Add support for s format specifier to bool (#2094)

Author: powercoderlol

include/fmt/format.h

@@ -1423,6 +1423,14 @@ FMT_CONSTEXPR void handle_int_type_spec(char spec, Handler&& handler) {
   }
 }
 
+template <typename Char, typename Handler>
+FMT_CONSTEXPR void handle_bool_type_spec(const basic_format_specs<Char>* specs,
+                                         Handler&& handler) {
+  if (!specs) return handler.on_str();
+  if (specs->type && specs->type != 's') return handler.on_int();
+  handler.on_str();
+}
+
 template <typename ErrorHandler = error_handler, typename Char>
 FMT_CONSTEXPR float_specs parse_float_type_spec(
     const basic_format_specs<Char>& specs, ErrorHandler&& eh = {}) {
@@ -1542,6 +1550,21 @@ class cstring_type_checker : public ErrorHandler {
   FMT_CONSTEXPR void on_pointer() {}
 };
 
+template <typename ErrorHandler>
+class bool_type_checker : private ErrorHandler {
+ private:
+  char type_;
+
+ public:
+  FMT_CONSTEXPR explicit bool_type_checker(char type, ErrorHandler eh)
+      : ErrorHandler(eh), type_(type) {}
+
+  FMT_CONSTEXPR void on_int() {
+    handle_int_type_spec(type_, int_type_checker<ErrorHandler>(*this));
+  }
+  FMT_CONSTEXPR void on_str() {}
+};
+
 template <typename OutputIt, typename Char>
 FMT_NOINLINE FMT_CONSTEXPR OutputIt fill(OutputIt it, size_t n,
                                          const fill_t<Char>& fill) {
@@ -2344,7 +2367,8 @@ class arg_formatter_base {
   }
 
   FMT_CONSTEXPR iterator operator()(bool value) {
-    if (specs_ && specs_->type) return (*this)(value ? 1 : 0);
+    if (specs_ && specs_->type && specs_->type != 's')
+      return (*this)(value ? 1 : 0);
     write(value != 0);
     return out_;
   }
@@ -3515,10 +3539,13 @@ struct formatter<T, Char,
     case detail::type::ulong_long_type:
     case detail::type::int128_type:
     case detail::type::uint128_type:
-    case detail::type::bool_type:
       handle_int_type_spec(specs_.type,
                            detail::int_type_checker<decltype(eh)>(eh));
       break;
+    case detail::type::bool_type:
+      handle_bool_type_spec(
+          &specs_, detail::bool_type_checker<decltype(eh)>(specs_.type, eh));
+      break;
     case detail::type::char_type:
       handle_char_specs(
           &specs_, detail::char_specs_checker<decltype(eh)>(specs_.type, eh));

test/format-test.cc

@@ -1129,6 +1129,9 @@ TEST(BoolTest, FormatBool) {
   EXPECT_EQ("1", format("{:d}", true));
   EXPECT_EQ("true ", format("{:5}", true));
   EXPECT_EQ(L"true", format(L"{}", true));
+  EXPECT_EQ("true", format("{:s}", true));
+  EXPECT_EQ("false", format("{:s}", false));
+  EXPECT_EQ("false ", format("{:6s}", false));
 }
 
 TEST(FormatterTest, FormatShort) {
@@ -2435,7 +2438,6 @@ TEST(FormatTest, FormatStringErrors) {
   EXPECT_ERROR("{:.{}}", "argument not found", double);
   EXPECT_ERROR("{:.2}", "precision not allowed for this argument type", int);
   EXPECT_ERROR("{:s}", "invalid type specifier", int);
-  EXPECT_ERROR("{:s}", "invalid type specifier", bool);
   EXPECT_ERROR("{:s}", "invalid type specifier", char);
   EXPECT_ERROR("{:+}", "invalid format specifier for char", char);
   EXPECT_ERROR("{:s}", "invalid type specifier", double);