feature #32669 [Yaml] Add flag to dump NULL as ~ (OskarStark)

This PR was merged into the 4.4 branch.

Discussion
----------

[Yaml] Add flag to dump NULL as ~

| Q             | A
| ------------- | ---
| Branch?       | 4.4
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #...   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | https://github.com/symfony/symfony-docs/pull/12071

This PR adds the ability to dump `null` as `~` by a new Flag `Yaml::DUMP_NULL_AS_TILDE`:
```diff
- foo: null
+ foo: ~
```

Todos:
- [x] Fix/add tests

Commits
-------

749c11d94c [Yaml] Add flag to dump NULL as ~

src/Symfony/Component/Yaml/CHANGELOG.md

@@ -1,6 +1,11 @@
 CHANGELOG
 =========
 
+4.4.0
+-----
+
+ * Added support to dump `null` as `~` by using the `Yaml::DUMP_NULL_AS_TILDE` flag.
+
 4.3.0
 -----
 

src/Symfony/Component/Yaml/Inline.php

@@ -33,6 +33,7 @@ class Inline
     private static $objectSupport = false;
     private static $objectForMap = false;
     private static $constantSupport = false;
+    private static $nullAsTilde = false;
 
     /**
      * @param int         $flags
@@ -45,6 +46,7 @@ class Inline
         self::$objectSupport = (bool) (Yaml::PARSE_OBJECT & $flags);
         self::$objectForMap = (bool) (Yaml::PARSE_OBJECT_FOR_MAP & $flags);
         self::$constantSupport = (bool) (Yaml::PARSE_CONSTANT & $flags);
+        self::$nullAsTilde = (bool) (Yaml::DUMP_NULL_AS_TILDE & $flags);
         self::$parsedFilename = $parsedFilename;
 
         if (null !== $parsedLineNumber) {
@@ -129,7 +131,7 @@ class Inline
                     throw new DumpException(sprintf('Unable to dump PHP resources in a YAML file ("%s").', get_resource_type($value)));
                 }
 
-                return 'null';
+                return self::dumpNull($flags);
             case $value instanceof \DateTimeInterface:
                 return $value->format('c');
             case \is_object($value):
@@ -155,11 +157,11 @@ class Inline
                     throw new DumpException('Object support when dumping a YAML file has been disabled.');
                 }
 
-                return 'null';
+                return self::dumpNull($flags);
             case \is_array($value):
                 return self::dumpArray($value, $flags);
             case null === $value:
-                return 'null';
+                return self::dumpNull($flags);
             case true === $value:
                 return 'true';
             case false === $value:
@@ -256,6 +258,15 @@ class Inline
         return sprintf('{ %s }', implode(', ', $output));
     }
 
+    private static function dumpNull(int $flags): string
+    {
+        if (Yaml::DUMP_NULL_AS_TILDE & $flags) {
+            return '~';
+        }
+
+        return 'null';
+    }
+
     /**
      * Parses a YAML scalar.
      *

src/Symfony/Component/Yaml/Tests/DumperTest.php

@@ -504,6 +504,11 @@ YAML;
         $this->expectExceptionMessage('The indentation must be greater than zero');
         new Dumper(-4);
     }
+
+    public function testDumpNullAsTilde()
+    {
+        $this->assertSame('{ foo: ~ }', $this->dumper->dump(['foo' => null], 0, 0, Yaml::DUMP_NULL_AS_TILDE));
+    }
 }
 
 class A

src/Symfony/Component/Yaml/Yaml.php

@@ -33,6 +33,7 @@ class Yaml
     const PARSE_CONSTANT = 256;
     const PARSE_CUSTOM_TAGS = 512;
     const DUMP_EMPTY_ARRAY_AS_SEQUENCE = 1024;
+    const DUMP_NULL_AS_TILDE = 2048;
 
     /**
      * Parses a YAML file into a PHP value.