org.eclipse.jdt.internal.compiler.lookup

Class InferenceContext18

java.lang.Object

org.eclipse.jdt.internal.compiler.lookup.InferenceContext18

public class InferenceContext18
extends Object

Main class for new type inference as per JLS8 sect 18. Keeps contextual state and drives the algorithm.

Inference Basics

• 18.1.1 Inference variables: InferenceVariable
• 18.1.2 Constraint Formulas: subclasses of ConstraintFormula
• 18.1.3 Bounds: TypeBound
  Capture bounds are directly captured in BoundSet.captures, throws-bounds in BoundSet.inThrows.
  Also: BoundSet: main state during inference.

Each instance of InferenceContext18 manages instances of the above and coordinates the inference process.

Queries and utilities

• TypeBinding.isProperType(boolean): used to exclude "types" that mention inference variables (18.1.1).
• TypeBinding.mentionsAny(TypeBinding[], int): does the receiver type binding mention any of the given types?
• TypeBinding.substituteInferenceVariable(InferenceVariable, TypeBinding): replace occurrences of an inference variable with a proper type.
• TypeBinding.collectInferenceVariables(Set): collect all inference variables mentioned in the receiver type into the given set.
• TypeVariableBinding.getTypeBounds(InferenceVariable, InferenceSubstitution): Compute the initial type bounds for one inference variable as per JLS8 sect 18.1.3.

Phases of Inference

• 18.2 Reduction: reduce() with most work happening in implementations of ConstraintFormula.reduce(InferenceContext18):
  • 18.2.1 Expression Compatibility Constraints: ConstraintExpressionFormula.reduce(InferenceContext18).
  • 18.2.2 Type Compatibility Constraints ff. ConstraintTypeFormula.reduce(InferenceContext18).
• 18.3 Incorporation: BoundSet.incorporate(InferenceContext18); during inference new constraints are accepted via BoundSet.reduceOneConstraint(InferenceContext18, ConstraintFormula) (combining 18.2 & 18.3)
• 18.4 Resolution: resolve(InferenceVariable[]).

Some of the above operations accumulate their results into currentBounds, whereas the last phase returns the resulting bound set while keeping the previous state in currentBounds.

18.5. Uses of Inference

These are the main entries from the compiler into the inference engine:

18.5.1 Invocation Applicability Inference

inferInvocationApplicability(MethodBinding, TypeBinding[], boolean). Prepare the initial state for inference of a generic invocation - no target type used at this point. Need to call solve() afterwards to produce the intermediate result.
Called indirectly from Scope.findMethod(ReferenceBinding, char[], TypeBinding[], InvocationSite, boolean) et al to select applicable methods into overload resolution.

18.5.2 Invocation Type Inference

inferInvocationType(BoundSet, TypeBinding, InvocationSite, MethodBinding). After a most specific method has been picked, and given a target type determine the final generic instantiation. As long as a target type is still unavailable this phase keeps getting deferred.
Different wrappers exist for the convenience of different callers.

18.5.3 Functional Interface Parameterization Inference

Controlled from LambdaExpression.resolveType(BlockScope).

18.5.4 More Specific Method Inference

Not Yet Implemented

For 18.5.1 and 18.5.2 some high-level control is implemented in ParameterizedGenericMethodBinding.computeCompatibleMethod(MethodBinding, TypeBinding[], Scope, InvocationSite, int).

Inference Lifecycle

The separation into 18.5.1 and 18.5.2 causes some complexity:

