Amalgamate the forward declaration header

.github/CONTRIBUTING.md

@@ -22,17 +22,17 @@ Clearly describe the issue:
 - If you propose a change or addition, try to give an **example** how the improved code could look like or how to use it.
 - If you found a compilation error, please tell us which **compiler** (version and operating system) you used and paste the (relevant part of) the error messages to the ticket.
 
-Please stick to the provided issue templates ([bug report](https://github.com/nlohmann/json/blob/develop/.github/ISSUE_TEMPLATE/Bug_report.md), [feature request](https://github.com/nlohmann/json/blob/develop/.github/ISSUE_TEMPLATE/Feature_request.md), or [question](https://github.com/nlohmann/json/blob/develop/.github/ISSUE_TEMPLATE/question.md)) if possible.
+Please stick to the provided issue template ([bug report](https://github.com/nlohmann/json/blob/develop/.github/ISSUE_TEMPLATE/bug.yml) if possible. For questions, feature or support requests, please [open a discussion](https://github.com/nlohmann/json/discussions/new).
 
 ## Files to change
 
-:exclamation: Before you make any changes, note the single-header file [`single_include/nlohmann/json.hpp`](https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json.hpp) is **generated** from the source files in the [`include/nlohmann` directory](https://github.com/nlohmann/json/tree/develop/include/nlohmann). Please **do not** edit file `single_include/nlohmann/json.hpp` directly, but change the `include/nlohmann` sources and regenerate file `single_include/nlohmann/json.hpp` by executing `make amalgamate`.
+:exclamation: Before you make any changes, note the single-header files [`single_include/nlohmann/json.hpp`](https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json.hpp) and [`single_include/nlohmann/json_fwd.hpp`](https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json_fwd.hpp) are **generated** from the source files in the [`include/nlohmann` directory](https://github.com/nlohmann/json/tree/develop/include/nlohmann). Please **do not** edit the files `single_include/nlohmann/json.hpp` and `single_include/nlohmann/json_fwd.hpp` directly, but change the `include/nlohmann` sources and regenerate the files by executing `make amalgamate`.
 
 To make changes, you need to edit the following files:
 
-1. [`include/nlohmann/*`](https://github.com/nlohmann/json/tree/develop/include/nlohmann) - These files are the sources of the library. Before testing or creating a pull request, execute `make amalgamate` to regenerate `single_include/nlohmann/json.hpp`.
+1. [`include/nlohmann/*`](https://github.com/nlohmann/json/tree/develop/include/nlohmann) - These files are the sources of the library. Before testing or creating a pull request, execute `make amalgamate` to regenerate `single_include/nlohmann/json.hpp` and `single_include/nlohmann/json_fwd.hpp`.
 
-2. [`test/src/unit-*.cpp`](https://github.com/nlohmann/json/tree/develop/test/src) - These files contain the [doctest](https://github.com/onqtam/doctest) unit tests which currently cover [100 %](https://coveralls.io/github/nlohmann/json) of the library's code.
+2. [`tests/src/unit-*.cpp`](https://github.com/nlohmann/json/tree/develop/tests/src) - These files contain the [doctest](https://github.com/onqtam/doctest) unit tests which currently cover [100 %](https://coveralls.io/github/nlohmann/json) of the library's code.
 
    If you add or change a feature, please also add a unit test to this file. The unit tests can be compiled and executed with
 

