♻️ reorganize PR

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

tests/CMakeLists.txt

@@ -195,3 +195,4 @@ add_subdirectory(cmake_add_subdirectory)
 add_subdirectory(cmake_fetch_content)
 add_subdirectory(cmake_fetch_content2)
 add_subdirectory(cmake_target_include_directories)
+add_subdirectory(fmt_formatter)

tests/fmt_formatter/CMakeLists.txt

@@ -0,0 +1,20 @@
+if (${CMAKE_VERSION} VERSION_GREATER "3.14.0")
+  add_test(NAME fmt_formatter_configure
+    COMMAND ${CMAKE_COMMAND}
+    -G "${CMAKE_GENERATOR}"
+    -DCMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER}
+    -DCMAKE_CXX_FLAGS=${CMAKE_CXX_FLAGS}
+    ${CMAKE_CURRENT_SOURCE_DIR}/project
+  )
+  add_test(NAME fmt_formatter_build
+    COMMAND ${CMAKE_COMMAND} --build .
+  )
+  set_tests_properties(fmt_formatter_configure PROPERTIES
+    FIXTURES_SETUP fmt_formatter
+    LABELS "git_required;not_reproducible"
+  )
+  set_tests_properties(fmt_formatter_build PROPERTIES
+    FIXTURES_REQUIRED fmt_formatter
+    LABELS "git_required;not_reproducible"
+  )
+endif()

tests/fmt_formatter/project/CMakeLists.txt

@@ -0,0 +1,36 @@
+cmake_minimum_required(VERSION 3.14)
+
+project(FmtFormatterTest CXX)
+
+include(FetchContent)
+
+get_filename_component(GIT_REPOSITORY_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/../../.. ABSOLUTE)
+FetchContent_Declare(json GIT_REPOSITORY ${GIT_REPOSITORY_DIRECTORY} GIT_TAG HEAD)
+
+set(FMT_TEST OFF CACHE BOOL "" FORCE)
+set(FMT_DOC OFF CACHE BOOL "" FORCE)
+set(FMT_INSTALL OFF CACHE BOOL "" FORCE)
+FetchContent_Declare(fmt
+  GIT_REPOSITORY https://github.com/fmtlib/fmt.git
+  GIT_TAG 12.2.0
+  GIT_SHALLOW TRUE
+)
+
+FetchContent_MakeAvailable(json fmt)
+
+if(MSVC)
+  add_compile_options(/EHsc)
+endif()
+
+add_executable(fmt_formatter_test main.cpp)
+target_link_libraries(fmt_formatter_test PRIVATE nlohmann_json::nlohmann_json fmt::fmt)
+target_compile_features(fmt_formatter_test PRIVATE cxx_std_17)
+
+# Fail the build itself (and therefore the ctest "build" step that drives it) if the
+# recipe's runtime assertions don't hold -- there is no separate "run" step, since the
+# executable's location varies by platform/generator, but CMake resolves a target name
+# passed to a custom command's COMMAND for us.
+add_custom_command(TARGET fmt_formatter_test POST_BUILD
+  COMMAND fmt_formatter_test
+  COMMENT "Running fmt::formatter<nlohmann::json> recipe test"
+)

