scala3-compiler-bootstrapped/dotty.tools/dotty.tools.dotc/dotty.tools.dotc.transform/dotty.tools.dotc.transform.init/Objects

Objects

dotty.tools.dotc.transform.init.Objects

class Objects(using x$1: Context)

Check initialization safety of static objects

The problem is illustrated by the example below:

class Foo(val opposite: Foo)
case object A extends Foo(B)     // A -> B
case object B extends Foo(A)     // B -> A

In the code above, the initialization of object A depends on B and vice versa. There is no correct way to initialize the code above. The current checker issues a warning for the code above.

At the high-level, the analysis has the following characteristics:

The check enforces the principle of "initialization-time irrelevance", which means that the time when an object is initialized should not change program semantics. For that purpose, it enforces the following rule:
```
The initialization of a static object should not directly or indirectly read or write
mutable state of another static object.
```
This principle not only put initialization of static objects on a solid foundation, but also avoids whole-program analysis.
It is inter-procedural and flow-sensitive.
The check is modular in the sense that each object is checked separately and there is no whole-program analysis. However, the check is not modular in terms of project boundaries.

Attributes

Graph
Supertypes: class Object

trait Matchable

class Any

Members list

Type members

Classlikes

Attributes

Supertypes: trait Serializable

trait Product

trait Equals

class Object

trait Matchable

class Any
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Cache used to terminate the check

Attributes

Supertypes: class Object

trait Matchable

class Any
Self type: Cache.type

Environment for parameters

Attributes

Supertypes: class Object

trait Matchable

class Any
Self type: Env.type

Represents a lambda expression

Value parameters

klass: The enclosing class of the anonymous function's creation site

Attributes

Supertypes: trait Serializable

trait Product

trait Equals

trait ValueElement

trait Value

class Object

trait Matchable

class Any
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Abstract heap for mutable fields

Attributes

Supertypes: class Object

trait Matchable

class Any
Self type: Heap.type

Attributes

Supertypes: class Object

trait Matchable

class Any
Known subtypes: object given_Join_ScopeSet

object given_Join_Value

A reference to a static object

Attributes

Companion: object
Supertypes: trait Serializable

trait Product

trait Equals

class Ref

trait ValueElement

trait Value

class Scope

class Object

trait Matchable

class Any
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Attributes

Companion: class
Supertypes: class Object

trait Matchable

class Any
Self type: ObjectRef.type

Represents arrays.

Note that the 2nd parameter block does not take part in the definition of equality.

Different arrays are distinguished by the context. Currently the default context is the static object whose initialization triggers the creation of the array.

In the future, it is possible that we introduce a mechanism for end-users to mark the context.

Value parameters

owner: The static object whose initialization creates the array.

Attributes

Companion: object
Supertypes: trait Serializable

trait Product

trait Equals

class Ref

trait ValueElement

trait Value

class Scope

class Object

trait Matchable

class Any
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Attributes

Companion: class
Supertypes: class Object

trait Matchable

class Any
Self type: OfArray.type

Represents values that are instances of the specified class.

Note that the 2nd parameter block does not take part in the definition of equality.

Attributes

Companion: object
Supertypes: trait Serializable

trait Product

trait Equals

class Ref

trait ValueElement

trait Value

class Scope

class Object

trait Matchable

class Any
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Attributes

Companion: class
Supertypes: class Object

trait Matchable

class Any
Self type: OfClass.type

Attributes

Companion: object
Supertypes: trait Serializable

trait Product

trait Equals

trait Value

class Object

trait Matchable

class Any
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Attributes

Companion: class
Supertypes: trait Product

trait Mirror

class Object

trait Matchable

class Any
Self type: Package.type

Attributes

Supertypes: trait ValueElement

trait Value

class Scope

class Object

trait Matchable

class Any
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Known subtypes: class ObjectRef

class OfArray

class OfClass

Region context for mutable states

By default, the region context is empty.

Attributes

Supertypes: class Object

trait Matchable

class Any
Self type: Regions.type

Handle return statements in methods and non-local returns in functions.

