Merge branch 'develop' of https://github.com/nlohmann/json into featu…

…re/optional

.cirrus.yml

@@ -0,0 +1,17 @@
+arm_container:
+  image: gcc:latest
+
+check_task:
+  check_script:
+  - wget https://github.com/Kitware/CMake/releases/download/v3.20.2/cmake-3.20.2.tar.gz
+  - tar xfz cmake-3.20.2.tar.gz
+  - cd cmake-3.20.2
+  - ./configure
+  - make cmake ctest -j4
+  - cd ..
+  - mkdir build
+  - cd build
+  - ../cmake-3.20.2/bin/cmake .. -DJSON_FastTests=ON
+  - make -j4
+  - cd tests
+  - ../../cmake-3.20.2/bin/ctest -j4

.clang-tidy

@@ -1,23 +1,59 @@
 Checks: '*,
+         -altera-id-dependent-backward-branch,
+         -altera-struct-pack-align,
+         -altera-unroll-loops,
+         -android-cloexec-fopen,
+         -bugprone-easily-swappable-parameters,
+         -cert-err58-cpp,
+         -concurrency-mt-unsafe,
+         -cppcoreguidelines-avoid-const-or-ref-data-members,
+         -cppcoreguidelines-avoid-do-while,
          -cppcoreguidelines-avoid-goto,
          -cppcoreguidelines-avoid-magic-numbers,
+         -cppcoreguidelines-avoid-non-const-global-variables,
          -cppcoreguidelines-macro-usage,
+         -cppcoreguidelines-pro-bounds-array-to-pointer-decay,
+         -cppcoreguidelines-pro-bounds-constant-array-index,
+         -cppcoreguidelines-pro-bounds-pointer-arithmetic,
+         -cppcoreguidelines-pro-type-reinterpret-cast,
+         -cppcoreguidelines-pro-type-union-access,
+         -cppcoreguidelines-virtual-class-destructor,
          -fuchsia-default-arguments-calls,
          -fuchsia-default-arguments-declarations,
          -fuchsia-overloaded-operator,
          -google-explicit-constructor,
+         -google-readability-function-size,
+         -google-runtime-int,
          -google-runtime-references,
          -hicpp-avoid-goto,
          -hicpp-explicit-conversions,
+         -hicpp-function-size,
          -hicpp-no-array-decay,
+         -hicpp-no-assembler,
+         -hicpp-signed-bitwise,
          -hicpp-uppercase-literal-suffix,
          -llvm-header-guard,
          -llvm-include-order,
+         -llvmlibc-*,
+         -misc-confusable-identifiers,
+         -misc-no-recursion,
          -misc-non-private-member-variables-in-classes,
+         -modernize-concat-nested-namespaces,
+         -modernize-use-nodiscard,
          -modernize-use-trailing-return-type,
+         -readability-function-cognitive-complexity,
+         -readability-function-size,
+         -readability-identifier-length,
          -readability-magic-numbers,
+         -readability-redundant-access-specifiers,
+         -readability-simplify-boolean-expr,
          -readability-uppercase-literal-suffix'
 
 CheckOptions:
   - key: hicpp-special-member-functions.AllowSoleDefaultDtor
     value: 1
+
+WarningsAsErrors: '*'
+
+#HeaderFilterRegex: '.*nlohmann.*'
+HeaderFilterRegex: '.*hpp$'

.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
 
@@ -55,10 +55,10 @@ To make changes, you need to edit the following files:
 ## Please don't
 
 - The C++11 support varies between different **compilers** and versions. Please note the [list of supported compilers](https://github.com/nlohmann/json/blob/master/README.md#supported-compilers). Some compilers like GCC 4.7 (and earlier), Clang 3.3 (and earlier), or Microsoft Visual Studio 13.0 and earlier are known not to work due to missing or incomplete C++11 support. Please refrain from proposing changes that work around these compiler's limitations with `#ifdef`s or other means.
-- Specifically, I am aware of compilation problems with **Microsoft Visual Studio** (there even is an [issue label](https://github.com/nlohmann/json/issues?utf8=✓&q=label%3A%22visual+studio%22+) for these kind of bugs). I understand that even in 2016, complete C++11 support isn't there yet. But please also understand that I do not want to drop features or uglify the code just to make Microsoft's sub-standard compiler happy. The past has shown that there are ways to express the functionality such that the code compiles with the most recent MSVC - unfortunately, this is not the main objective of the project.
+- Specifically, I am aware of compilation problems with **Microsoft Visual Studio** (there even is an [issue label](https://github.com/nlohmann/json/issues?utf8=✓&q=label%3A%22visual+studio%22+) for this kind of bug). I understand that even in 2016, complete C++11 support isn't there yet. But please also understand that I do not want to drop features or uglify the code just to make Microsoft's sub-standard compiler happy. The past has shown that there are ways to express the functionality such that the code compiles with the most recent MSVC - unfortunately, this is not the main objective of the project.
 - Please refrain from proposing changes that would **break [JSON](https://json.org) conformance**. If you propose a conformant extension of JSON to be supported by the library, please motivate this extension.
   - We shall not extend the library to **support comments**. There is quite some [controversy](https://www.reddit.com/r/programming/comments/4v6chu/why_json_doesnt_support_comments_douglas_crockford/) around this topic, and there were quite some [issues](https://github.com/nlohmann/json/issues/376) on this. We believe that JSON is fine without comments.
-  - We do not preserve the **insertion order of object elements**. The [JSON standard](https://tools.ietf.org/html/rfc7159.html) defines objects as "an unordered collection of zero or more name/value pairs". To this end, this library does not preserve insertion order of name/value pairs. (In fact, keys will be traversed in alphabetical order as `std::map` with `std::less` is used by default.) Note this behavior conforms to the standard, and we shall not change it to any other order. If you do want to preserve the insertion order, you can specialize the object type with containers like [`tsl::ordered_map`](https://github.com/Tessil/ordered-map) or [`nlohmann::fifo_map`](https://github.com/nlohmann/fifo_map).
+  - We do not preserve the **insertion order of object elements**. The [JSON standard](https://tools.ietf.org/html/rfc8259.html) defines objects as "an unordered collection of zero or more name/value pairs". To this end, this library does not preserve insertion order of name/value pairs. (In fact, keys will be traversed in alphabetical order as `std::map` with `std::less` is used by default.) Note this behavior conforms to the standard, and we shall not change it to any other order. If you do want to preserve the insertion order, you can specialize the object type with containers like [`tsl::ordered_map`](https://github.com/Tessil/ordered-map) or [`nlohmann::fifo_map`](https://github.com/nlohmann/fifo_map).
 
