Module visit

The Stable MIR Visitor

Overview

We currently only support an immutable visitor. The structure of this visitor is similar to the ones internal to rustc, and it follows the following conventions:

For every mir item, the trait has a visit_<item> and a super_<item> method.

• visit_<item>, by default, calls super_<item>
• super_<item>, by default, destructures the <item> and calls visit_<sub_item> for all sub-items that compose the original item.

In order to implement a visitor, override the visit_* methods for the types you are interested in analyzing, and invoke (within that method call) self.super_* to continue to the traverse. Avoid calling super methods in other circumstances.

For the most part, we do not destructure things external to the MIR, e.g., types, spans, etc, but simply visit them and stop. This avoids duplication with other visitors like TypeFoldable.

Updating

The code is written in a very deliberate style intended to minimize the chance of things being overlooked.

Use pattern matching to reference fields and ensure that all matches are exhaustive.

For this to work, ALL MATCHES MUST BE EXHAUSTIVE IN FIELDS AND VARIANTS. That means you never write .. to skip over fields, nor do you write _ to skip over variants in a match.

The only place that _ is acceptable is to match a field (or variant argument) that does not require visiting.

Structs

• Location
  The location of a statement / terminator in the code and the CFG.
• PlaceContext
  Information about a place’s usage.
• PlaceRef
  Reference to a place used to represent a partial projection.

Traits

• MirVisitor

Functions

• statement_location
  Location of the statement at the given index for a given basic block. Assumes that stmt_idx and bb_idx are valid for a given body.
• terminator_location
  Location of the terminator for a given basic block. Assumes that bb_idx is valid for a given body.
• visit_opaque 🔒
  This function is a no-op that gets used to ensure this visitor is kept up-to-date.