From 5deec307f70135d83839e98c64495f91d776bc27 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jesper=20Steen=20M=C3=B8ller?= <jesper@selskabet.org>
Date: Tue, 30 Apr 2019 15:59:29 +0200
Subject: [PATCH 01/10] Fix #45268 by saving all NodeId's for resolved traits.

---
 Cargo.lock                                    | 16 +++++-
 src/librustc/hir/mod.rs                       |  9 +++-
 src/librustc/ich/impls_hir.rs                 | 21 ++++----
 src/librustc_resolve/Cargo.toml               |  1 +
 src/librustc_resolve/lib.rs                   | 41 ++++++++--------
 src/librustc_typeck/check/method/mod.rs       |  6 +--
 src/librustc_typeck/check/method/probe.rs     | 32 ++++++------
 .../lint/unused_import_warning_issue_45268.rs | 49 +++++++++++++++++++
 .../unused_import_warning_issue_45268.stderr  | 12 +++++
 9 files changed, 137 insertions(+), 50 deletions(-)
 create mode 100644 src/test/ui/lint/unused_import_warning_issue_45268.rs
 create mode 100644 src/test/ui/lint/unused_import_warning_issue_45268.stderr

diff --git a/Cargo.lock b/Cargo.lock
index 7823c377b2ad8..f8dd4c91773be 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -296,6 +296,18 @@ dependencies = [
  "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "cargo_metadata"
+version = "0.6.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "error-chain 0.12.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "semver 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.82 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_derive 1.0.81 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_json 1.0.33 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "cargo_metadata"
 version = "0.7.1"
@@ -1612,7 +1624,7 @@ name = "miri"
 version = "0.1.0"
 dependencies = [
  "byteorder 1.2.7 (registry+https://github.com/rust-lang/crates.io-index)",
- "cargo_metadata 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cargo_metadata 0.6.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "colored 1.6.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "compiletest_rs 0.3.22 (registry+https://github.com/rust-lang/crates.io-index)",
  "directories 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2957,6 +2969,7 @@ dependencies = [
  "rustc_data_structures 0.0.0",
  "rustc_errors 0.0.0",
  "rustc_metadata 0.0.0",
+ "smallvec 0.6.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "syntax 0.0.0",
  "syntax_pos 0.0.0",
 ]
@@ -4066,6 +4079,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum byteorder 1.2.7 (registry+https://github.com/rust-lang/crates.io-index)" = "94f88df23a25417badc922ab0f5716cc1330e87f71ddd9203b3a3ccd9cedf75d"
 "checksum bytes 0.4.11 (registry+https://github.com/rust-lang/crates.io-index)" = "40ade3d27603c2cb345eb0912aec461a6dec7e06a4ae48589904e808335c7afa"
 "checksum bytesize 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "716960a18f978640f25101b5cbf1c6f6b0d3192fab36a2d98ca96f0ecbe41010"
+"checksum cargo_metadata 0.6.4 (registry+https://github.com/rust-lang/crates.io-index)" = "e5d1b4d380e1bab994591a24c2bdd1b054f64b60bef483a8c598c7c345bc3bbe"
 "checksum cargo_metadata 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)" = "585784cac9b05c93a53b17a0b24a5cdd1dfdda5256f030e089b549d2390cc720"
 "checksum cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)" = "5e5f3fee5eeb60324c2781f1e41286bdee933850fff9b3c672587fed5ec58c83"
 "checksum cfg-if 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)" = "082bb9b28e00d3c9d39cc03e64ce4cea0f1bb9b3fde493f0cbc008472d22bdf4"
diff --git a/src/librustc/hir/mod.rs b/src/librustc/hir/mod.rs
index ae7358df9d8fa..8ef5b24a9f279 100644
--- a/src/librustc/hir/mod.rs
+++ b/src/librustc/hir/mod.rs
@@ -37,6 +37,7 @@ use rustc_macros::HashStable;
 use serialize::{self, Encoder, Encodable, Decoder, Decodable};
 use std::collections::{BTreeSet, BTreeMap};
 use std::fmt;
+use smallvec::SmallVec;
 
 /// HIR doesn't commit to a concrete storage type and has its own alias for a vector.
 /// It can be `Vec`, `P<[T]>` or potentially `Box<[T]>`, or some other container with similar
@@ -2505,10 +2506,16 @@ pub type FreevarMap = NodeMap<Vec<Freevar<ast::NodeId>>>;
 
 pub type CaptureModeMap = NodeMap<CaptureClause>;
 
+pub type SmallHirIdVec = SmallVec<[HirId;1]>;
+pub type SmallNodeIdVec = SmallVec<[NodeId;1]>;
+
+ // The TraitCandidate's import_ids is empty if the trait is defined in the same module, and
+ // has length > 0 if the trait is found through an chain of imports, starting with the
+ // import/use statement in the scope where the trait is used.
 #[derive(Clone, Debug)]
 pub struct TraitCandidate {
     pub def_id: DefId,
-    pub import_id: Option<NodeId>,
+    pub import_ids: SmallNodeIdVec,
 }
 
