Rollup merge of #67922 - Centril:lowering-cleanup, r=petrochenkov

rustc_ast_lowering: misc cleanup & rustc dep reductions

- The first two commits do some code simplification.
- The next three do some file splitting (getting `lib.rs` below the 3kloc tidy lint).
- The remaining commits reduce the number of `rustc::` imports. This works towards making lowering independent of the `rustc` crate.

r? @oli-obk cc @Zoxc

9 files changed, 8 insertions, 27 deletions

diff --git a/src/librustc/infer/canonical/query_response.rs b/src/librustc/infer/canonical/query_response.rs
index 5e402dc79a1..012900f8af5 100644
--- a/src/librustc/infer/canonical/query_response.rs
+++ b/src/librustc/infer/canonical/query_response.rs
@@ -22,7 +22,7 @@ use crate::traits::{Obligation, ObligationCause, PredicateObligation};
 use crate::ty::fold::TypeFoldable;
 use crate::ty::subst::{GenericArg, GenericArgKind};
 use crate::ty::{self, BoundVar, Ty, TyCtxt};
-use crate::util::captures::Captures;
+use rustc_data_structures::captures::Captures;
 use rustc_index::vec::Idx;
 use rustc_index::vec::IndexVec;
 use rustc_span::DUMMY_SP;
diff --git a/src/librustc/infer/outlives/verify.rs b/src/librustc/infer/outlives/verify.rs
index 0380d0e35e7..8ee8482e79d 100644
--- a/src/librustc/infer/outlives/verify.rs
+++ b/src/librustc/infer/outlives/verify.rs
@@ -3,7 +3,7 @@ use crate::infer::{GenericKind, VerifyBound};
 use crate::traits;
 use crate::ty::subst::{InternalSubsts, Subst};
 use crate::ty::{self, Ty, TyCtxt};
-use crate::util::captures::Captures;
+use rustc_data_structures::captures::Captures;
 use rustc_hir::def_id::DefId;
 
 /// The `TypeOutlives` struct has the job of "lowering" a `T: 'a`
diff --git a/src/librustc/lib.rs b/src/librustc/lib.rs
index 37761c17f52..cf424ffe7b2 100644
--- a/src/librustc/lib.rs
+++ b/src/librustc/lib.rs
@@ -100,7 +100,6 @@ pub mod ty;
 
 pub mod util {
     pub mod bug;
-    pub mod captures;
     pub mod common;
 }
 
diff --git a/src/librustc/middle/cstore.rs b/src/librustc/middle/cstore.rs
index ee43c35c1d0..5b1e7673629 100644
--- a/src/librustc/middle/cstore.rs
+++ b/src/librustc/middle/cstore.rs
@@ -5,8 +5,8 @@
 use crate::hir::map as hir_map;
 use crate::hir::map::definitions::{DefKey, DefPathTable};
 use crate::session::search_paths::PathKind;
-use crate::session::{CrateDisambiguator, Session};
-use crate::ty::{self, TyCtxt};
+use crate::session::CrateDisambiguator;
+use crate::ty::TyCtxt;
 
 use rustc_data_structures::svh::Svh;
 use rustc_data_structures::sync::{self, MetadataRef};
@@ -208,7 +208,6 @@ pub trait CrateStore {
     fn crate_is_private_dep_untracked(&self, cnum: CrateNum) -> bool;
     fn crate_disambiguator_untracked(&self, cnum: CrateNum) -> CrateDisambiguator;
     fn crate_hash_untracked(&self, cnum: CrateNum) -> Svh;
-    fn item_generics_cloned_untracked(&self, def: DefId, sess: &Session) -> ty::Generics;
 