Attributes

Supertypes: class Object

trait Matchable

class Any
Self type: Returns.type

Represents common base values like Int, String, etc. Assumption: all methods calls on such values should not trigger initialization of global objects or read/write mutable fields

Attributes

Companion: object
Supertypes: trait Serializable

trait Product

trait Equals

trait ValueElement

trait Value

class Object

trait Matchable

class Any
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Attributes

Companion: class
Supertypes: trait Product

trait Mirror

class Object

trait Matchable

class Any
Self type: SafeValue.type

A reference caches the values for outers and immutable fields.

Attributes

Supertypes: class Object

trait Matchable

class Any
Known subtypes: class LocalEnv

class Ref

class ObjectRef

class OfArray

class OfClass

Attributes

Supertypes: trait Serializable

trait Product

trait Equals

class Object

trait Matchable

class Any
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Checking state

Attributes

Supertypes: class Object

trait Matchable

class Any
Self type: State.type

Represents values unknown to the checker, such as values loaded without source

Attributes

Supertypes: trait Singleton

trait Product

trait Mirror

trait Serializable

trait Product

trait Equals

trait ValueElement

trait Value

class Object

trait Matchable

class Any
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Self type: UnknownValue.type

Syntax for the data structure abstraction used in abstract domain:

ve ::= ObjectRef(class) // global object | OfClass(class, ownerObject, ctor, regions) // instance of a class | OfArray(ownerObject, regions) // represents values of native array class in Array.scala | Fun(code, LocalEnv) // value elements that can be contained in ValueSet | SafeValue // values on which method calls and field accesses won't cause warnings. Int, String, etc. | UnknownValue // values whose source are unknown at compile time vs ::= ValueSet(ve) // set of abstract values Bottom ::= ValueSet(Empty) // unreachable code val ::= ve | vs | Package Ref ::= ObjectRef | OfClass | OfArray // values that represent a reference to some (global or instance) object ThisValue ::= Ref | Set(Ref) // possible values for 'this' LocalEnv(meth, ownerObject) // represents environments for methods or functions Scope ::= Ref | LocalEnv ScopeSet ::= Set(Scope)

valsMap = sym -> val // maps variables to their values outersMap = sym -> ScopeSet // maps the possible outer scopes for a corresponding (parent) class heap.MutableData = Scope -> (valsMap, outersMap) // heap is mutable

regions ::= List(sourcePosition)

Attributes

Supertypes: class Object

trait Matchable

class Any
Known subtypes: class Package

trait ValueElement

class Fun

class Ref

class ObjectRef

class OfArray

class OfClass

class SafeValue

object UnknownValue

class ValueSet
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ValueElement are elements that can be contained in a ValueSet

Attributes

Supertypes: trait Value

class Object

trait Matchable

class Any
Known subtypes: class Fun

class Ref

class ObjectRef

class OfArray

class OfClass

class SafeValue

object UnknownValue
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Represents a set of values

It comes from if expressions.

Attributes

Supertypes: trait Serializable

trait Product

trait Equals

trait Value

class Object

trait Matchable

class Any
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Attributes

Supertypes: trait Join[ScopeSet]

class Object

trait Matchable

class Any
Self type: given_Join_ScopeSet.type

Attributes

Supertypes: trait Join[Value]

class Object

trait Matchable

class Any
Self type: given_Join_Value.type

Types

Possible types for 'this'

Attributes

Value members

Concrete methods

Handle assignment lhs.f = rhs.

Value parameters

field: The symbol of the target field.
lhs: The value of the object to be mutated.
rhs: The value to be assigned.
rhsTyp: The type of the right-hand side.

Attributes

Handle method calls e.m(args).

Value parameters

args: Arguments of the method call (all parameter blocks flatten to a list).
meth: The symbol of the target method (could be virtual or abstract method).
needResolve: Whether the target of the call needs resolution?
receiver: The type of the receiver.
superType: The type of the super in a super call. NoType for non-super calls.
value: The value for the receiver.

Attributes

Handle constructor calls <init>(args).

