Sniffs

Before version 5.4, PHP CompatInfo and its compatibility analyser was monolithic code.

Since version 5.4, PHP CompatInfo used a sniff architecture that simplify maintainability of existing code and allows to extend it more easily.

Each sniff, is in charge to detect a PHP language feature. Here is the list of features supported and their corresponding sniffs :

PHP 5.0

Sniff category	Sniff class name	PHP Feature
Classes	MethodDeclarationSniff	Method Visibility
Classes	PropertyDeclarationSniff	Properties

Sniff category	Sniff class name	PHP Feature
Classes	MagicMethodsSniff	Magic Methods

Sniff category	Sniff class name	PHP Feature

Sniff category	Sniff class name	PHP Feature
Classes	MagicMethodsSniff	Magic Methods
Classes	DynamicAccessSniff	Dynamic Static Method access
Classes	DynamicAccessSniff	Dynamic Static Property access
ControlStructures	DeclareSniff	Declare
ControlStructures	GotoSniff	Goto
FunctionDeclarations	ClosureSniff	Anonymous functions
	`VersionResolverVisitor`	Closures
Operators	ShortTernaryOperatorSniff	Ternary Operator
	`VersionResolverVisitor`	Namespaces
TextProcessing	CryptStringSniff	CRYPT_BLOWFISH security fix details

Sniff category	Sniff class name	PHP Feature
Arrays	ArrayDereferencingSyntaxSniff	Array dereferencing
Arrays	ShortArraySyntaxSniff	Short array syntax
Classes	ClassMemberAccessSniff	Class member access on instantiation
Expressions	ClassExprSyntaxSniff	Class::{expr}() syntax
Numbers	BinaryNumberFormatSniff	Binary number format
UseDeclarations	UseTraitSniff	Traits
	`VersionResolverVisitor`	Traits

Sniff category	Sniff class name	PHP Feature
Constants	MagicClassConstantSniff	::class syntax
Expressions	EmptySniff	empty() supports arbitrary expressions
Generators	GeneratorSniff	Generators

Sniff category	Sniff class name	PHP Feature
FunctionDeclarations	ParamTypeDeclarationSniff	Scalar type declarations
FunctionDeclarations	ReturnTypeDeclarationSniff	Return type declarations
Keywords	ReservedSniff	Scalar type declarations
Operators	NullCoalesceOperatorSniff	Null coalescing operator
Operators	CombinedComparisonOperatorSniff	Spaceship operator
		Constant arrays using define()
Classes	AnonymousClassSniff	Anonymous classes
Classes	ClassMemberAccessSniff	Class member access on cloning
ControlStructures	DeclareSniff	Declare
Generators	GeneratorSniff	Generator Return Expressions
Generators	GeneratorSniff	Generator Delegation

Sniff category	Sniff class name	PHP Feature
FunctionDeclarations	ParamTypeDeclarationSniff	Nullable types
FunctionDeclarations	ReturnTypeDeclarationSniff	Nullable types
FunctionDeclarations	ReturnTypeDeclarationSniff	Void functions
		Symmetric array destructuring
		Class constant visibility
FunctionDeclarations	ParamTypeDeclarationSniff	iterable pseudo-type
Keywords	ReservedSniff	iterable pseudo-type
		Multi catch exception handling
		Support for keys in list()

Sniff category	Sniff class name	PHP Feature
Keywords	ReservedSniff	New object type

Sniff category	Sniff class name	PHP Feature
FunctionCalls	SameSiteCookieSniff	SetCookie accept $options argument

Sniff category	Sniff class name	PHP Feature
Arrays	ArrayUnpackingSyntaxSniff	Array unpacking support for numeric-keyed arrays
Classes	TypedPropertySniff	Typed properties
FunctionDeclarations	ArrowFunctionSniff	Arrow functions
	`VersionResolverVisitor`	Arrow functions

Sniff category	Sniff class name	PHP Feature
Attributes	AttributeSniff	Attributes
Classes	PropertyPromotionSniff	Constructor property promotion
ControlStructures	MatchSniff	Match expressions
ControlStructures	NonCapturingCatchSniff	Non-capturing catches
FunctionDeclarations	NamedArgumentDeclarationSniff	Named arguments
FunctionDeclarations	ParamTypeDeclarationSniff	Union types
FunctionDeclarations	TrailingCommaSniff	Trailing comma
Operators	NullsafeOperatorSniff	Nullsafe operator

Sniff category	Sniff class name	PHP Feature
Arrays	ArrayUnpackingSyntaxSniff	Array unpacking support for string-keyed arrays
Classes	ReadonlyPropertySniff	Readonly Properties
Classes	NewInitializerSniff	New initializers
Constants	ClassConstantSniff	Final class constants
Enumerations	EnumerationSniff	Enumerations
Fibers	FiberSniff	Fibers
FunctionDeclarations	FirstClassCallableSniff	First class callable
FunctionDeclarations	ParamTypeDeclarationSniff	Pure Intersection Types
FunctionDeclarations	ReturnTypeDeclarationSniff	Pure Intersection Types
FunctionDeclarations	ReturnTypeDeclarationSniff	Never return type
Numbers	OctalNumberFormatSniff	Explicit Octal numeral notation

Sniff category	Sniff class name	PHP Feature
Attributes	AllowDynamicPropertiesAttributeSniff	AllowDynamicProperties attribute
Attributes	SensitiveParameterAttributeSniff	SensitiveParameter attribute
Classes	ReadonlyClassSniff	Readonly Classes
Constants	ConstantsInTraitsSniff	Constants in Traits
FunctionDeclarations	ParamTypeDeclarationSniff	Disjunctive Normal Form Types
FunctionDeclarations	ReturnTypeDeclarationSniff	Allow null, false, and true as stand-alone types
TextProcessing	DeprecateDollarBraceStringInterpolationSniff	Deprecated \${} string interpolation

Sniff category	Sniff class name	PHP Feature
Attributes	OverrideAttributeSniff	Override attribute
Constants	DynamicClassConstantFetchSniff	Dynamic Class Constant fetch syntax
Constants	TypedClassConstantSniff	Typed Class Constants
Expressions	StaticVarInitializerSniff	Static Variable initializers

Namespaces declaration have no sniff, because its detected by the VersionResolverVisitor
Classes declaration have no sniff, because its detected by the VersionResolverVisitor
Interfaces declaration have no sniff, because its detected by the VersionResolverVisitor
Traits declaration have no sniff, because its detected by the VersionResolverVisitor
Closures are initialized by the VersionResolverVisitor and keywords (this, self, parent, static) are detected with ClosureSniff
Arrow functions have no sniff, because its detected by the VersionResolverVisitor, but has its test case with ArrowFunctionSniffTest