Re-exports

pub use self::RegionVariableOrigin::*;
pub use self::SubregionOrigin::*;
pub use self::ValuePairs::*;

Modules

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:

combine 🔒

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.

equate 🔒

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.

freshen 🔒

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.

fudge 🔒
glb 🔒

Greatest lower bound. See lattice.

Helper routines for higher-ranked things. See the doc module at the end of the file for details.

Lattice variables

Lexical region resolution.

lub 🔒

Least upper bound. See lattice.

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.

projection 🔒

See README.md.

sub 🔒
undo_log 🔒

Structs

A temporary returned by tcx.infer_ctxt(). This is necessary for multiple InferCtxt to share the same in_progress_typeck_results without using Rc or something similar.

This type contains all the things within InferCtxt that sit within a RefCell and are involved with taking/rolling back snapshots. Snapshot operations are hot enough that we want only one call to borrow_mut per call to start_snapshot and rollback_to.

Replace {integer} with i32 and {float} with f64. Used only for diagnostics.

See the region_obligations field for more information.

The trace designates the path through inference that we took to encounter an error or subtyping constraint.

Enums

Times when we replace late-bound regions with variables:

Reasons to create a region inference variable

The origin of a r1 <= r2 constraint.

Helper for ty_or_const_infer_var_changed (see comment on that), currently used only for traits::fulfill’s list of stalled_on inference variables.

See the error_reporting module for more details.

Traits

Type Definitions