 // Trait method resolution
diff --git a/src/librustc/ich/impls_hir.rs b/src/librustc/ich/impls_hir.rs
index 65795d2b136b4..eb57f08003ced 100644
--- a/src/librustc/ich/impls_hir.rs
+++ b/src/librustc/ich/impls_hir.rs
@@ -391,13 +391,14 @@ impl<'a> HashStable<StableHashingContext<'a>> for hir::TraitCandidate {
                                           hcx: &mut StableHashingContext<'a>,
                                           hasher: &mut StableHasher<W>) {
         hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
-            let hir::TraitCandidate {
+            let &hir::TraitCandidate {
                 def_id,
-                import_id,
-            } = *self;
+                import_ids,
+            } = &self;
 
             def_id.hash_stable(hcx, hasher);
-            import_id.hash_stable(hcx, hasher);
+            // We only use the outermost import NodeId as key
+            import_ids.first().hash_stable(hcx, hasher);
         });
     }
 }
@@ -410,13 +411,13 @@ impl<'a> ToStableHashKey<StableHashingContext<'a>> for hir::TraitCandidate {
                           -> Self::KeyType {
         let hir::TraitCandidate {
             def_id,
-            import_id,
-        } = *self;
+            import_ids,
+        } = self;
 
-        let import_id = import_id.map(|node_id| hcx.node_to_hir_id(node_id))
-                                 .map(|hir_id| (hcx.local_def_path_hash(hir_id.owner),
-                                                hir_id.local_id));
-        (hcx.def_path_hash(def_id), import_id)
+        let import_ids = import_ids.first().map(|node_id| hcx.node_to_hir_id(*node_id))
+                                           .map(|hir_id| (hcx.local_def_path_hash(hir_id.owner),
+                                                          hir_id.local_id));
+        (hcx.def_path_hash(*def_id), import_ids)
     }
 }
 
diff --git a/src/librustc_resolve/Cargo.toml b/src/librustc_resolve/Cargo.toml
index 836b4ad38ca88..968a45e241e84 100644
--- a/src/librustc_resolve/Cargo.toml
+++ b/src/librustc_resolve/Cargo.toml
@@ -20,3 +20,4 @@ errors = { path = "../librustc_errors", package = "rustc_errors" }
 syntax_pos = { path = "../libsyntax_pos" }
 rustc_data_structures = { path = "../librustc_data_structures" }
 rustc_metadata = { path = "../librustc_metadata" }
+smallvec = { version = "0.6.7", features = ["union", "may_dangle"] }
diff --git a/src/librustc_resolve/lib.rs b/src/librustc_resolve/lib.rs
index e0892f98d3147..71721504d5add 100644
--- a/src/librustc_resolve/lib.rs
+++ b/src/librustc_resolve/lib.rs
@@ -17,6 +17,7 @@ pub use rustc::hir::def::{Namespace, PerNS};
 
 use GenericParameters::*;
 use RibKind::*;
+use smallvec::smallvec;
 
 use rustc::hir::map::{Definitions, DefCollector};
 use rustc::hir::{self, PrimTy, Bool, Char, Float, Int, Uint, Str};
@@ -28,7 +29,7 @@ use rustc::hir::def::{
 };
 use rustc::hir::def::Namespace::*;
 use rustc::hir::def_id::{CRATE_DEF_INDEX, LOCAL_CRATE, DefId};
-use rustc::hir::{Freevar, FreevarMap, TraitCandidate, TraitMap, GlobMap};
+use rustc::hir::{Freevar, FreevarMap, TraitCandidate, TraitMap, GlobMap, SmallNodeIdVec};
 use rustc::ty::{self, DefIdTree};
 use rustc::util::nodemap::{NodeMap, NodeSet, FxHashMap, FxHashSet, DefIdMap};
 use rustc::{bug, span_bug};
@@ -4582,7 +4583,7 @@ impl<'a> Resolver<'a> {
                 module.span,
             ).is_ok() {
                 let def_id = module.def_id().unwrap();
-                found_traits.push(TraitCandidate { def_id: def_id, import_id: None });
+                found_traits.push(TraitCandidate { def_id: def_id, import_ids: smallvec![] });
             }
         }
 
@@ -4641,37 +4642,35 @@ impl<'a> Resolver<'a> {
                     false,
                     module.span,
                 ).is_ok() {
-                    let import_id = match binding.kind {
-                        NameBindingKind::Import { directive, .. } => {
-                            self.maybe_unused_trait_imports.insert(directive.id);
-                            self.add_to_glob_map(&directive, trait_name);
-                            Some(directive.id)
-                        }
-                        _ => None,
-                    };
+                    let import_ids = self.find_transitive_imports(&binding.kind, &trait_name);
                     let trait_def_id = module.def_id().unwrap();
-                    found_traits.push(TraitCandidate { def_id: trait_def_id, import_id });
+                    found_traits.push(TraitCandidate { def_id: trait_def_id, import_ids });
                 }
             } else if let Res::Def(DefKind::TraitAlias, _) = binding.res() {
                 // For now, just treat all trait aliases as possible candidates, since we don't
                 // know if the ident is somewhere in the transitive bounds.
-
-                let import_id = match binding.kind {
-                    NameBindingKind::Import { directive, .. } => {
-                        self.maybe_unused_trait_imports.insert(directive.id);
-                        self.add_to_glob_map(&directive, trait_name);
-                        Some(directive.id)
-                    }
-                    _ => None,
-                };
+                let import_ids = self.find_transitive_imports(&binding.kind, &trait_name);
                 let trait_def_id = binding.res().def_id();
-                found_traits.push(TraitCandidate { def_id: trait_def_id, import_id });
+                found_traits.push(TraitCandidate { def_id: trait_def_id, import_ids });
             } else {
                 bug!("candidate is not trait or trait alias?")
             }
         }
     }
 