.github/PULL_REQUEST_TEMPLATE.md

@@ -9,7 +9,7 @@ Read the [Contribution Guidelines](https://github.com/nlohmann/json/blob/develop
 - [ ]  Changes are described in the pull request, or an [existing issue is referenced](https://github.com/nlohmann/json/issues).
 - [ ]  The test suite [compiles and runs](https://github.com/nlohmann/json/blob/develop/README.md#execute-unit-tests) without error.
 - [ ]  [Code coverage](https://coveralls.io/github/nlohmann/json) is 100%. Test cases can be added by editing the [test suite](https://github.com/nlohmann/json/tree/develop/test/src).
-- [ ]  The source code is amalgamated; that is, after making changes to the sources in the `include/nlohmann` directory, run `make amalgamate` to create the single-header file `single_include/nlohmann/json.hpp`. The whole process is described [here](https://github.com/nlohmann/json/blob/develop/.github/CONTRIBUTING.md#files-to-change).
+- [ ]  The source code is amalgamated; that is, after making changes to the sources in the `include/nlohmann` directory, run `make amalgamate` to create the single-header files `single_include/nlohmann/json.hpp` and `single_include/nlohmann/json_fwd.hpp`. The whole process is described [here](https://github.com/nlohmann/json/blob/develop/.github/CONTRIBUTING.md#files-to-change).
 
 ## Please don't
 

Makefile

@@ -18,8 +18,9 @@ SRCS=$(shell find include -type f | sort)
 # the list of sources in the tests folder
 TESTS_SRCS=$(shell find tests -type f \( -name '*.hpp' -o -name '*.cpp' -o -name '*.cu' \) -not -path 'tests/thirdparty/*' -not -path 'tests/abi/include/nlohmann/*' | sort)
 
-# the single header (amalgamated from the source files)
+# the single headers (amalgamated from the source files)
 AMALGAMATED_FILE=single_include/nlohmann/json.hpp
+AMALGAMATED_FWD_FILE=single_include/nlohmann/json_fwd.hpp
 
 
 ##########################################################################
@@ -28,7 +29,7 @@ AMALGAMATED_FILE=single_include/nlohmann/json.hpp
 
 # main target
 all:
-	@echo "amalgamate - amalgamate file single_include/nlohmann/json.hpp from the include/nlohmann sources"
+	@echo "amalgamate - amalgamate files single_include/nlohmann/json{,_fwd}.hpp from the include/nlohmann sources"
 	@echo "ChangeLog.md - generate ChangeLog file"
 	@echo "check-amalgamation - check whether sources have been amalgamated"
 	@echo "clean - remove built files"
@@ -144,9 +145,9 @@ pvs_studio:
 # call the Artistic Style pretty printer on all source files
 pretty:
 	astyle \
-		--style=allman \
-		--indent=spaces=4 \
-		--indent-modifiers \
+	    --style=allman \
+	    --indent=spaces=4 \
+	    --indent-modifiers \
 	    --indent-switches \
 	    --indent-preproc-block \
 	    --indent-preproc-define \
@@ -162,27 +163,34 @@ pretty:
 	    --preserve-date \
 	    --suffix=none \
 	    --formatted \
-	   $(SRCS) $(TESTS_SRCS) $(AMALGAMATED_FILE) docs/examples/*.cpp
+	   $(SRCS) $(TESTS_SRCS) $(AMALGAMATED_FILE) $(AMALGAMATED_FWD_FILE) docs/examples/*.cpp
 
 # call the Clang-Format on all source files
 pretty_format:
 	for FILE in $(SRCS) $(TESTS_SRCS) $(AMALGAMATED_FILE) docs/examples/*.cpp; do echo $$FILE; clang-format -i $$FILE; done
 
-# create single header file
-amalgamate: $(AMALGAMATED_FILE)
+# create single header files and pretty print
+amalgamate: $(AMALGAMATED_FILE) $(AMALGAMATED_FWD_FILE)
+	$(MAKE) pretty
 
-# call the amalgamation tool and pretty print
+# call the amalgamation tool for json.hpp
 $(AMALGAMATED_FILE): $(SRCS)
-	tools/amalgamate/amalgamate.py -c tools/amalgamate/config.json -s . --verbose=yes
-	$(MAKE) pretty
+	tools/amalgamate/amalgamate.py -c tools/amalgamate/config_json.json -s . --verbose=yes
+
+# call the amalgamation tool for json_fwd.hpp
+$(AMALGAMATED_FWD_FILE): $(SRCS)
+	tools/amalgamate/amalgamate.py -c tools/amalgamate/config_json_fwd.json -s . --verbose=yes
 
