--- /dev/null
+#ifndef ABSL_STRINGS_INTERNAL_STR_FORMAT_CHECKER_H_
+#define ABSL_STRINGS_INTERNAL_STR_FORMAT_CHECKER_H_
+
+#include "absl/strings/internal/str_format/arg.h"
+#include "absl/strings/internal/str_format/extension.h"
+
+// Compile time check support for entry points.
+
+#ifndef ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
+#if defined(__clang__) && !defined(__native_client__)
+#if __has_attribute(enable_if)
+#define ABSL_INTERNAL_ENABLE_FORMAT_CHECKER 1
+#endif // __has_attribute(enable_if)
+#endif // defined(__clang__) && !defined(__native_client__)
+#endif // ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
+
+namespace absl {
+namespace str_format_internal {
+
+constexpr bool AllOf() { return true; }
+
+template <typename... T>
+constexpr bool AllOf(bool b, T... t) {
+ return b && AllOf(t...);
+}
+
+template <typename Arg>
+constexpr Conv ArgumentToConv() {
+ return decltype(str_format_internal::FormatConvertImpl(
+ std::declval<const Arg&>(), std::declval<const ConversionSpec&>(),
+ std::declval<FormatSinkImpl*>()))::kConv;
+}
+
+#if ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
+
+constexpr bool ContainsChar(const char* chars, char c) {
+ return *chars == c || (*chars && ContainsChar(chars + 1, c));
+}
+
+// A constexpr compatible list of Convs.
+struct ConvList {
+ const Conv* array;
+ int count;
+
+ // We do the bound check here to avoid having to do it on the callers.
+ // Returning an empty Conv has the same effect as short circuiting because it
+ // will never match any conversion.
+ constexpr Conv operator[](int i) const {
+ return i < count ? array[i] : Conv{};
+ }
+
+ constexpr ConvList without_front() const {
+ return count != 0 ? ConvList{array + 1, count - 1} : *this;
+ }
+};
+
+template <size_t count>
+struct ConvListT {
+ // Make sure the array has size > 0.
+ Conv list[count ? count : 1];
+};
+
+constexpr char GetChar(string_view str, size_t index) {
+ return index < str.size() ? str[index] : char{};
+}
+
+constexpr string_view ConsumeFront(string_view str, size_t len = 1) {
+ return len <= str.size() ? string_view(str.data() + len, str.size() - len)
+ : string_view();
+}
+
+constexpr string_view ConsumeAnyOf(string_view format, const char* chars) {
+ return ContainsChar(chars, GetChar(format, 0))
+ ? ConsumeAnyOf(ConsumeFront(format), chars)
+ : format;
+}
+
+constexpr bool IsDigit(char c) { return c >= '0' && c <= '9'; }
+
+// Helper class for the ParseDigits function.
+// It encapsulates the two return values we need there.
+struct Integer {
+ string_view format;
+ int value;
+
+ // If the next character is a '$', consume it.
+ // Otherwise, make `this` an invalid positional argument.
+ constexpr Integer ConsumePositionalDollar() const {
+ return GetChar(format, 0) == '$' ? Integer{ConsumeFront(format), value}
+ : Integer{format, 0};
+ }
+};
+
+constexpr Integer ParseDigits(string_view format, int value = 0) {
+ return IsDigit(GetChar(format, 0))
+ ? ParseDigits(ConsumeFront(format),
+ 10 * value + GetChar(format, 0) - '0')
+ : Integer{format, value};
+}
+
+// Parse digits for a positional argument.
+// The parsing also consumes the '$'.
+constexpr Integer ParsePositional(string_view format) {
+ return ParseDigits(format).ConsumePositionalDollar();
+}
+
+// Parses a single conversion specifier.
+// See ConvParser::Run() for post conditions.
