[C++][Pistache] Add compatibility for nlohmann-json 3.5.0

[muttleyxd]

PR checklist

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  @ravinikam @stkrwork @etherealjoy @MartinDelille

Description of the PR

While generated sample downloads nlohmann-json from GitHub, it could also be provided by operating system. Debian 10 Buster provides nlohmann-json3-dev package with 3.5.0 version https://packages.debian.org/buster/nlohmann-json3-dev.

contains was added in 3.6.0 https://github.com/nlohmann/json/releases/tag/v3.6.0

This change makes generated code compatible with 3.5.0.

Here's the code I tested it with:

#include <nlohmann/json.hpp>
#include <iostream>

void check_with_find(char const * const key, nlohmann::json const &json)
{
  if (json.find(key) != json.end())
    std::cout << "find: " << key << " exists!\n";
  else
    std::cout << "find: " << key << " does not exist!\n";
}

void check_with_contains(char const * const key, nlohmann::json const &json)
{
  if (json.contains(key))
    std::cout << "contains: " << key << " exists!\n";
  else
    std::cout << "contains: " << key << " does not exist!\n";
}

int main()
{
  constexpr char const * existing_key = "hello";
  constexpr char const * not_existing_key = "there";

  nlohmann::json json;  
  json[existing_key] = "general";

  check_with_find(existing_key, json);
  check_with_find(not_existing_key, json);
  check_with_contains(existing_key, json);
  check_with_contains(not_existing_key, json);
}

Output:

$ g++ -std=c++17 -Wall -Wextra -pedantic json-find.cpp -o json-find
$ ./json-find
find: hello exists!
find: there does not exist!
contains: hello exists!
contains: there does not exist!

contains is implemented as:

template<typename KeyT>
bool contains(KeyT&& key) const
{
    return is_object() and m_value.object->find(std::forward<KeyT>(key)) != m_value.object->end();
}

So it's almost the same code

[muttleyxd]