 # check if file single_include/nlohmann/json.hpp has been amalgamated from the nlohmann sources
 # Note: this target is called by Travis
 check-amalgamation:
 	@mv $(AMALGAMATED_FILE) $(AMALGAMATED_FILE)~
+	@mv $(AMALGAMATED_FWD_FILE) $(AMALGAMATED_FWD_FILE)~
 	@$(MAKE) amalgamate
 	@diff $(AMALGAMATED_FILE) $(AMALGAMATED_FILE)~ || (echo "===================================================================\n  Amalgamation required! Please read the contribution guidelines\n  in file .github/CONTRIBUTING.md.\n===================================================================" ; mv $(AMALGAMATED_FILE)~ $(AMALGAMATED_FILE) ; false)
+	@diff $(AMALGAMATED_FWD_FILE) $(AMALGAMATED_FWD_FILE)~ || (echo "===================================================================\n  Amalgamation required! Please read the contribution guidelines\n  in file .github/CONTRIBUTING.md.\n===================================================================" ; mv $(AMALGAMATED_FWD_FILE)~ $(AMALGAMATED_FWD_FILE) ; false)
 	@mv $(AMALGAMATED_FILE)~ $(AMALGAMATED_FILE)
+	@mv $(AMALGAMATED_FWD_FILE)~ $(AMALGAMATED_FWD_FILE)
 
 
 ##########################################################################

cmake/ci.cmake

@@ -589,15 +589,22 @@ file(GLOB_RECURSE INDENT_FILES
     ${PROJECT_SOURCE_DIR}/docs/examples/*.cpp
 )
 
+set(include_dir ${PROJECT_SOURCE_DIR}/single_include/nlohmann)
+set(tool_dir ${PROJECT_SOURCE_DIR}/tools/amalgamate)
 add_custom_target(ci_test_amalgamation
-    COMMAND rm -fr ${PROJECT_SOURCE_DIR}/single_include/nlohmann/json.hpp~
-    COMMAND cp ${PROJECT_SOURCE_DIR}/single_include/nlohmann/json.hpp ${PROJECT_SOURCE_DIR}/single_include/nlohmann/json.hpp~
-    COMMAND ${Python3_EXECUTABLE} ${PROJECT_SOURCE_DIR}/tools/amalgamate/amalgamate.py -c ${PROJECT_SOURCE_DIR}/tools/amalgamate/config.json -s .
-    COMMAND ${ASTYLE_TOOL} ${ASTYLE_FLAGS} --suffix=none --quiet ${PROJECT_SOURCE_DIR}/single_include/nlohmann/json.hpp
-    COMMAND diff ${PROJECT_SOURCE_DIR}/single_include/nlohmann/json.hpp~ ${PROJECT_SOURCE_DIR}/single_include/nlohmann/json.hpp
+    COMMAND rm -fr ${include_dir}/json.hpp~ ${include_dir}/json_fwd.hpp~
+    COMMAND cp ${include_dir}/json.hpp ${include_dir}/json.hpp~
+    COMMAND cp ${include_dir}/json_fwd.hpp ${include_dir}/json_fwd.hpp~
+
+    COMMAND ${Python3_EXECUTABLE} ${tool_dir}/amalgamate.py -c ${tool_dir}/config_json.json -s .
+    COMMAND ${Python3_EXECUTABLE} ${tool_dir}/amalgamate.py -c ${tool_dir}/config_json_fwd.json -s .
+    COMMAND ${ASTYLE_TOOL} ${ASTYLE_FLAGS} --suffix=none --quiet ${include_dir}/json.hpp ${include_dir}/json_fwd.hpp
+
+    COMMAND diff ${include_dir}/json.hpp~ ${include_dir}/json.hpp
+    COMMAND diff ${include_dir}/json_fwd.hpp~ ${include_dir}/json_fwd.hpp
 
     COMMAND ${ASTYLE_TOOL} ${ASTYLE_FLAGS} ${INDENT_FILES}
-    COMMAND cd ${PROJECT_SOURCE_DIR} && for FILE in `find . -name '*.orig'`\; do false \; done
+    COMMAND for FILE in `find . -name '*.orig'`\; do false \; done
 
     WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
     COMMENT "Check amalgamation and indentation"

docs/mkdocs/docs/integration/index.md

@@ -13,6 +13,6 @@ using json = nlohmann::json;
 to the files you want to process JSON and set the necessary switches to enable C++11 (e.g., `-std=c++11` for GCC and
 Clang).
 