+class ConvParser {
+ constexpr ConvParser SetFormat(string_view format) const {
+ return ConvParser(format, args_, error_, arg_position_, is_positional_);
+ }
+
+ constexpr ConvParser SetArgs(ConvList args) const {
+ return ConvParser(format_, args, error_, arg_position_, is_positional_);
+ }
+
+ constexpr ConvParser SetError(bool error) const {
+ return ConvParser(format_, args_, error_ || error, arg_position_,
+ is_positional_);
+ }
+
+ constexpr ConvParser SetArgPosition(int arg_position) const {
+ return ConvParser(format_, args_, error_, arg_position, is_positional_);
+ }
+
+ // Consumes the next arg and verifies that it matches `conv`.
+ // `error_` is set if there is no next arg or if it doesn't match `conv`.
+ constexpr ConvParser ConsumeNextArg(char conv) const {
+ return SetArgs(args_.without_front()).SetError(!Contains(args_[0], conv));
+ }
+
+ // Verify that positional argument `i.value` matches `conv`.
+ // `error_` is set if `i.value` is not a valid argument or if it doesn't
+ // match.
+ constexpr ConvParser VerifyPositional(Integer i, char conv) const {
+ return SetFormat(i.format).SetError(!Contains(args_[i.value - 1], conv));
+ }
+
+ // Parse the position of the arg and store it in `arg_position_`.
+ constexpr ConvParser ParseArgPosition(Integer arg) const {
+ return SetFormat(arg.format).SetArgPosition(arg.value);
+ }
+
+ // Consume the flags.
+ constexpr ConvParser ParseFlags() const {
+ return SetFormat(ConsumeAnyOf(format_, "-+ #0"));
+ }
+
+ // Consume the width.
+ // If it is '*', we verify that it matches `args_`. `error_` is set if it
+ // doesn't match.
+ constexpr ConvParser ParseWidth() const {
+ return IsDigit(GetChar(format_, 0))
+ ? SetFormat(ParseDigits(format_).format)
+ : GetChar(format_, 0) == '*'
+ ? is_positional_
+ ? VerifyPositional(
+ ParsePositional(ConsumeFront(format_)), '*')
+ : SetFormat(ConsumeFront(format_))
+ .ConsumeNextArg('*')
+ : *this;
+ }
+
+ // Consume the precision.
+ // If it is '*', we verify that it matches `args_`. `error_` is set if it
+ // doesn't match.
+ constexpr ConvParser ParsePrecision() const {
+ return GetChar(format_, 0) != '.'
+ ? *this
+ : GetChar(format_, 1) == '*'
+ ? is_positional_
+ ? VerifyPositional(
+ ParsePositional(ConsumeFront(format_, 2)), '*')
+ : SetFormat(ConsumeFront(format_, 2))
+ .ConsumeNextArg('*')
+ : SetFormat(ParseDigits(ConsumeFront(format_)).format);
+ }
+
+ // Consume the length characters.
+ constexpr ConvParser ParseLength() const {
+ return SetFormat(ConsumeAnyOf(format_, "lLhjztq"));
+ }
+
+ // Consume the conversion character and verify that it matches `args_`.
+ // `error_` is set if it doesn't match.
+ constexpr ConvParser ParseConversion() const {
+ return is_positional_
+ ? VerifyPositional({ConsumeFront(format_), arg_position_},
+ GetChar(format_, 0))
+ : ConsumeNextArg(GetChar(format_, 0))
+ .SetFormat(ConsumeFront(format_));
+ }
+
+ constexpr ConvParser(string_view format, ConvList args, bool error,
+ int arg_position, bool is_positional)
+ : format_(format),
+ args_(args),
+ error_(error),
+ arg_position_(arg_position),
+ is_positional_(is_positional) {}
+
+ public:
+ constexpr ConvParser(string_view format, ConvList args, bool is_positional)
+ : format_(format),
+ args_(args),
+ error_(false),
+ arg_position_(0),
+ is_positional_(is_positional) {}
+
+ // Consume the whole conversion specifier.
+ // `format()` will be set to the character after the conversion character.
+ // `error()` will be set if any of the arguments do not match.
