Upgrade to Rust stable 1.47.0. (#10933)

The changelog is here:
https://blog.rust-lang.org/2020/10/08/Rust-1.47.html

The most relevant change is shorter backtraces by default:
https://blog.rust-lang.org/2020/10/08/Rust-1.47.html#shorter-backtraces

rust-toolchain

@@ -1 +1 @@
-1.46.0
+1.47.0

src/rust/engine/fs/src/lib.rs

@@ -305,10 +305,7 @@ impl GitignoreStyleExcludes {
   }
 
   fn is_ignored(&self, stat: &Stat) -> bool {
-    let is_dir = match stat {
-      &Stat::Dir(_) => true,
-      _ => false,
-    };
+    let is_dir = matches!(stat, &Stat::Dir(_));
     self.is_ignored_path(stat.path(), is_dir)
   }
 
@@ -357,17 +354,11 @@ impl StrictGlobMatching {
   }
 
   pub fn should_check_glob_matches(&self) -> bool {
-    match self {
-      &StrictGlobMatching::Ignore => false,
-      _ => true,
-    }
+    !matches!(self, &StrictGlobMatching::Ignore)
   }
 
   pub fn should_throw_on_error(&self) -> bool {
-    match self {
-      &StrictGlobMatching::Error(_) => true,
-      _ => false,
-    }
+    matches!(self, &StrictGlobMatching::Error(_))
   }
 }
 

src/rust/engine/graph/src/lib.rs

@@ -686,13 +686,9 @@ impl<N: Node> Graph<N> {
   ) -> Result<Vec<Generation>, N::Error> {
     let generations = {
       let inner = self.inner.lock();
-      let dep_ids = inner
+      inner
         .pg
         .neighbors_directed(entry_id, Direction::Outgoing)
-        .collect::<Vec<_>>();
-
-      dep_ids
-        .into_iter()
         .map(|dep_id| {
           let mut entry = inner
             .entry_for_id(dep_id)

src/rust/engine/rule_graph/src/builder.rs

@@ -1015,11 +1015,13 @@ impl<R: Rule> Builder<R> {
               to_visit.extend(
                 edge_refs
                   .iter()
-                  .filter(|edge_ref| match graph[edge_ref.target()].deleted_reason() {
-                    Some(NodePrunedReason::Ambiguous)
-                    | Some(NodePrunedReason::NoSourceOfParam)
-                    | Some(NodePrunedReason::NoValidCombinationsOfDependencies) => true,
-                    _ => false,
+                  .filter(|edge_ref| {
+                    matches!(
+                      graph[edge_ref.target()].deleted_reason(),
+                      Some(NodePrunedReason::Ambiguous)
+                        | Some(NodePrunedReason::NoSourceOfParam)
+                        | Some(NodePrunedReason::NoValidCombinationsOfDependencies)
+                    )
                   })
                   .map(|edge_ref| edge_ref.target()),
               );