From 06c005b7b0bba63d4d7a36cd28e144cdf17f6403 Mon Sep 17 00:00:00 2001
From: Victor Zverovich <victor.zverovich@gmail.com>
Date: Sun, 27 Jan 2019 09:05:50 -0800
Subject: [PATCH] Clarify that compile-time checks don't support named
 arguments

---
 doc/api.rst          |  3 +++
 include/fmt/format.h | 14 +++++++++++++-
 test/format-test.cc  |  3 ++-
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/doc/api.rst b/doc/api.rst
index 33a4f6d2..bf8dbbe6 100644
--- a/doc/api.rst
+++ b/doc/api.rst
@@ -56,6 +56,8 @@ Named arguments
 
 .. doxygenfunction:: fmt::arg(string_view, const T&)
 
+Named arguments are not supported in compile-time checks at the moment.
+
 Argument lists
 --------------
 
@@ -92,6 +94,7 @@ string checks, output iterator and user-defined type support.
 Compile-time format string checks
 ---------------------------------
 
+.. doxygendefine:: FMT_STRING
 .. doxygendefine:: fmt
 
 Formatting user-defined types
diff --git a/include/fmt/format.h b/include/fmt/format.h
index 1c05b0ea..4be16c05 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -2117,7 +2117,9 @@ class format_string_checker {
     context_.check_arg_id(id);
     check_arg_id();
   }
-  FMT_CONSTEXPR void on_arg_id(basic_string_view<Char>) {}
+  FMT_CONSTEXPR void on_arg_id(basic_string_view<Char>) {
+    on_error("compile-time checks don't support named arguments");
+  }
 
   FMT_CONSTEXPR void on_replacement_field(const Char*) {}
 
@@ -3495,6 +3497,16 @@ inline internal::udl_arg<wchar_t> operator"" _a(const wchar_t* s, std::size_t) {
 #endif  // FMT_USE_USER_DEFINED_LITERALS
 FMT_END_NAMESPACE
 
+/**
+  \rst
+  Constructs a compile-time format string.
+
+  **Example**::
+
+    // A compile-time error because 'd' is an invalid specifier for strings.
+    std::string s = format(FMT_STRING("{:d}"), "foo");
+  \endrst
+ */
 #define FMT_STRING(s)                                                     \
   [] {                                                                    \
     struct str : fmt::compile_string {                                    \
diff --git a/test/format-test.cc b/test/format-test.cc
index 14022468..84142ffc 100644
--- a/test/format-test.cc
+++ b/test/format-test.cc
@@ -2357,7 +2357,8 @@ TEST(FormatTest, FormatStringErrors) {
   EXPECT_ERROR("{:d}", "invalid type specifier", std::string);
   EXPECT_ERROR("{:s}", "invalid type specifier", void*);
 #  endif
-  EXPECT_ERROR("{foo", "missing '}' in format string", int);
+  EXPECT_ERROR("{foo",
+               "compile-time checks don't support named arguments", int);
   EXPECT_ERROR_NOARGS("{10000000000}", "number is too big");
   EXPECT_ERROR_NOARGS("{0x}", "invalid format string");
   EXPECT_ERROR_NOARGS("{-}", "invalid format string");