Satisfy tidy checks

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Oliver Schneider 2018-07-06 14:25:34 +02:00 committed by Who? Me?!
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commit 1a5993b9ca
3 changed files with 24 additions and 23 deletions

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# The HIR
The HIR "High-Level Intermediate Representation" is the primary IR used in
most of rustc. It is a compiler-friendly representation of the abstract syntax
tree (AST) that is generated after parsing, macro expansion, and name
The HIR "High-Level Intermediate Representation" is the primary IR used
in most of rustc. It is a compiler-friendly representation of the abstract
syntax tree (AST) that is generated after parsing, macro expansion, and name
resolution (see [Lowering](./lowering.md) for how the HIR is created).
Many parts of HIR resemble Rust surface syntax quite closely, with
the exception that some of Rust's expression forms have been desugared away. For
example, `for` loops are converted into a `loop` and do not appear in the HIR.
This makes HIR more amenable to analysis than a normal AST.
the exception that some of Rust's expression forms have been desugared away.
For example, `for` loops are converted into a `loop` and do not appear in
the HIR. This makes HIR more amenable to analysis than a normal AST.
This chapter covers the main concepts of the HIR.

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* `if let`
* Converted to `match`
* Universal `impl Trait`
* Converted to generic arguments (but with some flags, to know that the user didn't write them)
* Converted to generic arguments
(but with some flags, to know that the user didn't write them)
* Existential `impl Trait`
* Converted to a virtual `existential type` declaration
@ -34,14 +35,14 @@ sanity checks in `src/librustc/hir/map/hir_id_validator.rs`:
which produces both a new `NodeId` as well as automatically lowering it
for you so you also get the `HirId`.
If you are creating new `DefId`s, since each `DefId` needs to have a corresponding
`NodeId`, it is adviseable to add these `NodeId`s to the `AST` so you don't have
to generate new ones during lowering. This has the advantage of creating a
way to find the `DefId` of something via its `NodeId`. If lowering needs this
`DefId` in multiple places, you can't generate a new `NodeId` in all those places
because you'd also get a new `DefId` then. With a `NodeId` from the `AST` this is
not an issue.
If you are creating new `DefId`s, since each `DefId` needs to have a
corresponding `NodeId`, it is adviseable to add these `NodeId`s to the
`AST` so you don't have to generate new ones during lowering. This has
the advantage of creating a way to find the `DefId` of something via its
`NodeId`. If lowering needs this `DefId` in multiple places, you can't
generate a new `NodeId` in all those places because you'd also get a new
`DefId` then. With a `NodeId` from the `AST` this is not an issue.
Having the `NodeId` also allows the `DefCollector` to generate the `DefId`s instead
of lowering having to do it on the fly. Centralizing the `DefId` generation in one
place makes it easier to refactor and reason about.
Having the `NodeId` also allows the `DefCollector` to generate the `DefId`s
instead of lowering having to do it on the fly. Centralizing the `DefId`
generation in one place makes it easier to refactor and reason about.

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## Scopes and ribs
A name is visible only in certain area in the source code. This forms a
hierarchical structure, but not necessarily a simple one if one scope is part
of another, it doesn't mean the name visible in the outer one is also visible in
the inner one, or that it refers to the same thing.
hierarchical structure, but not necessarily a simple one if one scope is
part of another, it doesn't mean the name visible in the outer one is also
visible in the inner one, or that it refers to the same thing.
To cope with that, the compiler introduces the concept of Ribs. This is
abstraction of a scope. Every time the set of visible names potentially changes,
@ -54,9 +54,9 @@ example:
When searching for a name, the stack of ribs is traversed from the innermost
outwards. This helps to find the closest meaning of the name (the one not
shadowed by anything else). The transition to outer rib may also change the
rules what names are usable if there are nested functions (not closures), the
inner one can't access parameters and local bindings of the outer one, even
though they should be visible by ordinary scoping rules. An example:
rules what names are usable if there are nested functions (not closures),
the inner one can't access parameters and local bindings of the outer one,
even though they should be visible by ordinary scoping rules. An example:
```rust
fn do_something<T: Default>(val: T) { // <- New rib in both types and values (1)