-You can further use file [`include/nlohmann/json_fwd.hpp`](https://github.com/nlohmann/json/blob/develop/include/nlohmann/json_fwd.hpp)
-for forward-declarations. The installation of `json_fwd.hpp` (as part of CMake's install step), can be achieved by
-setting `-DJSON_MultipleHeaders=ON`.
+You can further use file
+[`single_include/nlohmann/json_fwd.hpp`](https://github.com/nlohmann/json/blob/develop/single_include/nlohmann/json_fwd.hpp)
+for forward declarations.

single_include/nlohmann/json_fwd.hpp

@@ -0,0 +1,154 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++
+// |  |  |__   |  |  | | | |  version 3.11.1
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2022 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#ifndef INCLUDE_NLOHMANN_JSON_FWD_HPP_
+#define INCLUDE_NLOHMANN_JSON_FWD_HPP_
+
+#include <cstdint> // int64_t, uint64_t
+#include <map> // map
+#include <memory> // allocator
+#include <string> // string
+#include <vector> // vector
+
+// #include <nlohmann/detail/abi_macros.hpp>
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++
+// |  |  |__   |  |  | | | |  version 3.11.1
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2022 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+
+
+// This file contains all macro definitions affecting or depending on the ABI
+
+#ifndef JSON_SKIP_LIBRARY_VERSION_CHECK
+    #if defined(NLOHMANN_JSON_VERSION_MAJOR) && defined(NLOHMANN_JSON_VERSION_MINOR) && defined(NLOHMANN_JSON_VERSION_PATCH)
+        #if NLOHMANN_JSON_VERSION_MAJOR != 3 || NLOHMANN_JSON_VERSION_MINOR != 11 || NLOHMANN_JSON_VERSION_PATCH != 1
+            #warning "Already included a different version of the library!"
+        #endif
+    #endif
+#endif
+
+#define NLOHMANN_JSON_VERSION_MAJOR 3   // NOLINT(modernize-macro-to-enum)
+#define NLOHMANN_JSON_VERSION_MINOR 11  // NOLINT(modernize-macro-to-enum)
+#define NLOHMANN_JSON_VERSION_PATCH 1   // NOLINT(modernize-macro-to-enum)
+
+#ifndef JSON_DIAGNOSTICS
+    #define JSON_DIAGNOSTICS 0
+#endif
+
+#ifndef JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON
+    #define JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON 0
+#endif
+
+#if JSON_DIAGNOSTICS
+    #define NLOHMANN_JSON_ABI_TAG_DIAGNOSTICS _diag
+#else
+    #define NLOHMANN_JSON_ABI_TAG_DIAGNOSTICS
+#endif
+
+#if JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON
+    #define NLOHMANN_JSON_ABI_TAG_LEGACY_DISCARDED_VALUE_COMPARISON _ldvcmp
+#else
+    #define NLOHMANN_JSON_ABI_TAG_LEGACY_DISCARDED_VALUE_COMPARISON
+#endif
+
+#define NLOHMANN_JSON_ABI_PREFIX_EX(major, minor, patch) \
+    json_v ## major ## _ ## minor ## _ ## patch
+#define NLOHMANN_JSON_ABI_PREFIX(major, minor, patch) \
+    NLOHMANN_JSON_ABI_PREFIX_EX(major, minor, patch)
+
+#define NLOHMANN_JSON_ABI_CONCAT_EX(a, b, c) a ## b ## c
+#define NLOHMANN_JSON_ABI_CONCAT(a, b, c) \
+    NLOHMANN_JSON_ABI_CONCAT_EX(a, b, c)
+
+#define NLOHMANN_JSON_ABI_STRING                                    \
+    NLOHMANN_JSON_ABI_CONCAT(                                       \
+            NLOHMANN_JSON_ABI_PREFIX(                               \
