Move some impls.

`HashStableContext` impls should be in `hcx.rs`, and `HashStable` impls
should be in `impls_syntax.rs`. This commit moves a few that are in the
wrong file.

Author: nnethercote

compiler/rustc_query_system/src/ich/hcx.rs

@@ -1,5 +1,4 @@
-use rustc_ast as ast;
-use rustc_data_structures::stable_hasher::{HashStable, HashingControls, StableHasher};
+use rustc_data_structures::stable_hasher::HashingControls;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::definitions::DefPathHash;
 use rustc_session::Session;
@@ -67,13 +66,6 @@ impl<'a> StableHashingContext<'a> {
     }
 }
 
-impl<'a> HashStable<StableHashingContext<'a>> for ast::NodeId {
-    #[inline]
-    fn hash_stable(&self, _: &mut StableHashingContext<'a>, _: &mut StableHasher) {
-        panic!("Node IDs should not appear in incremental state");
-    }
-}
-
 impl<'a> rustc_span::HashStableContext for StableHashingContext<'a> {
     #[inline]
     fn unstable_opts_incremental_ignore_spans(&self) -> bool {
@@ -108,4 +100,7 @@ impl<'a> rustc_span::HashStableContext for StableHashingContext<'a> {
     }
 }
 
+impl<'a> rustc_abi::HashStableContext for StableHashingContext<'a> {}
+impl<'a> rustc_ast::HashStableContext for StableHashingContext<'a> {}
+impl<'a> rustc_hir::HashStableContext for StableHashingContext<'a> {}
 impl<'a> rustc_session::HashStableContext for StableHashingContext<'a> {}

compiler/rustc_query_system/src/ich/impls_syntax.rs

@@ -2,14 +2,18 @@
 //! from various crates in no particular order.
 
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
-use rustc_hir::{self as hir, HashIgnoredAttrId};
 use rustc_span::{SourceFile, Symbol, sym};
 use smallvec::SmallVec;
+use {rustc_ast as ast, rustc_hir as hir};
 
 use crate::ich::StableHashingContext;
 
-impl<'ctx> rustc_abi::HashStableContext for StableHashingContext<'ctx> {}
-impl<'ctx> rustc_ast::HashStableContext for StableHashingContext<'ctx> {}
+impl<'a> HashStable<StableHashingContext<'a>> for ast::NodeId {
+    #[inline]
+    fn hash_stable(&self, _: &mut StableHashingContext<'a>, _: &mut StableHasher) {
+        panic!("Node IDs should not appear in incremental state");
+    }
+}
 
 impl<'a> HashStable<StableHashingContext<'a>> for [hir::Attribute] {
     fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
@@ -49,8 +53,6 @@ fn is_ignored_attr(name: Symbol) -> bool {
     IGNORED_ATTRIBUTES.contains(&name)
 }
 
-impl<'ctx> rustc_hir::HashStableContext for StableHashingContext<'ctx> {}
-
 impl<'a> HashStable<StableHashingContext<'a>> for SourceFile {
     fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
         let SourceFile {