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Rollup merge of #100256 - camelid:typeck-ctxt-doc, r=compiler-errors

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Add some high-level docs to `FnCtxt` and `ItemCtxt`

I haven't understood the difference between these before, but
``@compiler-errors`` helped me clear it up. Hopefully this will help other
people who've been confused!

r? `@compiler-errors`
This commit is contained in:
Matthias Krüger 2022-08-10 00:00:31 +02:00 committed by GitHub
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2 changed files with 32 additions and 1 deletions
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11
compiler/rustc_typeck/src/check/fn_ctxt/mod.rs
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@ -26,6 +26,17 @@ use rustc_trait_selection::traits::{ObligationCause, ObligationCauseCode};
use std::cell::{Cell, RefCell};
use std::ops::Deref;
/// The `FnCtxt` stores type-checking context needed to type-check bodies of
/// functions, closures, and `const`s, including performing type inference
/// with [`InferCtxt`].
///
/// This is in contrast to [`ItemCtxt`], which is used to type-check item *signatures*
/// and thus does not perform type inference.
///
/// See [`ItemCtxt`]'s docs for more.
///
/// [`ItemCtxt`]: crate::collect::ItemCtxt
/// [`InferCtxt`]: infer::InferCtxt
pub struct FnCtxt<'a, 'tcx> {
pub(super) body_id: hir::HirId,

22
compiler/rustc_typeck/src/collect.rs
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@ -94,7 +94,27 @@ pub fn provide(providers: &mut Providers) {
///////////////////////////////////////////////////////////////////////////
/// Context specific to some particular item. This is what implements
/// `AstConv`. It has information about the predicates that are defined
/// [`AstConv`].
///
/// # `ItemCtxt` vs `FnCtxt`
///
/// `ItemCtxt` is primarily used to type-check item signatures and lower them
/// from HIR to their [`ty::Ty`] representation, which is exposed using [`AstConv`].
/// It's also used for the bodies of items like structs where the body (the fields)
/// are just signatures.
///
/// This is in contrast to [`FnCtxt`], which is used to type-check bodies of
/// functions, closures, and `const`s -- anywhere that expressions and statements show up.
///
/// An important thing to note is that `ItemCtxt` does no inference -- it has no [`InferCtxt`] --
/// while `FnCtxt` does do inference.
///
/// [`FnCtxt`]: crate::check::FnCtxt
/// [`InferCtxt`]: rustc_infer::infer::InferCtxt
///
/// # Trait predicates
///
/// `ItemCtxt` has information about the predicates that are defined
/// on the trait. Unfortunately, this predicate information is
/// available in various different forms at various points in the
/// process. So we can't just store a pointer to e.g., the AST or the