• Calling both parts of inference is directly interwoven with overload resolution. See PGMB#computeCompatibleMethod() for the basic protocol.
• Intermediate state regarding inference must be stored between both phases. Inference is performed with different inputs for each pair of Invocation x ParameterizedGenericMethodBinding, see Invocation.registerInferenceContext() and getInferenceContext().
  As part of the lifecycle state, each instance of InferenceContext18 remembers the current inferenceKind and stepCompleted.
• Nested inference/resolving: If an invocation argument is a poly expression itself, final resolving of the argument can only happened after Invocation Type Inference regarding the outer invocation. Outer inference must produce the target type that drives the inner inference / resolving. Two different protocols are applied:
  • If the inner poly expression is an invocation, inner inference is directly incorporated into the currentBounds, see block inside ConstraintExpressionFormula.reduce(InferenceContext18).
    In this case the results of the combined inference need to be applied to all contained inner invocations, which happens in rebindInnerPolies(BoundSet, TypeBinding[]), which must be called whenever 18.5.2 finishes.
  • If the inner poly expression is a functional expression or a conditional expression no inference variables exist representing the inner. In this case the final target type is pushed into the inner using Expression.checkAgainstFinalTargetType(TypeBinding, Scope), which, too, is called from rebindInnerPolies(BoundSet, TypeBinding[]).
  • For recursively pushing target types into arguments of an invocation method ASTNode.resolvePolyExpressionArguments(Invocation, MethodBinding, TypeBinding[], Scope) exists, which is called in two situations: (1) for non-generic outer invocations from MessageSend#findMethodBinding() and Statement#findConstructorBinding(); (2) for generic outer invocations from rebindInnerPolies(BoundSet, TypeBinding[]).
  • In some situations invocation arguments that are poly invocations need to be resolved in the middle of overload resolution to answer Scope.parameterCompatibilityLevel18(org.eclipse.jdt.internal.compiler.lookup.MethodBinding, org.eclipse.jdt.internal.compiler.lookup.TypeBinding[], boolean, org.eclipse.jdt.internal.compiler.lookup.InvocationSite) (where the outer invocation did not involve any inference).
    
  Pushing inference results into an inner invocation happens using Invocation.updateBindings(MethodBinding,TypeBinding).
• Decision whether or not an invocation is a variable-arity invocation is made by first attempting to solve 18.5.1 in mode CHECK_LOOSE. Only if that fails, another attempt is made in mode CHECK_VARARG. Which of these two attempts was successful is stored in inferenceKind. This field must be consulted whenever arguments of an invocation should be further processed. See also getParameter(TypeBinding[], int, boolean) and its clients.

Field Summary

Fields

Modifier and Type	Field and Description
static int	APPLICABILITY_INFERRED Applicability Inference (18.5.1) has been completed.
static int	BINDINGS_UPDATED All nested elements have been fully resolved.
static int	CHECK_LOOSE
static int	CHECK_STRICT
static int	CHECK_VARARG
List<org.eclipse.jdt.internal.compiler.lookup.ConstraintFormula>	constraintsWithUncheckedConversion Signals whether any type compatibility makes use of unchecked conversion.
static int	NOT_INFERRED
InferenceContext18	outerContext Link to an outer inference context, used for bundled error reporting.
int	stepCompleted Marks how much work has been done so far? Used to avoid performing any of these tasks more than once.
static int	TYPE_INFERRED Invocation Type Inference (18.5.2) has been completed (for some target type).

Constructor Summary

Constructors

Constructor and Description
InferenceContext18(Scope scope)
InferenceContext18(Scope scope, Expression[] arguments, InvocationSite site) Construct an inference context for an invocation (method/constructor).