+    fn find_transitive_imports(&mut self, kind: &NameBindingKind<'_>,
+                               trait_name: &Ident) -> SmallNodeIdVec {
+        let mut import_ids = smallvec![];
+        let mut kind = kind;
+        while let NameBindingKind::Import { directive, binding, .. } = *kind {
+            self.maybe_unused_trait_imports.insert(directive.id);
+            self.add_to_glob_map(&directive, *trait_name);
+            import_ids.push(directive.id);
+            kind = &binding.kind;
+        };
+        import_ids
+    }
+
     fn lookup_import_candidates_from_module<FilterFn>(&mut self,
                                           lookup_ident: Ident,
                                           namespace: Namespace,
diff --git a/src/librustc_typeck/check/method/mod.rs b/src/librustc_typeck/check/method/mod.rs
index bbdc7df4441e8..a4b1687ea5301 100644
--- a/src/librustc_typeck/check/method/mod.rs
+++ b/src/librustc_typeck/check/method/mod.rs
@@ -195,8 +195,8 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
             ProbeScope::TraitsInScope
         )?;
 
-        if let Some(import_id) = pick.import_id {
-            let import_def_id = self.tcx.hir().local_def_id_from_hir_id(import_id);
+        for import_id in &pick.import_ids {
+            let import_def_id = self.tcx.hir().local_def_id_from_hir_id(*import_id);
             debug!("used_trait_import: {:?}", import_def_id);
             Lrc::get_mut(&mut self.tables.borrow_mut().used_trait_imports)
                 .unwrap().insert(import_def_id);
@@ -434,7 +434,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         let pick = self.probe_for_name(span, probe::Mode::Path, method_name, IsSuggestion(false),
                                        self_ty, expr_id, ProbeScope::TraitsInScope)?;
         debug!("resolve_ufcs: pick={:?}", pick);
-        if let Some(import_id) = pick.import_id {
+        for import_id in pick.import_ids {
             let import_def_id = tcx.hir().local_def_id_from_hir_id(import_id);
             debug!("resolve_ufcs: used_trait_import: {:?}", import_def_id);
             Lrc::get_mut(&mut self.tables.borrow_mut().used_trait_imports)
diff --git a/src/librustc_typeck/check/method/probe.rs b/src/librustc_typeck/check/method/probe.rs
index 8c61a127d1014..148b7d5edb570 100644
--- a/src/librustc_typeck/check/method/probe.rs
+++ b/src/librustc_typeck/check/method/probe.rs
@@ -7,6 +7,7 @@ use crate::check::autoderef::{self, Autoderef};
 use crate::check::FnCtxt;
 use crate::hir::def_id::DefId;
 use crate::hir::def::DefKind;
+use crate::hir::SmallHirIdVec;
 use crate::namespace::Namespace;
 
 use rustc_data_structures::sync::Lrc;
@@ -35,6 +36,8 @@ use std::mem;
 use std::ops::Deref;
 use std::cmp::max;
 
+use smallvec::smallvec;
+
 use self::CandidateKind::*;
 pub use self::PickKind::*;
 
@@ -121,7 +124,7 @@ struct Candidate<'tcx> {
     xform_ret_ty: Option<Ty<'tcx>>,
     item: ty::AssociatedItem,
     kind: CandidateKind<'tcx>,
-    import_id: Option<hir::HirId>,
+    import_ids: SmallHirIdVec,
 }
 
 #[derive(Debug)]
@@ -146,7 +149,7 @@ enum ProbeResult {
 pub struct Pick<'tcx> {
     pub item: ty::AssociatedItem,
     pub kind: PickKind<'tcx>,
-    pub import_id: Option<hir::HirId>,
+    pub import_ids: hir::SmallHirIdVec,
 