     // This is basically a 1-based range of ints, which is a little
     // silly - I may fix that.
diff --git a/src/librustc/traits/project.rs b/src/librustc/traits/project.rs
index 79e1b6444a9..738bbd936fe 100644
--- a/src/librustc/traits/project.rs
+++ b/src/librustc/traits/project.rs
@@ -17,7 +17,6 @@ use crate::infer::{InferCtxt, InferOk, LateBoundRegionConversionTime};
 use crate::ty::fold::{TypeFoldable, TypeFolder};
 use crate::ty::subst::{InternalSubsts, Subst};
 use crate::ty::{self, ToPolyTraitRef, ToPredicate, Ty, TyCtxt};
-use crate::util::common::FN_OUTPUT_NAME;
 use rustc_data_structures::snapshot_map::{Snapshot, SnapshotMap};
 use rustc_hir::def_id::DefId;
 use rustc_macros::HashStable;
@@ -1364,7 +1363,7 @@ fn confirm_callable_candidate<'cx, 'tcx>(
         projection_ty: ty::ProjectionTy::from_ref_and_name(
             tcx,
             trait_ref,
-            Ident::with_dummy_span(FN_OUTPUT_NAME),
+            Ident::with_dummy_span(rustc_hir::FN_OUTPUT_NAME),
         ),
         ty: ret_type,
     });
diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index 2f51d21d24c..d1e37a4ea11 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -26,8 +26,8 @@ use crate::ty::layout::VariantIdx;
 use crate::ty::subst::{InternalSubsts, Subst, SubstsRef};
 use crate::ty::util::{Discr, IntTypeExt};
 use crate::ty::walk::TypeWalker;
-use crate::util::captures::Captures;
 use arena::SyncDroplessArena;
+use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
diff --git a/src/librustc/ty/sty.rs b/src/librustc/ty/sty.rs
index aeda2eb1a15..c89d045cebb 100644
--- a/src/librustc/ty/sty.rs
+++ b/src/librustc/ty/sty.rs
@@ -13,11 +13,10 @@ use crate::ty::layout::VariantIdx;
 use crate::ty::subst::{GenericArg, GenericArgKind, InternalSubsts, Subst, SubstsRef};
 use crate::ty::{self, AdtDef, DefIdTree, Discr, Ty, TyCtxt, TypeFlags, TypeFoldable};
 use crate::ty::{List, ParamEnv, ParamEnvAnd, TyS};
-use crate::util::captures::Captures;
+use polonius_engine::Atom;
+use rustc_data_structures::captures::Captures;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
-
-use polonius_engine::Atom;
 use rustc_index::vec::Idx;
 use rustc_macros::HashStable;
 use rustc_span::symbol::{kw, Symbol};
diff --git a/src/librustc/util/captures.rs b/src/librustc/util/captures.rs
deleted file mode 100644
index 26b90ebfd5f..00000000000
--- a/src/librustc/util/captures.rs
+++ /dev/null
@@ -1,10 +0,0 @@
-/// "Signaling" trait used in impl trait to tag lifetimes that you may
-/// need to capture but don't really need for other reasons.
-/// Basically a workaround; see [this comment] for details.
-///
-/// [this comment]: https://github.com/rust-lang/rust/issues/34511#issuecomment-373423999
-// FIXME(eddyb) false positive, the lifetime parameter is "phantom" but needed.
-#[allow(unused_lifetimes)]
-pub trait Captures<'a> {}
-
-impl<'a, T: ?Sized> Captures<'a> for T {}
diff --git a/src/librustc/util/common.rs b/src/librustc/util/common.rs
index 95746852157..9324b26a09b 100644
--- a/src/librustc/util/common.rs
+++ b/src/librustc/util/common.rs
@@ -5,14 +5,9 @@ use rustc_data_structures::sync::Lock;
 use std::fmt::Debug;
 use std::time::{Duration, Instant};
 
-use rustc_span::symbol::{sym, Symbol};
-
 #[cfg(test)]
 mod tests;
 
-// The name of the associated type for `Fn` return types.
-pub const FN_OUTPUT_NAME: Symbol = sym::Output;
-
 pub use errors::ErrorReported;
 
 pub fn to_readable_str(mut val: usize) -> String {