Module Refinements

INTERNAL: This is an internal library; its interface may change without notice.

Provides classes for working with variable refinements.

Variable refinements are expressions that appear in a guard node (such as an if condition) and can be used to refine the information derived about a variable by the flow analysis. Each refinement only refines a single variable, and only certain simple constructs are considered (primarily typeof expressions and comparisons).

To perform the refinement, the expression is evaluated to a RefinementValue, which is a more fine-grained version of AbstractValue that distinguishes individual constants value. This evaluation takes place in a context that restricts the value of the refined variable to a single candidate value, which is one of the AbstractValues that the flow analysis infers for it.

If the expression evaluates to a refinement value that represents true, then the candidate value passes the refinement. Hence, it can be propagated across a condition guard with outcome true.

Conversely, if it evaluates to false, the candidate value can be propagated across a condition guard with outcome false.

Note that, like all abstract values, refinement values are overapproximations, so the refinement can evaluate to both true and false for the same candidate value.