     // Indicates that the source expression should be autoderef'd N times
     //
@@ -716,7 +719,7 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
             self.push_candidate(Candidate {
                 xform_self_ty, xform_ret_ty, item,
                 kind: InherentImplCandidate(impl_substs, obligations),
-                import_id: None
+                import_ids: smallvec![]
             }, true);
         }
     }
@@ -750,7 +753,7 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
             this.push_candidate(Candidate {
                 xform_self_ty, xform_ret_ty, item,
                 kind: ObjectCandidate,
-                import_id: None
+                import_ids: smallvec![]
             }, true);
         });
     }
@@ -799,7 +802,7 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
             this.push_candidate(Candidate {
                 xform_self_ty, xform_ret_ty, item,
                 kind: WhereClauseCandidate(poly_trait_ref),
-                import_id: None
+                import_ids: smallvec![]
             }, true);
         });
     }
@@ -838,9 +841,10 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
             for trait_candidate in applicable_traits.iter() {
                 let trait_did = trait_candidate.def_id;
                 if duplicates.insert(trait_did) {
-                    let import_id = trait_candidate.import_id.map(|node_id|
-                        self.fcx.tcx.hir().node_to_hir_id(node_id));
-                    let result = self.assemble_extension_candidates_for_trait(import_id, trait_did);
+                    let import_ids = trait_candidate.import_ids.iter().map(|node_id|
+                        self.fcx.tcx.hir().node_to_hir_id(*node_id)).collect();
+                    let result = self.assemble_extension_candidates_for_trait(import_ids,
+                                                                              trait_did);
                     result?;
                 }
             }
@@ -852,7 +856,7 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
         let mut duplicates = FxHashSet::default();
         for trait_info in suggest::all_traits(self.tcx) {
             if duplicates.insert(trait_info.def_id) {
-                self.assemble_extension_candidates_for_trait(None, trait_info.def_id)?;
+                self.assemble_extension_candidates_for_trait(smallvec![], trait_info.def_id)?;
             }
         }
         Ok(())
@@ -890,7 +894,7 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
     }
 
     fn assemble_extension_candidates_for_trait(&mut self,
-                                               import_id: Option<hir::HirId>,
+                                               import_ids: SmallHirIdVec,
                                                trait_def_id: DefId)
                                                -> Result<(), MethodError<'tcx>> {
         debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})",
@@ -907,7 +911,7 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
                 let (xform_self_ty, xform_ret_ty) =
                     this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
                 this.push_candidate(Candidate {
-                    xform_self_ty, xform_ret_ty, item, import_id,
+                    xform_self_ty, xform_ret_ty, item, import_ids: import_ids.clone(),
                     kind: TraitCandidate(new_trait_ref),
                 }, true);
             });
@@ -924,7 +928,7 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
                 let (xform_self_ty, xform_ret_ty) =
                     self.xform_self_ty(&item, trait_ref.self_ty(), trait_substs);
                 self.push_candidate(Candidate {
-                    xform_self_ty, xform_ret_ty, item, import_id,
+                    xform_self_ty, xform_ret_ty, item, import_ids: import_ids.clone(),
                     kind: TraitCandidate(trait_ref),
                 }, false);
             }
@@ -1413,7 +1417,7 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
         Some(Pick {
             item: probes[0].0.item.clone(),
             kind: TraitPick,
-            import_id: probes[0].0.import_id,
+            import_ids: probes[0].0.import_ids.clone(),
             autoderefs: 0,
             autoref: None,
             unsize: None,
@@ -1652,7 +1656,7 @@ impl<'tcx> Candidate<'tcx> {
                     WhereClausePick(trait_ref.clone())
                 }
             },
-            import_id: self.import_id,
+            import_ids: self.import_ids.clone(),
             autoderefs: 0,
             autoref: None,
             unsize: None,
diff --git a/src/test/ui/lint/unused_import_warning_issue_45268.rs b/src/test/ui/lint/unused_import_warning_issue_45268.rs
new file mode 100644
index 0000000000000..9f3f5573a15d1
--- /dev/null
+++ b/src/test/ui/lint/unused_import_warning_issue_45268.rs
@@ -0,0 +1,49 @@
+// compile-pass
+
+#![warn(unused_imports)] // Warning explanation here, it's OK
+
+mod test {
+    pub trait A {
+        fn a();
+    }
+
+    impl A for () {
+        fn a() { }
+    }
+
+    pub trait B {
+        fn b(self);
+    }
+
+    impl B for () {
+        fn b(self) { }
+    }
+
+    pub trait Unused {
+    }
+}
+
+use test::Unused;   // This is really unused, so warning is OK
+use test::A;        // This is used by the test2::func() through import of super::*
+use test::B;        // This is used by the test2::func() through import of super::*
+
+mod test2 {
+    use super::*;
+    pub fn func() {
+        let _ = <()>::a();
+        let _ = ().b();
+        test3::inner_func();
+    }
+    mod test3 {
+    use super::*;
+    pub fn inner_func() {
+        let _ = <()>::a();
+        let _ = ().b();
+    }
+}
+
+}
+
+fn main() {
+    test2::func();
+}
diff --git a/src/test/ui/lint/unused_import_warning_issue_45268.stderr b/src/test/ui/lint/unused_import_warning_issue_45268.stderr
new file mode 100644
index 0000000000000..7392e99f7aef3
--- /dev/null
+++ b/src/test/ui/lint/unused_import_warning_issue_45268.stderr
@@ -0,0 +1,12 @@
+warning: unused import: `test::Unused`
+  --> $DIR/unused_import_warning_issue_45268.rs:26:5
+   |
+LL | use test::Unused;   // This is really unused, so warning is OK
+   |     ^^^^^^^^^^^^
+   |
+note: lint level defined here
+  --> $DIR/unused_import_warning_issue_45268.rs:3:9
+   |
+LL | #![warn(unused_imports)] // Warning explanation here, it's OK
+   |         ^^^^^^^^^^^^^^
+