Method Summary

Modifier and Type	Method and Description
void	addProblemMethod(ProblemMethodBinding problemMethod)
void	addThrowsContraints(TypeBinding[] parameters, InferenceVariable[] variables, ReferenceBinding[] thrownExceptions) JLS 18.1.3 Bounds: throws α: the inference variable α appears in a throws clause
InferenceVariable[]	addTypeVariableSubstitutions(TypeBinding[] typeVariables) Add new inference variables for the given type variables.
InferenceVariable[]	createInitialBoundSet(TypeVariableBinding[] typeParameters) JLS 18.1.3: Create initial bounds from a given set of type parameters declarations.
void	createInitialConstraintsForParameters(TypeBinding[] parameters, boolean checkVararg, TypeBinding varArgsType, MethodBinding method) JLS 18.5.1: compute bounds from formal and actual parameters.
org.eclipse.jdt.internal.compiler.lookup.InferenceContext18.SuspendedInferenceRecord	enterLambda(LambdaExpression lambda)
org.eclipse.jdt.internal.compiler.lookup.InferenceContext18.SuspendedInferenceRecord	enterPolyInvocation(InvocationSite invocation, Expression[] innerArguments)
TypeBinding[]	getFunctionInterfaceArgumentSolutions(TypeBinding[] a)
static TypeBinding	getParameter(TypeBinding[] parameters, int rank, boolean isVarArgs) Retrieve the rank'th parameter, possibly respecting varargs invocation, see 15.12.2.4.
MethodBinding	getReturnProblemMethodIfNeeded(TypeBinding expectedType, MethodBinding method) Create a problem method signaling failure of invocation type inference, unless the given candidate is tolerable to be compatible with buggy javac.
TypeBinding[]	getSolutions(TypeVariableBinding[] typeParameters, InvocationSite site, org.eclipse.jdt.internal.compiler.lookup.BoundSet boundSet) Retrieve the resolved solutions for all given type variables.
boolean	hasResultFor(TypeBinding targetType)
ReferenceBinding	inferFunctionalInterfaceParameterization(LambdaExpression lambda, BlockScope blockScope, ParameterizedTypeBinding targetTypeWithWildCards) 18.5.3 Functional Interface Parameterization Inference
void	inferInvocationApplicability(MethodBinding method, TypeBinding[] arguments, boolean isDiamond) JLS 18.5.1 Invocation Applicability Inference.
org.eclipse.jdt.internal.compiler.lookup.BoundSet	inferInvocationType(org.eclipse.jdt.internal.compiler.lookup.BoundSet b1, TypeBinding expectedType, InvocationSite invocationSite, MethodBinding method) JLS 18.5.2 Invocation Type Inference
MethodBinding	inferInvocationType(Invocation invocation, ParameterizedGenericMethodBinding method) Simplified API to perform Invocation Type Inference (JLS 18.5.2) and perform subsequent steps: bound check, rebinding of inner poly expressions, and creating of a problem method binding if needed.
boolean	isMoreSpecificThan(MethodBinding m1, MethodBinding m2, boolean isVarArgs, boolean isVarArgs2) 18.5.4 More Specific Method Inference
boolean	isResolved(org.eclipse.jdt.internal.compiler.lookup.BoundSet boundSet) Have all inference variables been instantiated successfully?
boolean	isVarArgs()
static void	missingImplementation(String msg)
static ParameterizedTypeBinding	parameterizedWithWildcard(TypeBinding type) If 'type' is a parameterized type and one of its arguments is a wildcard answer the casted type, else null.
void	rebindInnerPolies(org.eclipse.jdt.internal.compiler.lookup.BoundSet bounds, TypeBinding[] parameterTypes) After inference has finished, iterate all inner poly expressions (Invocations), that have been included in the inference.
boolean	rebindInnerPolies(MethodBinding method, InvocationSite site)
void	recordUncheckedConversion(org.eclipse.jdt.internal.compiler.lookup.ConstraintTypeFormula constraint) Record the fact that the given constraint requires unchecked conversion.
boolean	reduceAndIncorporate(org.eclipse.jdt.internal.compiler.lookup.ConstraintFormula constraint) When inference produces a new constraint, reduce it to a suitable type bound and add the latter to the bound set.
boolean	reduceWithEqualityConstraints(TypeBinding[] p, TypeBinding[] q)
boolean	registerSolution(TypeBinding targetType, MethodBinding updatedBinding)
void	reportInvalidInvocation(Invocation invocation, MethodBinding binding)
void	resumeSuspendedInference(org.eclipse.jdt.internal.compiler.lookup.InferenceContext18.SuspendedInferenceRecord record)
org.eclipse.jdt.internal.compiler.lookup.BoundSet	solve() Try to solve the inference problem defined by constraints and bounds previously registered.
org.eclipse.jdt.internal.compiler.lookup.BoundSet	solve(InferenceVariable[] toResolve)
TypeBinding	substitute(TypeBinding type) Substitute any type variables mentioned in 'type' by the corresponding inference variable, if one exists.
String	toString()
boolean	usesUncheckedConversion() For use by 15.12.2.6 Method Invocation Type

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

stepCompleted

public int stepCompleted

Marks how much work has been done so far? Used to avoid performing any of these tasks more than once.

NOT_INFERRED

public static final int NOT_INFERRED

See Also:

Constant Field Values

APPLICABILITY_INFERRED

public static final int APPLICABILITY_INFERRED

Applicability Inference (18.5.1) has been completed.

See Also:

Constant Field Values

TYPE_INFERRED

public static final int TYPE_INFERRED

Invocation Type Inference (18.5.2) has been completed (for some target type).

See Also:

Constant Field Values

BINDINGS_UPDATED

public static final int BINDINGS_UPDATED

All nested elements have been fully resolved.

