Opis JSON Schema validation for PHP 7.0 (#76)

This PR adds a PHP 7.0-compatible a version of the
[Opis](https://opis.io/json-schema/2.x/) JSON Schema validator.

Opis seems to be the most complete and well-maintained JSON Schema
validator for PHP. However,
Blueprints aim for PHP 7.0+ support and Opis is not compatible with PHP
7.0. Therefore, it was
transpiled to PHP 7.0 with [rector](https://github.com/rectorphp/rector)
and provided here.

See #75 for more
context.

cc @reimic

.github/workflows/ci.yml

@@ -3,7 +3,7 @@ name: CI
 on:
   push:
     branches:
-    - trunk
+      - trunk
   pull_request:
 
 jobs:
@@ -25,15 +25,10 @@ jobs:
       - name: Install Dependencies
         run: composer install --no-interaction --prefer-dist --optimize-autoloader
 
-      - name: Check PHP version compatibility
-        uses: pantheon-systems/phpcompatibility-action@v1
-        with:
-          skip-php-setup: true
-          test-versions: 7.4-
-          paths: ${{ github.workspace }}/src
+      - name: PHPCS checks
+        run: ./vendor/bin/phpcs ${{ github.workspace }}/src
 
   test-unit:
-    needs: [php-cs-check]
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: true

README.md

@@ -91,15 +91,30 @@ vendor/bin/phpunit --testdox
 ### Regenerate models files from JSON schema with
 
 ```shell
- php src/WordPress/Blueprints/bin/autogenerate_models.php
+composer global require jane-php/json-schema
+php src/WordPress/Blueprints/bin/autogenerate_models.php
 ```
 
 ## Building to .phar
 
-The Blueprints library is distributed as a .phar library. To build the .phar file, run:
+The Blueprints library is distributed as a .phar library. To build the .phar file, install box:
 
 ```shell
-vendor/bin/box compile
+composer global require humbug/box
+```
+
+And then run:
+
+```shell
+rm composer.lock
+rm -rf vendor
+COMPOSER=composer-web.json composer install --no-dev
+rm -rf vendor/pimple/pimple/ext/
+rm -rf vendor/symfony/*/*.md
+rm -rf vendor/symfony/*/composer.json
+rm -rf vendor/symfony/*/*.dist
+rm -rf vendor/*/*/LICENSE
+box compile
 ```
 
 Note that in box.json, the `"check-requirements"` option is set to `false`. Somehow, keeping it as `true` results in a
@@ -112,6 +127,53 @@ To try the built .phar file, run:
 rm -rf new-wp/* && USE_PHAR=1 php blueprint_compiling.php
 ```
 
+## PHP 7.0 Compatibility
+
+This project is compatible with PHP >= 7.0.
+
+Part of the process is automated with [rector](https://github.com/rectorphp/rector),
+which transpiles the features added in PHP 7.2 and later to PHP 7.1. Unfortunately,
+that's as far as Rector goes.
+
+From there, manual transformations are required to bring the compatibility further down to PHP 7.0.
+
+### Automated part
+
+To transpile the code to PHP 7.1, run:
+
+```bash
+# Install rector:
+composer require rector/rector --ignore-platform-req=php
+
+# Transpile:
+php vendor/bin/rector process src
+```
+
+Unfortunately, Rector does not support downgrading to PHP 7.0 yet, so we need to do the
+last stretch manually.
+
+### Manual part
+
+Rector will downgrade PHP code to PHP 7.1 but not further. We need PHP 7.0 compat
+so here's a few additional regexps to run. Regexps are not, of course, reliable in
+the general case, but they seem to do the trick here.
+
+List of manual replacements
+
+* `: \?[a-zA-Z_0-9]+` -> (empty string) to remove the unsupported return type
+  from `function(): ?SchemaResolver {}` -> `function() {}`.
+* `: iterable` to fix `Fatal error: Generators may only declare a return type of Generator, Iterator or Traversable`.
+* `\?[a-zA-Z_0-9]+ \$` -> `$` to remove the unsupported nullable type from function signatures,
+  e.g. `function(?Schema $schema){}` -> `function($schema){}`.
+* `(protected|public|private) const` -> `const` as const visibility is not supported in PHP 7.0.
+* `: void` -> `` as `void` return type is unsupported in PHP 7.0.
+
+@TODO:
+
+* `[$ns, $name] = $this->parseName($name);` -> `list($ns, $name) = $this->parseName($name);`
+* `foreach ($data as [$cp, $chars]) {` -> `foreach ($data as list($cp, $chars)) {`
+* Find or write Rector rules for downgrading to PHP 7.0
+
 ## License
 
 WordPress Blueprints are open-source software licensed under the GPL.

composer.json

@@ -6,9 +6,7 @@
     "symfony/process": "*",
     "pimple/pimple": "*",
     "psr/simple-cache": "*",
-    "opis/json-schema": "*",
-    "ext-json": "*",
-    "nikic/php-parser": "v4.18.0"
+    "ext-json": "*"
   },
   "require-dev": {
     "phpunit/phpunit": "*",
@@ -36,7 +34,10 @@
     ],
     "psr-4": {
       "WordPress\\": "src/WordPress",
-      "Symfony\\Component\\Process\\": "vendor/symfony/process"
+      "Symfony\\Component\\Process\\": "vendor/symfony/process",
+      "Opis\\JsonSchema\\": "src/opis/json-schema/src",
+      "Opis\\String\\": "src/opis/string/src",
+      "Opis\\Uri\\": "src/opis/uri/src"
     },
     "files": [
       "src/WordPress/Blueprints/functions.php",