index; ++i) {
auto c = fmt[i];
if (c > '9' || c < '0')
break;
state.index_value *= 10;
state.index_value += c - '0';
state.saw_explicit_index = true;
}
if (!state.saw_explicit_index)
return next_implicit_argument_index++;
return state.index_value;
}
// FIXME: We should rather parse these format strings at compile-time if possible.
template<size_t N>
consteval auto count_fmt_params(const char (&fmt)[N])
{
struct {
// FIXME: Switch to variable-sized storage whenever we can come up with one :)
Array<size_t, 128> used_arguments { 0 };
size_t total_used_argument_count { 0 };
size_t next_implicit_argument_index { 0 };
bool has_explicit_argument_references { false };
size_t unclosed_braces { 0 };
size_t extra_closed_braces { 0 };
size_t nesting_level { 0 };
Array<size_t, 4> last_format_specifier_start { 0 };
size_t total_used_last_format_specifier_start_count { 0 };
} result;
for (size_t i = 0; i < N; ++i) {
auto ch = fmt[i];
switch (ch) {
case '{':
if (i + 1 < N && fmt[i + 1] == '{') {
++i;
continue;
}
// Note: There's no compile-time throw, so we have to abuse a compile-time string to store errors.
if (result.total_used_last_format_specifier_start_count >= result.last_format_specifier_start.size() - 1)
compiletime_fail("Format-String Checker internal error: Format specifier nested too deep");
result.last_format_specifier_start[result.total_used_last_format_specifier_start_count++] = i + 1;
++result.unclosed_braces;
++result.nesting_level;
break;
case '}':
if (result.nesting_level == 0) {
if (i + 1 < N && fmt[i + 1] == '}') {
++i;
continue;
}
}
if (result.unclosed_braces) {
--result.nesting_level;
--result.unclosed_braces;
if (result.total_used_last_format_specifier_start_count == 0)
compiletime_fail("Format-String Checker internal error: Expected location information");
const auto specifier_start_index = result.last_format_specifier_start[--result.total_used_last_format_specifier_start_count];
if (result.total_used_argument_count >= result.used_arguments.size())
compiletime_fail("Format-String Checker internal error: Too many format arguments in format string");
auto used_argument_index = extract_used_argument_index<N>(fmt, specifier_start_index, i, result.next_implicit_argument_index);
if (used_argument_index + 1 != result.next_implicit_argument_index)
result.has_explicit_argument_references = true;
result.used_arguments[result.total_used_argument_count++] = used_argument_index;
} else {
++result.extra_closed_braces;
}
break;
default:
continue;
}
}
return result;
}
}
#endif
namespace AK::Format::Detail {
template<typename... Args>
struct CheckedFormatString {
template<size_t N>
consteval CheckedFormatString(const char (&fmt)[N])
: m_string { fmt }
{
#ifdef ENABLE_COMPILETIME_FORMAT_CHECK
check_format_parameter_consistency<N, sizeof...(Args)>(fmt);
#endif
}
template<typename T>
CheckedFormatString(const T& unchecked_fmt) requires(requires(T t) { StringView { t }; })
: m_string(unchecked_fmt)
{
}
auto view() const { return m_string; }
private:
#ifdef ENABLE_COMPILETIME_FORMAT_CHECK
template<size_t N, size_t param_count>
consteval static bool check_format_parameter_consistency(const char (&fmt)[N])
{
auto check = count_fmt_params<N>(fmt);
if (check.unclosed_braces != 0)
compiletime_fail("Extra unclosed braces in format string");
if (check.extra_closed_braces != 0)
compiletime_fail("Extra closing braces in format string");
{
auto begin = check.used_arguments.begin();
auto end = check.used_arguments.begin() + check.total_used_argument_count;
auto has_all_referenced_arguments = !AK::any_of(begin, end, [](auto& entry) { return entry >= param_count; });
if (!has_all_referenced_arguments)
compiletime_fail("Format string references nonexistent parameter");
}
if (!check.has_explicit_argument_references && check.total_used_argument_count != param_count)
compiletime_fail("Format string does not reference all passed parameters");
// Ensure that no passed parameter is ignored or otherwise not referenced in the format
// As this check is generally pretty expensive, try to avoid it where it cannot fail.
// We will only do this check if the format string has explicit argument refs
// otherwise, the check above covers this check too, as implicit refs
// monotonically increase, and cannot have 'gaps'.
if (check.has_explicit_argument_references) {
auto all_parameters = iota_array<size_t, param_count>(0);
constexpr auto contains = [](auto begin, auto end, auto entry) {
for (; begin != end; begin++) {
if (*begin == entry)
return true;
}
return false;
};
auto references_all_arguments = AK::all_of(
all_parameters.begin(),
all_parameters.end(),
[&](auto& entry) {
return contains(
check.used_arguments.begin(),
check.used_arguments.begin() + check.total_used_argument_count,
entry);
});
if (!references_all_arguments)
compiletime_fail("Format string does not reference all passed parameters");
}
return true;
}
#endif
StringView m_string;
};
}
namespace AK {
template<typename... Args>
using CheckedFormatString = Format::Detail::CheckedFormatString<IdentityType<Args>...>;
}