Refactor HIR places

[arora-aman]

Discussion: https://rust-lang.zulipchat.com/#narrow/stream/189812-t-compiler.2Fwg-rfc-2229/topic/refactoring.20.60hir.3A.3APlace.60.20and.20.60hir_id.60

• Investigate usage of usage of hir_id of hir::Place and confirm it is only being used for error reporting.

The current suggestion is to

• Refactor code and rename Place to PlaceReference
• Reintroduce Place except hir_id and span are not part of Place anymore
• Modify PlaceReference so it looks something like this:

struct PlaceReference {
    hir_id: HirId,
    span: Span,
    place: Place,
}

• Replace PlaceReference to Place if it does not need hir_id and span

Place documentation

[roxelo]

The current suggestion is to

• Refactor code and rename Place to PlaceReference
• Reintroduce Place except hir_id and span are not part of Place anymore
• Modify PlaceReference so it looks something like this:

struct PlaceReference {
    hir_id: HirId,
    span: Span,
    place: Place,
}

• Replace PlaceReference to Place if it does not need hir_id and span

Place documentation

First step is to look at the usage of hir_id of hir::Place and confirm it is only being used for error reporting.

[arora-aman]

Within librustc_typchk, HirPlace is referred as mc::Place outside it is referred toi as rustc_typeck::expr_use_visitor::Place.

Easiest way I could think of was to check for files where expr_use_visitor::Place was being included.

1. rg "expr_use.*\*", Search for patterns like "expr_use<anything>* to match for an include all from expr_use_visitor, returned nothing.
2. rg "\bexpr.*\bPlace\b". \b is used to mark a word boundry. So this will allow patterns like expr_use_visitior::Place but not someexprPlace. The intent was to search for lines like expr_use_visitor{Place

Removing results from within typchk and some extra unintended matches we have:

librustc_mir_build/build/expr/as_place.rs
69:    crate fn as_place<M>(&mut self, mut block: BasicBlock, expr: M) -> BlockAnd<Place<'tcx>>

librustc_mir_build/build/expr/into.rs
398:                debug_assert!(Category::of(&expr.kind) == Some(Category::Place));
406:                debug_assert!(Category::of(&expr.kind) == Some(Category::Place));
415:                debug_assert!(Category::of(&expr.kind) == Some(Category::Place));

tools/clippy/clippy_lints/src/escape.rs
9:use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, Place, PlaceBase};

tools/clippy/clippy_lints/src/loops.rs
31:use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, Place, PlaceBase};

tools/clippy/clippy_lints/src/utils/usage.rs
11:use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, Place, PlaceBase};

MIR relies on hir::Expr for lowering and not HirPlace (thanks to Matthew Jaspeer) so we are left with

tools/clippy/clippy_lints/src/escape.rs
9:use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, Place, PlaceBase};

tools/clippy/clippy_lints/src/loops.rs
31:use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, Place, PlaceBase};

tools/clippy/clippy_lints/src/utils/usage.rs
11:use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, Place, PlaceBase};

More info on ripgrep/rg: https://github.com/sexxi-goose/internal_fydp_documentation/wiki/Dev-Setup#searching-the-codebase