1 files changed, 327 insertions, 0 deletions
diff --git a/absl/strings/internal/str_format/checker.h b/absl/strings/internal/str_format/checker.h
new file mode 100644
index 00000000..d0191968
--- /dev/null
+++ b/absl/strings/internal/str_format/checker.h
@@ -0,0 +1,327 @@
+#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 {
+inline namespace lts_2018_12_18 {
+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
+}  // inline namespace lts_2018_12_18
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_STR_FORMAT_CHECKER_H_