Fix ostream support in sprintf (#1631)

include/fmt/core.h

@@ -830,7 +830,8 @@ template <typename Char> struct string_value {
 template <typename Context> struct custom_value {
   using parse_context = basic_format_parse_context<typename Context::char_type>;
   const void* value;
-  void (*format)(const void* arg, parse_context& parse_ctx, Context& ctx);
+  void (*format)(const void* arg,
+                 typename Context::parse_context_type& parse_ctx, Context& ctx);
 };
 
 // A formatting argument value.
@@ -890,9 +891,9 @@ template <typename Context> class value {
  private:
   // Formats an argument of a custom type, such as a user-defined class.
   template <typename T, typename Formatter>
-  static void format_custom_arg(
-      const void* arg, basic_format_parse_context<char_type>& parse_ctx,
-      Context& ctx) {
+  static void format_custom_arg(const void* arg,
+                                typename Context::parse_context_type& parse_ctx,
+                                Context& ctx) {
     Formatter f;
     parse_ctx.advance_to(f.parse(parse_ctx));
     ctx.advance_to(f.format(*static_cast<const T*>(arg), ctx));
@@ -1061,7 +1062,7 @@ template <typename Context> class basic_format_arg {
    public:
     explicit handle(internal::custom_value<Context> custom) : custom_(custom) {}
 
-    void format(basic_format_parse_context<char_type>& parse_ctx,
+    void format(typename Context::parse_context_type& parse_ctx,
                 Context& ctx) const {
       custom_.format(custom_.value, parse_ctx, ctx);
     }
@@ -1272,6 +1273,7 @@ template <typename OutputIt, typename Char> class basic_format_context {
  public:
   using iterator = OutputIt;
   using format_arg = basic_format_arg<basic_format_context>;
+  using parse_context_type = basic_format_parse_context<Char>;
   template <typename T> using formatter_type = formatter<T, char_type>;
 
   basic_format_context(const basic_format_context&) = delete;

include/fmt/ostream.h

@@ -9,9 +9,14 @@
 #define FMT_OSTREAM_H_
 
 #include <ostream>
+
 #include "format.h"
 
 FMT_BEGIN_NAMESPACE
+
+template <typename CHar> class basic_printf_parse_context;
+template <typename OutputIt, typename Char> class basic_printf_context;
+
 namespace internal {
 
 template <class Char> class formatbuf : public std::basic_streambuf<Char> {
@@ -93,9 +98,9 @@ void format_value(buffer<Char>& buf, const T& value,
                   locale_ref loc = locale_ref()) {
   formatbuf<Char> format_buf(buf);
   std::basic_ostream<Char> output(&format_buf);
-  #if !defined(FMT_STATIC_THOUSANDS_SEPARATOR)
+#if !defined(FMT_STATIC_THOUSANDS_SEPARATOR)
   if (loc) output.imbue(loc.get<std::locale>());
-  #endif
+#endif
   output.exceptions(std::ios_base::failbit | std::ios_base::badbit);
   output << value;
   buf.resize(buf.size());
@@ -104,14 +109,32 @@ void format_value(buffer<Char>& buf, const T& value,
 // Formats an object of type T that has an overloaded ostream operator<<.
 template <typename T, typename Char>
 struct fallback_formatter<T, Char, enable_if_t<is_streamable<T, Char>::value>>
-    : formatter<basic_string_view<Char>, Char> {
-  template <typename Context>
-  auto format(const T& value, Context& ctx) -> decltype(ctx.out()) {
+    : private formatter<basic_string_view<Char>, Char> {
+  auto parse(basic_format_parse_context<Char>& ctx) -> decltype(ctx.begin()) {
+    return formatter<basic_string_view<Char>, Char>::parse(ctx);
+  }
+  template <typename ParseCtx,
+            FMT_ENABLE_IF(std::is_same<
+                          ParseCtx, basic_printf_parse_context<Char>>::value)>
+  auto parse(ParseCtx& ctx) -> decltype(ctx.begin()) {
+    return ctx.begin();
+  }
+
+  template <typename OutputIt>
+  auto format(const T& value, basic_format_context<OutputIt, Char>& ctx)
+      -> OutputIt {
     basic_memory_buffer<Char> buffer;
     format_value(buffer, value, ctx.locale());
     basic_string_view<Char> str(buffer.data(), buffer.size());
     return formatter<basic_string_view<Char>, Char>::format(str, ctx);
   }
+  template <typename OutputIt>
+  auto format(const T& value, basic_printf_context<OutputIt, Char>& ctx)
+      -> OutputIt {
+    basic_memory_buffer<Char> buffer;
+    format_value(buffer, value, ctx.locale());
+    return std::copy(buffer.begin(), buffer.end(), ctx.out());
+  }
 };
 }  // namespace internal
 