+ constexpr ConvParser Run() const {
+ return (is_positional_ ? ParseArgPosition(ParsePositional(format_)) : *this)
+ .ParseFlags()
+ .ParseWidth()
+ .ParsePrecision()
+ .ParseLength()
+ .ParseConversion();
+ }
+
+ constexpr string_view format() const { return format_; }
+ constexpr ConvList args() const { return args_; }
+ constexpr bool error() const { return error_; }
+ constexpr bool is_positional() const { return is_positional_; }
+
+ private:
+ string_view format_;
+ // Current list of arguments. If we are not in positional mode we will consume
+ // from the front.
+ ConvList args_;
+ bool error_;
+ // Holds the argument position of the conversion character, if we are in
+ // positional mode. Otherwise, it is unspecified.
+ int arg_position_;
+ // Whether we are in positional mode.
+ // It changes the behavior of '*' and where to find the converted argument.
+ bool is_positional_;
+};
+
+// Parses a whole format expression.
+// See FormatParser::Run().
+class FormatParser {
+ static constexpr bool FoundPercent(string_view format) {
+ return format.empty() ||
+ (GetChar(format, 0) == '%' && GetChar(format, 1) != '%');
+ }
+
+ // We use an inner function to increase the recursion limit.
+ // The inner function consumes up to `limit` characters on every run.
+ // This increases the limit from 512 to ~512*limit.
+ static constexpr string_view ConsumeNonPercentInner(string_view format,
+ int limit = 20) {
+ return FoundPercent(format) || !limit
+ ? format
+ : ConsumeNonPercentInner(
+ ConsumeFront(format, GetChar(format, 0) == '%' &&
+ GetChar(format, 1) == '%'
+ ? 2
+ : 1),
+ limit - 1);
+ }
+
+ // Consume characters until the next conversion spec %.
+ // It skips %%.
+ static constexpr string_view ConsumeNonPercent(string_view format) {
+ return FoundPercent(format)
+ ? format
+ : ConsumeNonPercent(ConsumeNonPercentInner(format));
+ }
+
+ static constexpr bool IsPositional(string_view format) {
+ return IsDigit(GetChar(format, 0)) ? IsPositional(ConsumeFront(format))
+ : GetChar(format, 0) == '$';
+ }
+
+ constexpr bool RunImpl(bool is_positional) const {
+ // In non-positional mode we require all arguments to be consumed.
+ // In positional mode just reaching the end of the format without errors is
+ // enough.
+ return (format_.empty() && (is_positional || args_.count == 0)) ||
+ (!format_.empty() &&
+ ValidateArg(
+ ConvParser(ConsumeFront(format_), args_, is_positional).Run()));
+ }
+
+ constexpr bool ValidateArg(ConvParser conv) const {
+ return !conv.error() && FormatParser(conv.format(), conv.args())
+ .RunImpl(conv.is_positional());
+ }
+
+ public:
+ constexpr FormatParser(string_view format, ConvList args)
+ : format_(ConsumeNonPercent(format)), args_(args) {}
+
+ // Runs the parser for `format` and `args`.
+ // It verifies that the format is valid and that all conversion specifiers
+ // match the arguments passed.
+ // In non-positional mode it also verfies that all arguments are consumed.
+ constexpr bool Run() const {
+ return RunImpl(!format_.empty() && IsPositional(ConsumeFront(format_)));
+ }
+
+ private:
+ string_view format_;
+ // Current list of arguments.
+ // If we are not in positional mode we will consume from the front and will
+ // have to be empty in the end.
+ ConvList args_;
+};
+
+template <Conv... C>
+constexpr bool ValidFormatImpl(string_view format) {
+ return FormatParser(format,
+ {ConvListT<sizeof...(C)>{{C...}}.list, sizeof...(C)})
+ .Run();
+}
+
+#endif // ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
+
+} // namespace str_format_internal
+} // namespace absl
+
+#endif // ABSL_STRINGS_INTERNAL_STR_FORMAT_CHECKER_H_
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