A nice interface for working with the infcx. The basic idea is to
do infcx.at(cause, param_env), which sets the “cause” of the
operation as well as the surrounding parameter environment. Then
you can do something like .sub(a, b) or .eq(a, b) to create a
subtype or equality relationship respectively. The first argument
is always the “expected” output from the POV of diagnostics.
Canonicalization is the key to constructing a query in the
middle of type inference. Ordinarily, it is not possible to store
types from type inference in query keys, because they contain
references to inference variables whose lifetimes are too short
and so forth. Canonicalizing a value T1 using canonicalize_query
produces two things:
There are four type combiners:
Equate,
Sub,
Lub, and
Glb.
Each implements the trait
TypeRelation and contains methods for
combining two instances of various things and yielding a new instance.
These combiner methods always yield a
Result<T>. To relate two
types, you can use
infcx.at(cause, param_env) which then allows
you to use the relevant methods of
At.
Error Reporting Code for the inference engine
This module handles the relationships between “free regions”, i.e., lifetime parameters.
Ordinarily, free regions are unrelated to one another, but they can be related via implied
or explicit bounds. In that case, we track the bounds using the TransitiveRelation type,
and use that to decide when one free region outlives another, and so forth.
Freshening is the process of replacing unknown variables with fresh types. The idea is that
the type, after freshening, contains no inference variables but instead contains either a
value for each variable or fresh “arbitrary” types wherever a variable would have been.
Helper routines for higher-ranked things. See the doc module at
the end of the file for details.
Lattice variables
Lexical region resolution.
This code is kind of an alternate way of doing subtyping,
supertyping, and type equating, distinct from the combine.rs
code but very similar in its effect and design. Eventually the two
ought to be merged. This code is intended for use in NLL and chalk.
Various code related to computing outlives relations.
See README.md.