See Also:

Constant Field Values

constraintsWithUncheckedConversion

public List<org.eclipse.jdt.internal.compiler.lookup.ConstraintFormula> constraintsWithUncheckedConversion

Signals whether any type compatibility makes use of unchecked conversion.

outerContext

public InferenceContext18 outerContext

Link to an outer inference context, used for bundled error reporting.

CHECK_STRICT

public static final int CHECK_STRICT

See Also:

Constant Field Values

CHECK_LOOSE

public static final int CHECK_LOOSE

See Also:

Constant Field Values

CHECK_VARARG

public static final int CHECK_VARARG

See Also:

Constant Field Values

Constructor Detail

InferenceContext18

public InferenceContext18(Scope scope,
                          Expression[] arguments,
                          InvocationSite site)

Construct an inference context for an invocation (method/constructor).

InferenceContext18

public InferenceContext18(Scope scope)

Method Detail

createInitialBoundSet

public InferenceVariable[] createInitialBoundSet(TypeVariableBinding[] typeParameters)

JLS 18.1.3: Create initial bounds from a given set of type parameters declarations.

Returns:

the set of inference variables created for the given typeParameters

substitute

public TypeBinding substitute(TypeBinding type)

Substitute any type variables mentioned in 'type' by the corresponding inference variable, if one exists.

createInitialConstraintsForParameters

public void createInitialConstraintsForParameters(TypeBinding[] parameters,
                                                  boolean checkVararg,
                                                  TypeBinding varArgsType,
                                                  MethodBinding method)

JLS 18.5.1: compute bounds from formal and actual parameters.

addTypeVariableSubstitutions

public InferenceVariable[] addTypeVariableSubstitutions(TypeBinding[] typeVariables)

Add new inference variables for the given type variables.

addThrowsContraints

public void addThrowsContraints(TypeBinding[] parameters,
                                InferenceVariable[] variables,
                                ReferenceBinding[] thrownExceptions)

JLS 18.1.3 Bounds: throws α: the inference variable α appears in a throws clause

inferInvocationApplicability

public void inferInvocationApplicability(MethodBinding method,
                                         TypeBinding[] arguments,
                                         boolean isDiamond)

JLS 18.5.1 Invocation Applicability Inference.

inferInvocationType

public org.eclipse.jdt.internal.compiler.lookup.BoundSet inferInvocationType(org.eclipse.jdt.internal.compiler.lookup.BoundSet b1,
                                                                             TypeBinding expectedType,
                                                                             InvocationSite invocationSite,
                                                                             MethodBinding method)
                                                                      throws InferenceFailureException

JLS 18.5.2 Invocation Type Inference

Callers are responsible for any post-processing (see rebindInnerPolies(BoundSet, TypeBinding[])).

Parameters:

b1 - "the bound set produced by reduction in order to demonstrate that m is applicable in 18.5.1"

Throws:

InferenceFailureException

inferInvocationType

public MethodBinding inferInvocationType(Invocation invocation,
                                         ParameterizedGenericMethodBinding method)

Simplified API to perform Invocation Type Inference (JLS 18.5.2) and perform subsequent steps: bound check, rebinding of inner poly expressions, and creating of a problem method binding if needed. Should only be called if the inference has not yet finished. Version used for inner invocations, where argument types need to be extracted from actual invocation arguments.

Parameters:

invocation - invocation being inferred

method - current candidate method binding for this invocation

Returns:

a valid method binding with updated type parameters, or a problem method binding signaling either inference failure or a bound mismatch.

hasResultFor

public boolean hasResultFor(TypeBinding targetType)

registerSolution

public boolean registerSolution(TypeBinding targetType,
                                MethodBinding updatedBinding)

inferFunctionalInterfaceParameterization

public ReferenceBinding inferFunctionalInterfaceParameterization(LambdaExpression lambda,
                                                                 BlockScope blockScope,
                                                                 ParameterizedTypeBinding targetTypeWithWildCards)

18.5.3 Functional Interface Parameterization Inference

reduceWithEqualityConstraints

public boolean reduceWithEqualityConstraints(TypeBinding[] p,
                                             TypeBinding[] q)

isMoreSpecificThan

public boolean isMoreSpecificThan(MethodBinding m1,
                                  MethodBinding m2,
                                  boolean isVarArgs,
                                  boolean isVarArgs2)

18.5.4 More Specific Method Inference

solve

public org.eclipse.jdt.internal.compiler.lookup.BoundSet solve()
                                                        throws InferenceFailureException

Try to solve the inference problem defined by constraints and bounds previously registered.

