AK: Add support for "debug only" formatters

These are formatters that can only be used with debug print
functions, such as dbgln(). Currently this is limited to
Formatter<ErrorOr<T>>. With this you can still debug log ErrorOr
values (good for debugging), but trying to use them in any
String::formatted() call will fail (which prevents .to_string()
errors with the new failable strings being ignored).

You make a formatter debug only by adding a constexpr method like:
static constexpr bool is_debug_only() { return true; }

1 files changed, 2 insertions, 2 deletions

diff --git a/AK/StringBuilder.h b/AK/StringBuilder.h
index 5e28ef0300..98299ea86b 100644
--- a/AK/StringBuilder.h
+++ b/AK/StringBuilder.h
@@ -33,7 +33,7 @@ public:
     template<typename... Parameters>
     ErrorOr<void> try_appendff(CheckedFormatString<Parameters...>&& fmtstr, Parameters const&... parameters)
     {
-        VariadicFormatParams variadic_format_params { parameters... };
+        VariadicFormatParams<AllowDebugOnlyFormatters::No, Parameters...> variadic_format_params { parameters... };
         return vformat(*this, fmtstr.view(), variadic_format_params);
     }
     ErrorOr<void> try_append(char const*, size_t);
@@ -57,7 +57,7 @@ public:
     template<typename... Parameters>
     void appendff(CheckedFormatString<Parameters...>&& fmtstr, Parameters const&... parameters)
     {
-        VariadicFormatParams variadic_format_params { parameters... };
+        VariadicFormatParams<AllowDebugOnlyFormatters::No, Parameters...> variadic_format_params { parameters... };
         MUST(vformat(*this, fmtstr.view(), variadic_format_params));
     }