Auto merge of #128506 - compiler-errors:by-move-body, r=cjgillot

Stop storing a special inner body for the coroutine by-move body for async closures

...and instead, just synthesize an item which is treated mostly normally by the MIR pipeline.

This PR does a few things:
* We synthesize a new `DefId` for the by-move body of a closure, which has its `mir_built` fed with the output of the `ByMoveBody` MIR transformation, and some other relevant queries.
* This has the `DefKind::ByMoveBody`, which we use to distinguish it from "real" bodies (that come from HIR) which need to be borrowck'd. Introduce `TyCtxt::is_synthetic_mir` to skip over `mir_borrowck` which is called by `mir_promoted`; borrowck isn't really possible to make work ATM since it heavily relies being called on a body generated from HIR, and is redundant by the construction of the by-move-body.
* Remove the special `PassManager` hacks for handling the inner `by_move_body` stored within the coroutine's mir body. Instead, this body is fed like a regular MIR body, so it's goes through all of the `tcx.*_mir` stages normally (build -> promoted -> ...etc... -> optimized) ✨.
* Remove the `InstanceKind::ByMoveBody` shim, since now we have a "regular" def id, we can just use `InstanceKind::Item`. This also allows us to remove the corresponding hacks from codegen, such as in `fn_sig_for_fn_abi` ✨.

Notable remarks:
* ~~I know it's kind of weird to be using `DefKind::Closure` here, since it's not a distinct closure but just a new MIR body. I don't believe it really matters, but I could also use a different `DefKind`... maybe one that we could use for synthetic MIR bodies in general?~~ edit: We're doing this now.

1 files changed, 9 insertions, 2 deletions

diff --git a/compiler/rustc_hir/src/def.rs b/compiler/rustc_hir/src/def.rs
index 59204d79928..b329432d1e1 100644
--- a/compiler/rustc_hir/src/def.rs
+++ b/compiler/rustc_hir/src/def.rs
@@ -133,6 +133,9 @@ pub enum DefKind {
     /// we treat them all the same, and code which needs to distinguish them can match
     /// or `hir::ClosureKind` or `type_of`.
     Closure,
+    /// The definition of a synthetic coroutine body created by the lowering of a
+    /// coroutine-closure, such as an async closure.
+    SyntheticCoroutineBody,
 }
 
 impl DefKind {
@@ -177,6 +180,7 @@ impl DefKind {
             DefKind::Closure => "closure",
             DefKind::ExternCrate => "extern crate",
             DefKind::GlobalAsm => "global assembly block",
+            DefKind::SyntheticCoroutineBody => "synthetic mir body",
         }
     }
 
@@ -236,7 +240,8 @@ impl DefKind {
             | DefKind::ForeignMod
             | DefKind::GlobalAsm
             | DefKind::Impl { .. }
-            | DefKind::OpaqueTy => None,
+            | DefKind::OpaqueTy
+            | DefKind::SyntheticCoroutineBody => None,
         }
     }
 
@@ -276,6 +281,7 @@ impl DefKind {
             DefKind::GlobalAsm => DefPathData::GlobalAsm,
             DefKind::Impl { .. } => DefPathData::Impl,
             DefKind::Closure => DefPathData::Closure,
+            DefKind::SyntheticCoroutineBody => DefPathData::Closure,
         }
     }
 
@@ -291,7 +297,8 @@ impl DefKind {
             | DefKind::AssocFn
             | DefKind::Ctor(..)
             | DefKind::Closure
-            | DefKind::Static { .. } => true,
+            | DefKind::Static { .. }
+            | DefKind::SyntheticCoroutineBody => true,
             DefKind::Mod
             | DefKind::Struct
             | DefKind::Union