Value parameters

args: Arguments of the constructor call (all parameter blocks flatten to a list).
ctor: The symbol of the target method.
value: The value for the receiver.

Attributes

Handles the evaluation of different expressions

Note: Recursive call should go to eval instead of cases.

Value parameters

expr: The expression to be evaluated.
klass: The enclosing class where the expression expr is located.
thisV: The value for C.this where C is represented by the parameter klass.

Attributes

Evaluate an expression with the given value for this in a given class klass

Note that klass might be a super class of the object referred by thisV. The parameter klass is needed for this resolution. Consider the following code:

class A { A.this class B extends A { A.this } }

As can be seen above, the meaning of the expression A.this depends on where it is located.

This method only handles cache logic and delegates the work to cases.

Value parameters

cacheResult: It is used to reduce the size of the cache.
expr: The expression to be evaluated.
klass: The enclosing class where the expression is located.
thisV: The value for C.this where C is represented by the parameter klass.

Attributes

Evaluate arguments of methods and constructors

Attributes

Evaluate a list of expressions

Attributes

Handle semantics of leaf nodes

For leaf nodes, their semantics is determined by their types.

Value parameters

elideObjectAccess: Whether object access should be omitted. Object access elission happens when the object access is used as a prefix in new o.C and C does not need an outer.
klass: The enclosing class where the type tp is located.
thisV: The value for C.this where C is represented by klass.
tp: The type to be evaluated.

Attributes

Initialize part of an abstract object in klass of the inheritance chain

Value parameters

klass: The class to which the template belongs.
thisV: The value of the current object to be initialized.
tpl: The class body to be evaluated.

Attributes

Handle local variable definition, val x = e or var x = e.

Value parameters

sym: The symbol of the variable.
value: The value of the initializer.

Attributes

Handle new expression new p.C(args). The actual instance might be cached without running the constructor. See tests/init-global/pos/cache-constructor.scala

Value parameters

args: The arguments passsed to the constructor.
ctor: The symbol of the target constructor.
klass: The symbol of the class C.
outer: The value for p.

Attributes

Compute the outer value that corresponds to tref.prefix

Value parameters

klass: The enclosing class where the type tref is located.
thisV: The value for C.this where C is represented by the parameter klass.
tref: The type whose prefix is to be evaluated.

Attributes

Evaluate the cases against the scrutinee value.

It returns the scrutinee in most cases. The main effect of the function is for its side effects of adding bindings to the environment.

See https://docs.scala-lang.org/scala3/reference/changed-features/pattern-matching.html

Value parameters

cases: The cases to match.
klass: The enclosing class where the type tp is located.
scrutinee: The abstract value of the scrutinee.
thisV: The value for C.this where C is represented by klass.

Attributes

Read local variable x.

Value parameters

sym: The symbol of the variable.
thisV: The value for this where the variable is used.

Attributes

Resolve C.this that appear in D.this

Value parameters

elideObjectAccess: Whether object access should be omitted. Object access elision happens when the object access is used as a prefix in new o.C and C does not need an outer.
target: The class symbol for C for which C.this is to be resolved.
thisV: The value for D.this.

Attributes

Resolve C.this by recursively searching through the outer chain

Value parameters

scopeSet: The scopes as the starting point.
target: The class symbol for C for which C.this is to be resolved.

Attributes

Handle selection e.f.

Value parameters

field: The symbol of the target field (could be virtual or abstract).
needResolve: Whether the target of the selection needs resolution?
receiver: The type of the receiver.
value: The value for the receiver.

Attributes

Handle local variable assignmenbt, x = e.

Value parameters

sym: The symbol of the variable.
thisV: The value for this where the assignment locates.
value: The value of the rhs of the assignment.

Attributes

Concrete fields

Check if the checker option reports warnings about unknown code

Attributes

Givens

Extensions

extension (a: Value)

extension [V](map: Map[Symbol, V])(implicit evidence$1: Join[V])

extension (scopes: Iterable[ScopeSet])

extension (values: Iterable[Value])

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