tests/fmt_formatter/project/main.cpp

@@ -0,0 +1,98 @@
+#include <cassert>
+#include <fmt/format.h>
+#include <nlohmann/json.hpp>
+
+// A fmt::formatter<nlohmann::json> specialization mirroring std::formatter<basic_json>
+// (see docs/mkdocs/docs/api/basic_json/std_formatter.md), for use with fmt versions that
+// no longer pick up format_as() (fmt >= 11.1.0), or to get the same "{:#}"/width/
+// fill-and-align spec support with any fmt version.
+// --8<-- [start:formatter_recipe]
+template <>
+struct fmt::formatter<nlohmann::json>
+{
+    // -1 means compact output (dump()); any value >= 0 means pretty-printed
+    // output with that many spaces (or indent_char) per level.
+    int indent = -1;
+    char indent_char = ' ';
+
+    constexpr auto parse(format_parse_context& ctx) -> format_parse_context::iterator
+    {
+        auto it = ctx.begin();
+        const auto end = ctx.end();
+        constexpr auto is_align = [](char c)
+        {
+            return c == '<' || c == '>' || c == '^';
+        };
+
+        // [[fill] align] - repurposed here to pick a custom indent character
+        if (it != end && it + 1 != end && is_align(it[1]))
+        {
+            indent_char = *it;
+            it += 2;
+        }
+        else if (it != end && is_align(*it))
+        {
+            ++it;
+        }
+
+        // ['#'] - "alternate form", used here to request pretty-printing
+        bool pretty = false;
+        if (it != end && *it == '#')
+        {
+            pretty = true;
+            ++it;
+        }
+
+        // [width] - repurposed here to pick the indent size; a width without '#'
+        // implies pretty-printing since an indent otherwise has no meaning
+        if (it != end && *it >= '1' && *it <= '9')
+        {
+            indent = 0;
+            while (it != end && *it >= '0' && *it <= '9')
+            {
+                indent = (indent * 10) + (*it - '0');
+                ++it;
+            }
+        }
+        else if (pretty)
+        {
+            indent = 4;
+        }
+
+        if (it != end && *it != '}')
+        {
+            throw fmt::format_error("invalid format args for nlohmann::json");
+        }
+
+        return it;
+    }
+
+    auto format(const nlohmann::json& j, format_context& ctx) const
+    {
+        const auto dumped = j.dump(indent, indent_char);
+        return fmt::format_to(ctx.out(), "{}", dumped);
+    }
+};
+// --8<-- [end:formatter_recipe]
+
+int main()
+{
+    const nlohmann::json j = {{"foo", 1}, {"bar", {1, 2, 3}}};
+
+    assert(fmt::format("{}", j) == j.dump());
+    assert(fmt::format("{:#}", j) == j.dump(4));
+    assert(fmt::format("{:2}", j) == j.dump(2));
+    assert(fmt::format("{:#2}", j) == j.dump(2));
+    assert(fmt::format("{:.>#}", j) == j.dump(4, '.'));
+
+    bool threw = false;
+    try
+    {
+        (void)fmt::vformat("{:x}", fmt::make_format_args(j));
+    }
+    catch (const fmt::format_error&)
+    {
+        threw = true;
+    }
+    assert(threw);
+}

tests/src/unit-std-format.cpp

@@ -46,7 +46,27 @@ TEST_CASE("std::formatter<nlohmann::json>")
         CHECK(std::format("{:#}", json::array()) == json::array().dump(4));
     }
 
-    SECTION("format args other than an empty spec or '#' are rejected")
+    SECTION("a width sets the indent, like dump(width), with or without '#'")
+    {
+        const json j = {{"foo", 1}, {"bar", {1, 2, 3}}};
+        CHECK(std::format("{:2}", j) == j.dump(2));
+        CHECK(std::format("{:#2}", j) == j.dump(2));
+        CHECK(std::format("{:8}", j) == j.dump(8));
+    }
+
+    SECTION("fill-and-align sets the indent character, like dump(indent, indent_char)")
+    {
+        const json j = {{"foo", 1}, {"bar", {1, 2, 3}}};
+        CHECK(std::format("{:.>#}", j) == j.dump(4, '.'));
+        CHECK(std::format("{:.>#3}", j) == j.dump(3, '.'));
+        CHECK(std::format("{:.>3}", j) == j.dump(3, '.'));
+        // the alignment direction itself ('<', '>', '^') has no separate meaning for
+        // JSON values -- only the fill character before it is used as the indent character
+        CHECK(std::format("{:.<3}", j) == j.dump(3, '.'));
+        CHECK(std::format("{:.^3}", j) == j.dump(3, '.'));
+    }
+
+    SECTION("format args with no meaning for JSON values are rejected")
     {
         // std::vformat parses the format string at runtime (unlike std::format, whose
         // format_string type is checked at compile time), so it lets us verify that an
@@ -54,7 +74,14 @@ TEST_CASE("std::formatter<nlohmann::json>")
         // format string.
         const json j = 42;
         CHECK_THROWS_AS(std::vformat("{:x}", std::make_format_args(j)), std::format_error);
-        CHECK_THROWS_AS(std::vformat("{:10}", std::make_format_args(j)), std::format_error);
+        CHECK_THROWS_AS(std::vformat("{:+}", std::make_format_args(j)), std::format_error);   // sign
+        CHECK_THROWS_AS(std::vformat("{:-}", std::make_format_args(j)), std::format_error);   // sign
+        CHECK_THROWS_AS(std::vformat("{: }", std::make_format_args(j)), std::format_error);   // sign
+        CHECK_THROWS_AS(std::vformat("{:04}", std::make_format_args(j)), std::format_error);  // '0' flag
+        CHECK_THROWS_AS(std::vformat("{:.2}", std::make_format_args(j)), std::format_error);  // precision
+        CHECK_THROWS_AS(std::vformat("{:L}", std::make_format_args(j)), std::format_error);   // locale
+        const int dynamic_width = 4;
+        CHECK_THROWS_AS(std::vformat("{:{}}", std::make_format_args(j, dynamic_width)), std::format_error); // dynamic width
     }
 
     SECTION("std::format_to writes through an arbitrary output iterator")