tree 388a184094676d8867a584848e87192e6edfa419
parent bf3a11997dbcbc6fc44924ec515fcfc582588d45
author bnc <bnc@google.com> 1652445548 -0700
committer Copybara-Service <copybara-worker@google.com> 1652445673 -0700

Add using directives to BalsaHeader to fix gcc compile error.

Three ConstHeaderApi virtual methods each have two overloads that only differ in
a single argument type: absl::string_view versus QuicheLowerCaseString.  In
Envoy, QuicheLowerCaseString is an alias to Envoy::Http::LowerCaseString [1],
which has an implicit conversion operator to absl::string_view [2].

[1]
https://github.com/envoyproxy/envoy/blob/741b8c08d3de1650fc45d5c9a75e418867a10fa9/source/common/quic/platform/quiche_lower_case_string_impl.h#L13
[2]
https://github.com/envoyproxy/envoy/blob/741b8c08d3de1650fc45d5c9a75e418867a10fa9/envoy/http/header_map.h#L82-L83

ConstHeaderApi provides a trivial definition to the QuicheLowerCaseString
overload that calls the absl::string_view overload, which is overridden in
BalsaHeaders.  This makes perfect sense but makes gcc in Envoy unhappy:

quiche/common/balsa/header_api.h:89:23: error:
‘virtual std::string quiche::ConstHeaderApi::GetAllOfHeaderAsString(const QuicheLowerCaseString&) const’ was hidden [-Werror=overloaded-virtual]
quiche/common/balsa/balsa_headers.h:560:15: error:
by ‘virtual std::string quiche::BalsaHeaders::GetAllOfHeaderAsString(absl::string_view) const’ [-Werror=overloaded-virtual]

This is because when called with a QuicheLowerCaseString argument on a
BalsaHeaders object, the latter overload is preferred over the former (due to
the implicit conversion), which is not the intended behavior.

GetAllOfHeader() does not pose an issue due to the
  using HeaderApi::GetAllOfHeader;
directive at balsa_headers.h:549.

This CL adds similar using directives to the other two methods to solve this
problem.

And here is a minimal example to verify this behavior.  Running with
gcc a.cc -Woverloaded-virtual -l:libstdc++.a && ./a.out
prints "right" and no warning, but if the using directive is removed, the
warning appears and "wrong" is printed:

#include <iostream>

class T {
 public:
  operator int() const { return 0; }
};

class base {
 public:
  virtual void print(int a) = 0;
  virtual void print(T a) { std::cout << "right" << std::endl; }
};

class derived : public base {
 public:
  using base::print;
  void print(int a) override { std::cout << "wrong" << std::endl; }
};

int main() {
  T t;
  derived c;
  c.print(t);
  return 0;
}

PiperOrigin-RevId: 448474666