From 5d2be7d1fa6e420b4265dfc27a622405bd4fc5b1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jesper=20Steen=20M=C3=B8ller?= <jesper@selskabet.org>
Date: Wed, 1 May 2019 15:17:43 +0200
Subject: [PATCH 02/10] Fix misleading indentation

---
 src/test/ui/lint/unused_import_warning_issue_45268.rs | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/src/test/ui/lint/unused_import_warning_issue_45268.rs b/src/test/ui/lint/unused_import_warning_issue_45268.rs
index 9f3f5573a15d1..0bd7751113593 100644
--- a/src/test/ui/lint/unused_import_warning_issue_45268.rs
+++ b/src/test/ui/lint/unused_import_warning_issue_45268.rs
@@ -35,15 +35,14 @@ mod test2 {
         test3::inner_func();
     }
     mod test3 {
-    use super::*;
-    pub fn inner_func() {
-        let _ = <()>::a();
-        let _ = ().b();
+        use super::*;
+        pub fn inner_func() {
+            let _ = <()>::a();
+            let _ = ().b();
+        }
     }
 }
 
-}
-
 fn main() {
     test2::func();
 }

From a300cab526497909ebb3bb0f744bcf3279dd2762 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jesper=20Steen=20M=C3=B8ller?= <jesper@selskabet.org>
Date: Thu, 2 May 2019 08:27:57 +0200
Subject: [PATCH 03/10] Revert the introduced typedefs

---
 src/librustc/hir/mod.rs                   | 5 +----
 src/librustc_resolve/lib.rs               | 8 ++++----
 src/librustc_typeck/check/method/probe.rs | 9 ++++-----
 3 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/src/librustc/hir/mod.rs b/src/librustc/hir/mod.rs
index 8ef5b24a9f279..9ce300ce0484a 100644
--- a/src/librustc/hir/mod.rs
+++ b/src/librustc/hir/mod.rs
@@ -2506,16 +2506,13 @@ pub type FreevarMap = NodeMap<Vec<Freevar<ast::NodeId>>>;
 
 pub type CaptureModeMap = NodeMap<CaptureClause>;
 
-pub type SmallHirIdVec = SmallVec<[HirId;1]>;
-pub type SmallNodeIdVec = SmallVec<[NodeId;1]>;
-
  // The TraitCandidate's import_ids is empty if the trait is defined in the same module, and
  // has length > 0 if the trait is found through an chain of imports, starting with the
  // import/use statement in the scope where the trait is used.
 #[derive(Clone, Debug)]
 pub struct TraitCandidate {
     pub def_id: DefId,
-    pub import_ids: SmallNodeIdVec,
+    pub import_ids: SmallVec<[NodeId; 1]>,
 }
 
 // Trait method resolution
diff --git a/src/librustc_resolve/lib.rs b/src/librustc_resolve/lib.rs
index 71721504d5add..635185fe2258a 100644
--- a/src/librustc_resolve/lib.rs
+++ b/src/librustc_resolve/lib.rs
@@ -29,7 +29,7 @@ use rustc::hir::def::{
 };
 use rustc::hir::def::Namespace::*;
 use rustc::hir::def_id::{CRATE_DEF_INDEX, LOCAL_CRATE, DefId};
-use rustc::hir::{Freevar, FreevarMap, TraitCandidate, TraitMap, GlobMap, SmallNodeIdVec};
+use rustc::hir::{Freevar, FreevarMap, TraitCandidate, TraitMap, GlobMap};
 use rustc::ty::{self, DefIdTree};
 use rustc::util::nodemap::{NodeMap, NodeSet, FxHashMap, FxHashSet, DefIdMap};
 use rustc::{bug, span_bug};
@@ -67,6 +67,7 @@ use std::collections::BTreeSet;
 use std::mem::replace;
 use rustc_data_structures::ptr_key::PtrKey;
 use rustc_data_structures::sync::Lrc;
+use smallvec::SmallVec;
 
 use diagnostics::{find_span_of_binding_until_next_binding, extend_span_to_previous_binding};
 use resolve_imports::{ImportDirective, ImportDirectiveSubclass, NameResolution, ImportResolver};
@@ -4658,10 +4659,9 @@ impl<'a> Resolver<'a> {
         }
     }
 
-    fn find_transitive_imports(&mut self, kind: &NameBindingKind<'_>,
-                               trait_name: &Ident) -> SmallNodeIdVec {
+    fn find_transitive_imports(&mut self, mut kind: &NameBindingKind<'_>,
+                               trait_name: &Ident) -> SmallVec<[NodeId; 1]> {
         let mut import_ids = smallvec![];
-        let mut kind = kind;
         while let NameBindingKind::Import { directive, binding, .. } = *kind {
             self.maybe_unused_trait_imports.insert(directive.id);
             self.add_to_glob_map(&directive, *trait_name);
diff --git a/src/librustc_typeck/check/method/probe.rs b/src/librustc_typeck/check/method/probe.rs
index 148b7d5edb570..314f7e97cd28d 100644
--- a/src/librustc_typeck/check/method/probe.rs
+++ b/src/librustc_typeck/check/method/probe.rs
@@ -7,7 +7,6 @@ use crate::check::autoderef::{self, Autoderef};
 use crate::check::FnCtxt;
 use crate::hir::def_id::DefId;
 use crate::hir::def::DefKind;
-use crate::hir::SmallHirIdVec;
 use crate::namespace::Namespace;
 
 use rustc_data_structures::sync::Lrc;
@@ -36,7 +35,7 @@ use std::mem;
 use std::ops::Deref;
 use std::cmp::max;
 
