Cleanup: rewrite conditional as match

As suggested by @Centril.

Signed-off-by: Philipp Gesang <phg@phi-gamma.net>

Author: phi-gamma

src/librustc/traits/error_reporting/on_unimplemented.rs

@@ -59,49 +59,45 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     fn describe_enclosure(&self, hir_id: hir::HirId) -> Option<&'static str> {
         let hir = &self.tcx.hir();
         let node = hir.find(hir_id)?;
-        if let hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, _, body_id), .. }) = &node {
-            self.describe_generator(*body_id).or_else(|| {
-                Some(if let hir::FnHeader { asyncness: hir::IsAsync::Async, .. } = sig.header {
-                    "an async function"
-                } else {
-                    "a function"
+        match &node {
+            hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(sig, _, body_id), .. }) => {
+                self.describe_generator(*body_id).or_else(|| {
+                    Some(if let hir::FnHeader { asyncness: hir::IsAsync::Async, .. } = sig.header {
+                        "an async function"
+                    } else {
+                        "a function"
+                    })
                 })
-            })
-        } else if let hir::Node::TraitItem(hir::TraitItem {
-            kind: hir::TraitItemKind::Method(_, hir::TraitMethod::Provided(body_id)),
-            ..
-        }) = &node
-        {
-            self.describe_generator(*body_id).or_else(|| Some("a trait method"))
-        } else if let hir::Node::ImplItem(hir::ImplItem {
-            kind: hir::ImplItemKind::Method(sig, body_id),
-            ..
-        }) = &node
-        {
-            self.describe_generator(*body_id).or_else(|| {
+            }
+            hir::Node::TraitItem(hir::TraitItem {
+                kind: hir::TraitItemKind::Method(_, hir::TraitMethod::Provided(body_id)),
+                ..
+            }) => self.describe_generator(*body_id).or_else(|| Some("a trait method")),
+            hir::Node::ImplItem(hir::ImplItem {
+                kind: hir::ImplItemKind::Method(sig, body_id),
+                ..
+            }) => self.describe_generator(*body_id).or_else(|| {
                 Some(if let hir::FnHeader { asyncness: hir::IsAsync::Async, .. } = sig.header {
                     "an async method"
                 } else {
                     "a method"
                 })
-            })
-        } else if let hir::Node::Expr(hir::Expr {
-            kind: hir::ExprKind::Closure(_is_move, _, body_id, _, gen_movability),
-            ..
-        }) = &node
-        {
-            self.describe_generator(*body_id).or_else(|| {
+            }),
+            hir::Node::Expr(hir::Expr {
+                kind: hir::ExprKind::Closure(_is_move, _, body_id, _, gen_movability),
+                ..
+            }) => self.describe_generator(*body_id).or_else(|| {
                 Some(if gen_movability.is_some() { "an async closure" } else { "a closure" })
-            })
-        } else if let hir::Node::Expr(hir::Expr { .. }) = &node {
-            let parent_hid = hir.get_parent_node(hir_id);
-            if parent_hid != hir_id {
-                return self.describe_enclosure(parent_hid);
-            } else {
-                None
+            }),
+            hir::Node::Expr(hir::Expr { .. }) => {
+                let parent_hid = hir.get_parent_node(hir_id);
+                if parent_hid != hir_id {
+                    return self.describe_enclosure(parent_hid);
+                } else {
+                    None
+                }
             }
-        } else {
-            None
+            _ => None,
         }
     }