include/fmt/printf.h

@@ -189,6 +189,10 @@ using internal::printf;  // For printing into memory_buffer.
 
 template <typename Range> class printf_arg_formatter;
 
+template <typename Char>
+class basic_printf_parse_context : public basic_format_parse_context<Char> {
+  using basic_format_parse_context<Char>::basic_format_parse_context;
+};
 template <typename OutputIt, typename Char> class basic_printf_context;
 
 /**
@@ -324,6 +328,7 @@ template <typename OutputIt, typename Char> class basic_printf_context {
   using char_type = Char;
   using iterator = OutputIt;
   using format_arg = basic_format_arg<basic_printf_context>;
+  using parse_context_type = basic_printf_parse_context<Char>;
   template <typename T> using formatter_type = printf_formatter<T>;
 
  private:
@@ -331,7 +336,7 @@ template <typename OutputIt, typename Char> class basic_printf_context {
 
   OutputIt out_;
   basic_format_args<basic_printf_context> args_;
-  basic_format_parse_context<Char> parse_ctx_;
+  parse_context_type parse_ctx_;
 
   static void parse_flags(format_specs& specs, const Char*& it,
                           const Char* end);
@@ -362,7 +367,7 @@ template <typename OutputIt, typename Char> class basic_printf_context {
 
   format_arg arg(int id) const { return args_.get(id); }
 
-  basic_format_parse_context<Char>& parse_context() { return parse_ctx_; }
+  parse_context_type& parse_context() { return parse_ctx_; }
 
   FMT_CONSTEXPR void on_error(const char* message) {
     parse_ctx_.on_error(message);

test/core-test.cc

@@ -210,7 +210,8 @@ TEST(ArgTest, FormatArgs) {
 }
 
 struct custom_context {
-  typedef char char_type;
+  using char_type = char;
+  using parse_context_type = fmt::format_parse_context;
 
   template <typename T> struct formatter_type {
     template <typename ParseContext>

test/format-test.cc

@@ -2259,8 +2259,9 @@ struct test_parse_context {
 };
 
 struct test_context {
-  typedef char char_type;
-  typedef fmt::basic_format_arg<test_context> format_arg;
+  using char_type = char;
+  using format_arg = fmt::basic_format_arg<test_context>;
+  using parse_context_type = fmt::format_parse_context;
 
   template <typename T> struct formatter_type {
     typedef fmt::formatter<T, char_type> type;

test/printf-test.cc

@@ -502,9 +502,7 @@ TEST(PrintfTest, PrintfError) {
 TEST(PrintfTest, WideString) { EXPECT_EQ(L"abc", fmt::sprintf(L"%s", L"abc")); }
 
 TEST(PrintfTest, PrintfCustom) {
-  // The test is disabled for now because it requires decoupling
-  // fallback_formatter::format from format_context.
-  //EXPECT_EQ("abc", test_sprintf("%s", TestString("abc")));
+  EXPECT_EQ("abc", test_sprintf("%s", TestString("abc")));
 }
 
 TEST(PrintfTest, OStream) {