-use smallvec::smallvec;
+use smallvec::{smallvec, SmallVec};
 
 use self::CandidateKind::*;
 pub use self::PickKind::*;
@@ -124,7 +123,7 @@ struct Candidate<'tcx> {
     xform_ret_ty: Option<Ty<'tcx>>,
     item: ty::AssociatedItem,
     kind: CandidateKind<'tcx>,
-    import_ids: SmallHirIdVec,
+    import_ids: SmallVec<[hir::HirId; 1]>,
 }
 
 #[derive(Debug)]
@@ -149,7 +148,7 @@ enum ProbeResult {
 pub struct Pick<'tcx> {
     pub item: ty::AssociatedItem,
     pub kind: PickKind<'tcx>,
-    pub import_ids: hir::SmallHirIdVec,
+    pub import_ids: SmallVec<[hir::HirId; 1]>,
 
     // Indicates that the source expression should be autoderef'd N times
     //
@@ -894,7 +893,7 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
     }
 
     fn assemble_extension_candidates_for_trait(&mut self,
-                                               import_ids: SmallHirIdVec,
+                                               import_ids: SmallVec<[hir::HirId; 1]>,
                                                trait_def_id: DefId)
                                                -> Result<(), MethodError<'tcx>> {
         debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})",

From 719890502e47e09c86f7543e9efed55ed449af49 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jesper=20Steen=20M=C3=B8ller?= <jesper@selskabet.org>
Date: Thu, 2 May 2019 08:30:16 +0200
Subject: [PATCH 04/10] Improved name: first_import_id

---
 src/librustc/ich/impls_hir.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/librustc/ich/impls_hir.rs b/src/librustc/ich/impls_hir.rs
index eb57f08003ced..0869893fbad31 100644
--- a/src/librustc/ich/impls_hir.rs
+++ b/src/librustc/ich/impls_hir.rs
@@ -414,10 +414,10 @@ impl<'a> ToStableHashKey<StableHashingContext<'a>> for hir::TraitCandidate {
             import_ids,
         } = self;
 
-        let import_ids = import_ids.first().map(|node_id| hcx.node_to_hir_id(*node_id))
+        let first_import_id = import_ids.first().map(|node_id| hcx.node_to_hir_id(*node_id))
                                            .map(|hir_id| (hcx.local_def_path_hash(hir_id.owner),
                                                           hir_id.local_id));
-        (hcx.def_path_hash(*def_id), import_ids)
+        (hcx.def_path_hash(*def_id), first_import_id)
     }
 }
 

From 42255d93efe160600dd02711b7b009ea240945b4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jesper=20Steen=20M=C3=B8ller?= <jesper@selskabet.org>
Date: Thu, 2 May 2019 08:31:15 +0200
Subject: [PATCH 05/10] Reuse 'kind' parameter.

---
 src/librustc_resolve/lib.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/librustc_resolve/lib.rs b/src/librustc_resolve/lib.rs
index 635185fe2258a..d351802266ebb 100644
--- a/src/librustc_resolve/lib.rs
+++ b/src/librustc_resolve/lib.rs
@@ -4662,7 +4662,7 @@ impl<'a> Resolver<'a> {
     fn find_transitive_imports(&mut self, mut kind: &NameBindingKind<'_>,
                                trait_name: &Ident) -> SmallVec<[NodeId; 1]> {
         let mut import_ids = smallvec![];
-        while let NameBindingKind::Import { directive, binding, .. } = *kind {
+        while let NameBindingKind::Import { directive, binding, .. } = kind {
             self.maybe_unused_trait_imports.insert(directive.id);
             self.add_to_glob_map(&directive, *trait_name);
             import_ids.push(directive.id);

From 7dbb5e3b49b00c6bf0ce7b0e11a32eee38aeb8a3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jesper=20Steen=20M=C3=B8ller?= <jesper@selskabet.org>
Date: Thu, 2 May 2019 11:56:45 +0200
Subject: [PATCH 06/10] Use binding autoref, because we can.