Returns:

a bound set representing the solution, or null if inference failed

Throws:

InferenceFailureException - a compile error has been detected during inference

solve

public org.eclipse.jdt.internal.compiler.lookup.BoundSet solve(InferenceVariable[] toResolve)
                                                        throws InferenceFailureException

Throws:

InferenceFailureException

isResolved

public boolean isResolved(org.eclipse.jdt.internal.compiler.lookup.BoundSet boundSet)

Have all inference variables been instantiated successfully?

getSolutions

public TypeBinding[] getSolutions(TypeVariableBinding[] typeParameters,
                                  InvocationSite site,
                                  org.eclipse.jdt.internal.compiler.lookup.BoundSet boundSet)

Retrieve the resolved solutions for all given type variables.

Parameters:

typeParameters -

boundSet - where instantiations are to be found

Returns:

array containing the substituted types or null elements for any type variable that could not be substituted.

reduceAndIncorporate

public boolean reduceAndIncorporate(org.eclipse.jdt.internal.compiler.lookup.ConstraintFormula constraint)
                             throws InferenceFailureException

When inference produces a new constraint, reduce it to a suitable type bound and add the latter to the bound set.

Throws:

InferenceFailureException

enterPolyInvocation

public org.eclipse.jdt.internal.compiler.lookup.InferenceContext18.SuspendedInferenceRecord enterPolyInvocation(InvocationSite invocation,
                                                                                                                Expression[] innerArguments)

enterLambda

public org.eclipse.jdt.internal.compiler.lookup.InferenceContext18.SuspendedInferenceRecord enterLambda(LambdaExpression lambda)

resumeSuspendedInference

public void resumeSuspendedInference(org.eclipse.jdt.internal.compiler.lookup.InferenceContext18.SuspendedInferenceRecord record)

rebindInnerPolies

public boolean rebindInnerPolies(MethodBinding method,
                                 InvocationSite site)

rebindInnerPolies

public void rebindInnerPolies(org.eclipse.jdt.internal.compiler.lookup.BoundSet bounds,
                              TypeBinding[] parameterTypes)

After inference has finished, iterate all inner poly expressions (Invocations), that have been included in the inference. For each of these update some type information from the inference result and perhaps trigger follow-up resolving as needed. Similar for poly expressions that did not directly participate in the inference but are direct arguments of the current invocation (FunctionalExpression, ConditionalExpression).

isVarArgs

public boolean isVarArgs()

getParameter

public static TypeBinding getParameter(TypeBinding[] parameters,
                                       int rank,
                                       boolean isVarArgs)

Retrieve the rank'th parameter, possibly respecting varargs invocation, see 15.12.2.4. Returns null if out of bounds and CHECK_VARARG was not requested. Precondition: isVarArgs implies method.isVarargs()

getReturnProblemMethodIfNeeded

public MethodBinding getReturnProblemMethodIfNeeded(TypeBinding expectedType,
                                                    MethodBinding method)

Create a problem method signaling failure of invocation type inference, unless the given candidate is tolerable to be compatible with buggy javac.

reportInvalidInvocation

public void reportInvalidInvocation(Invocation invocation,
                                    MethodBinding binding)

toString

public String toString()

Overrides:

toString in class Object

addProblemMethod

public void addProblemMethod(ProblemMethodBinding problemMethod)

parameterizedWithWildcard

public static ParameterizedTypeBinding parameterizedWithWildcard(TypeBinding type)

If 'type' is a parameterized type and one of its arguments is a wildcard answer the casted type, else null. A nonnull answer is ensured to also have nonnull arguments.

getFunctionInterfaceArgumentSolutions

public TypeBinding[] getFunctionInterfaceArgumentSolutions(TypeBinding[] a)

recordUncheckedConversion

public void recordUncheckedConversion(org.eclipse.jdt.internal.compiler.lookup.ConstraintTypeFormula constraint)

Record the fact that the given constraint requires unchecked conversion.

usesUncheckedConversion

public boolean usesUncheckedConversion()

For use by 15.12.2.6 Method Invocation Type

missingImplementation

public static void missingImplementation(String msg)