+                    NLOHMANN_JSON_VERSION_MAJOR,                    \
+                    NLOHMANN_JSON_VERSION_MINOR,                    \
+                    NLOHMANN_JSON_VERSION_PATCH),                   \
+            NLOHMANN_JSON_ABI_TAG_DIAGNOSTICS,                      \
+            NLOHMANN_JSON_ABI_TAG_LEGACY_DISCARDED_VALUE_COMPARISON)
+
+#ifndef NLOHMANN_JSON_NAMESPACE
+    #define NLOHMANN_JSON_NAMESPACE nlohmann::NLOHMANN_JSON_ABI_STRING
+#endif
+
+#ifndef NLOHMANN_JSON_NAMESPACE_BEGIN
+#define NLOHMANN_JSON_NAMESPACE_BEGIN         \
+    namespace nlohmann                        \
+    {                                         \
+    inline namespace NLOHMANN_JSON_ABI_STRING \
+    {
+#endif
+
+#ifndef NLOHMANN_JSON_NAMESPACE_END
+#define NLOHMANN_JSON_NAMESPACE_END \
+    }  /* namespace (abi_string) */ \
+    }  /* namespace nlohmann */
+#endif
+
+
+/*!
+@brief namespace for Niels Lohmann
+@see https://github.com/nlohmann
+@since version 1.0.0
+*/
+NLOHMANN_JSON_NAMESPACE_BEGIN
+
+/*!
+@brief default JSONSerializer template argument
+
+This serializer ignores the template arguments and uses ADL
+([argument-dependent lookup](https://en.cppreference.com/w/cpp/language/adl))
+for serialization.
+*/
+template<typename T = void, typename SFINAE = void>
+struct adl_serializer;
+
+/// a class to store JSON values
+/// @sa https://json.nlohmann.me/api/basic_json/
+template<template<typename U, typename V, typename... Args> class ObjectType =
+         std::map,
+         template<typename U, typename... Args> class ArrayType = std::vector,
+         class StringType = std::string, class BooleanType = bool,
+         class NumberIntegerType = std::int64_t,
+         class NumberUnsignedType = std::uint64_t,
+         class NumberFloatType = double,
+         template<typename U> class AllocatorType = std::allocator,
+         template<typename T, typename SFINAE = void> class JSONSerializer =
+         adl_serializer,
+         class BinaryType = std::vector<std::uint8_t>>
+class basic_json;
+
+/// @brief JSON Pointer defines a string syntax for identifying a specific value within a JSON document
+/// @sa https://json.nlohmann.me/api/json_pointer/
+template<typename RefStringType>
+class json_pointer;
+
+/*!
+@brief default specialization
+@sa https://json.nlohmann.me/api/json/
+*/
+using json = basic_json<>;
+
+/// @brief a minimal map-like container that preserves insertion order
+/// @sa https://json.nlohmann.me/api/ordered_map/
+template<class Key, class T, class IgnoredLess, class Allocator>
+struct ordered_map;
+
+/// @brief specialization that maintains the insertion order of object keys
+/// @sa https://json.nlohmann.me/api/ordered_json/
+using ordered_json = basic_json<nlohmann::ordered_map>;
+
+NLOHMANN_JSON_NAMESPACE_END
+
+#endif  // INCLUDE_NLOHMANN_JSON_FWD_HPP_

tools/amalgamate/config_json_fwd.json

@@ -0,0 +1,8 @@
+{
+	"project": "JSON for Modern C++",
+	"target": "single_include/nlohmann/json_fwd.hpp",
+	"sources": [
+		"include/nlohmann/json_fwd.hpp"
+	],
+	"include_paths": ["include"]
+}