---
 src/librustc/ich/impls_hir.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/librustc/ich/impls_hir.rs b/src/librustc/ich/impls_hir.rs
index 0869893fbad31..5bd359ba1f6aa 100644
--- a/src/librustc/ich/impls_hir.rs
+++ b/src/librustc/ich/impls_hir.rs
@@ -391,10 +391,10 @@ impl<'a> HashStable<StableHashingContext<'a>> for hir::TraitCandidate {
                                           hcx: &mut StableHashingContext<'a>,
                                           hasher: &mut StableHasher<W>) {
         hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
-            let &hir::TraitCandidate {
+            let hir::TraitCandidate {
                 def_id,
                 import_ids,
-            } = &self;
+            } = self;
 
             def_id.hash_stable(hcx, hasher);
             // We only use the outermost import NodeId as key

From fc34d5f608e3476bc7c5c4127d4e1ad1ab4fd01a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jesper=20Steen=20M=C3=B8ller?= <jesper@selskabet.org>
Date: Thu, 2 May 2019 13:40:12 +0200
Subject: [PATCH 07/10] Removed unneccesary reference for trait name

---
 src/librustc_resolve/lib.rs | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/librustc_resolve/lib.rs b/src/librustc_resolve/lib.rs
index d351802266ebb..c439ad9c315ee 100644
--- a/src/librustc_resolve/lib.rs
+++ b/src/librustc_resolve/lib.rs
@@ -4643,14 +4643,14 @@ impl<'a> Resolver<'a> {
                     false,
                     module.span,
                 ).is_ok() {
-                    let import_ids = self.find_transitive_imports(&binding.kind, &trait_name);
+                    let import_ids = self.find_transitive_imports(&binding.kind, trait_name);
                     let trait_def_id = module.def_id().unwrap();
                     found_traits.push(TraitCandidate { def_id: trait_def_id, import_ids });
                 }
             } else if let Res::Def(DefKind::TraitAlias, _) = binding.res() {
                 // For now, just treat all trait aliases as possible candidates, since we don't
                 // know if the ident is somewhere in the transitive bounds.
-                let import_ids = self.find_transitive_imports(&binding.kind, &trait_name);
+                let import_ids = self.find_transitive_imports(&binding.kind, trait_name);
                 let trait_def_id = binding.res().def_id();
                 found_traits.push(TraitCandidate { def_id: trait_def_id, import_ids });
             } else {
@@ -4660,11 +4660,11 @@ impl<'a> Resolver<'a> {
     }
 
     fn find_transitive_imports(&mut self, mut kind: &NameBindingKind<'_>,
-                               trait_name: &Ident) -> SmallVec<[NodeId; 1]> {
+                               trait_name: Ident) -> SmallVec<[NodeId; 1]> {
         let mut import_ids = smallvec![];
         while let NameBindingKind::Import { directive, binding, .. } = kind {
             self.maybe_unused_trait_imports.insert(directive.id);
-            self.add_to_glob_map(&directive, *trait_name);
+            self.add_to_glob_map(&directive, trait_name);
             import_ids.push(directive.id);
             kind = &binding.kind;
         };

From 6802082039285bc07736f8c9900a0410b5c1e7dc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jesper=20Steen=20M=C3=B8ller?= <jesper@selskabet.org>
Date: Thu, 2 May 2019 15:08:03 +0200
Subject: [PATCH 08/10] Hash all of the import_ids for the TraitCandidate.

---
 src/librustc/ich/impls_hir.rs                 | 12 ++++++------
 src/librustc_data_structures/stable_hasher.rs | 12 ++++++++++++
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/src/librustc/ich/impls_hir.rs b/src/librustc/ich/impls_hir.rs
index 5bd359ba1f6aa..5b2a1e783c039 100644
--- a/src/librustc/ich/impls_hir.rs
+++ b/src/librustc/ich/impls_hir.rs
@@ -7,6 +7,7 @@ use crate::hir::def_id::{DefId, LocalDefId, CrateNum, CRATE_DEF_INDEX};
 use crate::ich::{StableHashingContext, NodeIdHashingMode, Fingerprint};
 use rustc_data_structures::stable_hasher::{HashStable, ToStableHashKey,
                                            StableHasher, StableHasherResult};
+use smallvec::SmallVec;
 use std::mem;
 use syntax::ast;
 use syntax::attr;
@@ -397,14 +398,13 @@ impl<'a> HashStable<StableHashingContext<'a>> for hir::TraitCandidate {
             } = self;
 
             def_id.hash_stable(hcx, hasher);
-            // We only use the outermost import NodeId as key
-            import_ids.first().hash_stable(hcx, hasher);
+            import_ids.hash_stable(hcx, hasher);
         });
     }
 }
 
 impl<'a> ToStableHashKey<StableHashingContext<'a>> for hir::TraitCandidate {
-    type KeyType = (DefPathHash, Option<(DefPathHash, hir::ItemLocalId)>);
+    type KeyType = (DefPathHash, SmallVec<[(DefPathHash, hir::ItemLocalId); 1]>);
 
     fn to_stable_hash_key(&self,
                           hcx: &StableHashingContext<'a>)
@@ -414,10 +414,10 @@ impl<'a> ToStableHashKey<StableHashingContext<'a>> for hir::TraitCandidate {
             import_ids,
         } = self;
 