How do I restart CI here? CircleCI failed with

--- a/docs/generators/java.md
+++ b/docs/generators/java.md
@@ -55,4 +55,4 @@ sidebar_label: java
 |feignVersion|Version of OpenFeign: '10.x', '9.x' (default)| |false|
 |useReflectionEqualsHashCode|Use org.apache.commons.lang3.builder for equals and hashCode in the models. WARNING: This will fail under a security manager, unless the appropriate permissions are set up correctly and also there's potential performance impact.| |false|
 |caseInsensitiveResponseHeaders|Make API response's headers case-insensitive. Available on okhttp-gson, jersey2 libraries| |false|
-|library|library template (sub-template) to use|<dl><dt>**jersey1**</dt><dd>HTTP client: Jersey client 1.19.x. JSON processing: Jackson 2.8.x. Enable Java6 support using '-DsupportJava6=true'. Enable gzip request encoding using '-DuseGzipFeature=true'. IMPORTANT NOTE: jersey 1.x is no longer actively maintained so please upgrade to 'jersey2' or other HTTP libaries instead.</dd><dt>**jersey2**</dt><dd>HTTP client: Jersey client 2.25.1. JSON processing: Jackson 2.8.x</dd><dt>**feign**</dt><dd>HTTP client: OpenFeign 9.x or 10.x. JSON processing: Jackson 2.8.x. To enable OpenFeign 10.x, set the 'feignVersion' option to '10.x'</dd><dt>**okhttp-gson**</dt><dd>[DEFAULT] HTTP client: OkHttp 3.x. JSON processing: Gson 2.8.x. Enable Parcelable models on Android using '-DparcelableModel=true'. Enable gzip request encoding using '-DuseGzipFeature=true'.</dd><dt>**retrofit**</dt><dd>HTTP client: OkHttp 2.x. JSON processing: Gson 2.x (Retrofit 1.9.0). IMPORTANT NOTE: retrofit1.x is no longer actively maintained so please upgrade to 'retrofit2' instead.</dd><dt>**retrofit2**</dt><dd>HTTP client: OkHttp 3.x. JSON processing: Gson 2.x (Retrofit 2.3.0). Enable the RxJava adapter using '-DuseRxJava[2]=true'. (RxJava 1.x or 2.x)</dd><dt>**resttemplate**</dt><dd>HTTP client: Spring RestTemplate 4.x. JSON processing: Jackson 2.8.x</dd><dt>**webclient**</dt><dd>HTTP client: Spring WebClient 5.x. JSON processing: Jackson 2.9.x</dd><dt>**resteasy**</dt><dd>HTTP client: Resteasy client 3.x. JSON processing: Jackson 2.8.x</dd><dt>**vertx**</dt><dd>HTTP client: VertX client 3.x. JSON processing: Jackson 2.8.x</dd><dt>**google-api-client**</dt><dd>HTTP client: Google API client 1.x. JSON processing: Jackson 2.8.x</dd><dt>**rest-assured**</dt><dd>HTTP client: rest-assured : 3.x. JSON processing: Gson 2.x. Only for Java8</dd><dl>|okhttp-gson|
+|library|library template (sub-template) to use|<dl><dt>**jersey1**</dt><dd>HTTP client: Jersey client 1.19.x. JSON processing: Jackson 2.8.x. Enable Java6 support using '-DsupportJava6=true'. Enable gzip request encoding using '-DuseGzipFeature=true'. IMPORTANT NOTE: jersey 1.x is no longer actively maintained so please upgrade to 'jersey2' or other HTTP libaries instead.</dd><dt>**jersey2**</dt><dd>HTTP client: Jersey client 2.25.1. JSON processing: Jackson 2.8.x</dd><dt>**feign**</dt><dd>HTTP client: OpenFeign 9.x or 10.x. JSON processing: Jackson 2.8.x. To enable OpenFeign 10.x, set the 'feignVersion' option to '10.x'</dd><dt>**okhttp-gson**</dt><dd>[DEFAULT] HTTP client: OkHttp 3.x. JSON processing: Gson 2.8.x. Enable Parcelable models on Android using '-DparcelableModel=true'. Enable gzip request encoding using '-DuseGzipFeature=true'.</dd><dt>**retrofit**</dt><dd>HTTP client: OkHttp 2.x. JSON processing: Gson 2.x (Retrofit 1.9.0). IMPORTANT NOTE: retrofit1.x is no longer actively maintained so please upgrade to 'retrofit2' instead.</dd><dt>**retrofit2**</dt><dd>HTTP client: OkHttp 3.x. JSON processing: Gson 2.x (Retrofit 2.3.0). Enable the RxJava adapter using '-DuseRxJava[2]=true'. (RxJava 1.x or 2.x)</dd><dt>**resttemplate**</dt><dd>HTTP client: Spring RestTemplate 4.x. JSON processing: Jackson 2.8.x</dd><dt>**webclient**</dt><dd>HTTP client: Spring WebClient 5.x. JSON processing: Jackson 2.9.x</dd><dt>**resteasy**</dt><dd>HTTP client: Resteasy client 3.x. JSON processing: Jackson 2.8.x</dd><dt>**vertx**</dt><dd>HTTP client: VertX client 3.x. JSON processing: Jackson 2.8.x</dd><dt>**google-api-client**</dt><dd>HTTP client: Google API client 1.x. JSON processing: Jackson 2.8.x</dd><dt>**rest-assured**</dt><dd>HTTP client: rest-assured : 4.x. JSON processing: Gson 2.x. Only for Java8</dd><dl>|okhttp-gson|
Perform git status
On branch pull/3306
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

	modified:   docs/generators/java.md

no changes added to commit (use "git add" and/or "git commit -a")
Please run 'bin/utils/ensure-up-to-date' locally and commit changes (UNCOMMITTED CHANGES ERROR)
Exited with code 1

I don't think the error is related to my change

[wing328]

@muttleyxd next time you can restart the CI by closing and then reopening the PR.

[wing328]

@muttleyxd thanks for the PR, which has been included in the 4.1.0 release: https://twitter.com/oas_generator/status/1160000504455319553