 - Please do not open pull requests that address **multiple issues**.
 

.github/ISSUE_TEMPLATE/bug.yaml

@@ -0,0 +1,93 @@
+name: Bug Report
+description: Create a bug report
+labels:
+  - 'kind: bug'
+body:
+  - type: markdown
+    attributes:
+      value: >
+        Thanks for taking the time to fill out this bug report!
+        
+        Make sure you give it a short and specific **title** so that the report
+        is searchable and uniquely identifiable.
+        
+        Note that this form is for bug reports only. Please
+        [open a discussion](https://github.com/nlohmann/json/discussions/new)
+        for questions, feature requests, or support requests
+  - type: textarea
+    id: summary
+    attributes:
+      label: Description
+      description: >
+        Please provide an abstract description of the issue to the developers,
+        and why you consider it to be a bug. Please include any specific links
+        to the documentation, JSON specification, or code.
+    validations:
+      required: true
+  - type: textarea
+    id: reproduce
+    attributes:
+      label: Reproduction steps
+      description: >
+        How do you trigger the bug? Please walk us through step by step. Be as
+        specific as possible.
+    validations:
+      required: true
+  - type: textarea
+    id: results
+    attributes:
+      label: Expected vs. actual results
+      description: >
+        Please describe what you expected to happen after the steps above and
+        what actually happened.
+    validations:
+      required: true
+  - type: textarea
+    id: code
+    attributes:
+      label: Minimal code example
+      description: >
+        If possible, provide a small and self-contained example that triggers
+        the bug. Please understand that we cannot analyze and debug large code
+        bases. Please do not paste screenshots here.
+      render: Shell
+  - type: textarea
+    id: output
+    attributes:
+      label: Error messages
+      description: >
+        Please provide any kind of error output (compilation errors, exception
+        messages, stack traces, etc.) which can help to diagnose the error.
+      render: Shell
+  - type: input
+    id: compiler
+    attributes:
+      label: Compiler and operating system
+      description: >
+        On which operating systems and compilers have you observed the issue?
+        Include as many relevant details about the environment you experienced
+        the bug in. Make sure you use a
+        [supported compiler](https://github.com/nlohmann/json#supported-compilers).
+    validations:
+      required: true
+  - type: input
+    id: version
+    attributes:
+      label: Library version
+      description: >
+        Which version of the library did you use? If it is a released version,
+        please enter the version number (e.g., 3.11.2). Otherwise, please enter
+        the commit hash. If you got the library from another source as the
+        GitHub repository (e.g., via a package manager), please also state
+        this.
+    validations:
+      required: true
+  - type: checkboxes
+    id: validation
+    attributes:
+      label: Validation
+      description: >
+        Please check these additional steps:
+      options:
+        - label: The bug also occurs if the latest version from the [`develop`](https://github.com/nlohmann/json/tree/develop) branch is used.
+        - label: I can successfully [compile and run the unit tests](https://github.com/nlohmann/json#execute-unit-tests).

.github/PULL_REQUEST_TEMPLATE.md

@@ -9,11 +9,11 @@ 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
 
 - The C++11 support varies between different **compilers** and versions. Please note the [list of supported compilers](https://github.com/nlohmann/json/blob/master/README.md#supported-compilers). Some compilers like GCC 4.7 (and earlier), Clang 3.3 (and earlier), or Microsoft Visual Studio 13.0 and earlier are known not to work due to missing or incomplete C++11 support. Please refrain from proposing changes that work around these compiler's limitations with `#ifdef`s or other means.
-- Specifically, I am aware of compilation problems with **Microsoft Visual Studio** (there even is an [issue label](https://github.com/nlohmann/json/issues?utf8=✓&q=label%3A%22visual+studio%22+) for these kind of bugs). I understand that even in 2016, complete C++11 support isn't there yet. But please also understand that I do not want to drop features or uglify the code just to make Microsoft's sub-standard compiler happy. The past has shown that there are ways to express the functionality such that the code compiles with the most recent MSVC - unfortunately, this is not the main objective of the project.
+- Specifically, I am aware of compilation problems with **Microsoft Visual Studio** (there even is an [issue label](https://github.com/nlohmann/json/issues?utf8=✓&q=label%3A%22visual+studio%22+) for this kind of bug). I understand that even in 2016, complete C++11 support isn't there yet. But please also understand that I do not want to drop features or uglify the code just to make Microsoft's sub-standard compiler happy. The past has shown that there are ways to express the functionality such that the code compiles with the most recent MSVC - unfortunately, this is not the main objective of the project.
 - Please refrain from proposing changes that would **break [JSON](https://json.org) conformance**. If you propose a conformant extension of JSON to be supported by the library, please motivate this extension.
 - Please do not open pull requests that address **multiple issues**.