-        let first_import_id = import_ids.first().map(|node_id| hcx.node_to_hir_id(*node_id))
+        let import_keys = import_ids.iter().map(|node_id| hcx.node_to_hir_id(*node_id))
                                            .map(|hir_id| (hcx.local_def_path_hash(hir_id.owner),
-                                                          hir_id.local_id));
-        (hcx.def_path_hash(*def_id), first_import_id)
+                                                          hir_id.local_id)).collect();
+        (hcx.def_path_hash(*def_id), import_keys)
     }
 }
 
diff --git a/src/librustc_data_structures/stable_hasher.rs b/src/librustc_data_structures/stable_hasher.rs
index 19343a9250df3..c777f1fa82949 100644
--- a/src/librustc_data_structures/stable_hasher.rs
+++ b/src/librustc_data_structures/stable_hasher.rs
@@ -1,6 +1,7 @@
 use std::hash::{Hash, Hasher, BuildHasher};
 use std::marker::PhantomData;
 use std::mem;
+use smallvec::SmallVec;
 use crate::sip128::SipHasher128;
 use crate::indexed_vec;
 use crate::bit_set;
@@ -318,6 +319,17 @@ impl<T: HashStable<CTX>, CTX> HashStable<CTX> for Vec<T> {
     }
 }
 
+impl<A, CTX> HashStable<CTX> for SmallVec<[A; 1]> where A: HashStable<CTX> {
+    #[inline]
+    fn hash_stable<W: StableHasherResult>(&self,
+                                          ctx: &mut CTX,
+                                          hasher: &mut StableHasher<W>) {
+        for item in self {
+            item.hash_stable(ctx, hasher);
+        }
+    }
+}
+
 impl<T: ?Sized + HashStable<CTX>, CTX> HashStable<CTX> for Box<T> {
     #[inline]
     fn hash_stable<W: StableHasherResult>(&self,

From 6da7649f61fae784e1df991be5c688026ade3c84 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jesper=20Steen=20M=C3=B8ller?= <jesper@selskabet.org>
Date: Thu, 2 May 2019 20:16:48 +0200
Subject: [PATCH 09/10] Delegate SmallVec's stable_hash to array's stable_hash.

---
 src/librustc_data_structures/stable_hasher.rs | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/src/librustc_data_structures/stable_hasher.rs b/src/librustc_data_structures/stable_hasher.rs
index c777f1fa82949..fa573907d4c73 100644
--- a/src/librustc_data_structures/stable_hasher.rs
+++ b/src/librustc_data_structures/stable_hasher.rs
@@ -324,9 +324,7 @@ impl<A, CTX> HashStable<CTX> for SmallVec<[A; 1]> where A: HashStable<CTX> {
     fn hash_stable<W: StableHasherResult>(&self,
                                           ctx: &mut CTX,
                                           hasher: &mut StableHasher<W>) {
-        for item in self {
-            item.hash_stable(ctx, hasher);
-        }
+        (&self[..]).hash_stable(ctx, hasher);
     }
 }
 

From f5b5ca8b2351791fd3c29223d3e663760b5065ae Mon Sep 17 00:00:00 2001
From: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>
Date: Sun, 5 May 2019 00:12:38 +0300
Subject: [PATCH 10/10] Revert Cargo.lock changes accidentally introduced
 during rebase

---
 Cargo.lock | 15 +--------------
 1 file changed, 1 insertion(+), 14 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index f8dd4c91773be..ffa33393c3025 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -296,18 +296,6 @@ dependencies = [
  "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
-[[package]]
-name = "cargo_metadata"
-version = "0.6.4"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-dependencies = [
- "error-chain 0.12.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "semver 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.82 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde_derive 1.0.81 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde_json 1.0.33 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
 [[package]]
 name = "cargo_metadata"
 version = "0.7.1"
@@ -1624,7 +1612,7 @@ name = "miri"
 version = "0.1.0"
 dependencies = [
  "byteorder 1.2.7 (registry+https://github.com/rust-lang/crates.io-index)",
- "cargo_metadata 0.6.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cargo_metadata 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "colored 1.6.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "compiletest_rs 0.3.22 (registry+https://github.com/rust-lang/crates.io-index)",
  "directories 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -4079,7 +4067,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum byteorder 1.2.7 (registry+https://github.com/rust-lang/crates.io-index)" = "94f88df23a25417badc922ab0f5716cc1330e87f71ddd9203b3a3ccd9cedf75d"
 "checksum bytes 0.4.11 (registry+https://github.com/rust-lang/crates.io-index)" = "40ade3d27603c2cb345eb0912aec461a6dec7e06a4ae48589904e808335c7afa"
 "checksum bytesize 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "716960a18f978640f25101b5cbf1c6f6b0d3192fab36a2d98ca96f0ecbe41010"
-"checksum cargo_metadata 0.6.4 (registry+https://github.com/rust-lang/crates.io-index)" = "e5d1b4d380e1bab994591a24c2bdd1b054f64b60bef483a8c598c7c345bc3bbe"
 "checksum cargo_metadata 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)" = "585784cac9b05c93a53b17a0b24a5cdd1dfdda5256f030e089b549d2390cc720"
 "checksum cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)" = "5e5f3fee5eeb60324c2781f1e41286bdee933850fff9b3c672587fed5ec58c83"
 "checksum cfg-if 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)" = "082bb9b28e00d3c9d39cc03e64ce4cea0f1bb9b3fde493f0cbc008472d22bdf4"