change non-canonical clone impl to {*self}, fix some doc comments

compiler/rustc_pattern_analysis/src/lib.rs

@@ -141,7 +141,7 @@ pub struct MatchArm<'p, Cx: PatCx> {
 
 impl<'p, Cx: PatCx> Clone for MatchArm<'p, Cx> {
     fn clone(&self) -> Self {
-        Self { pat: self.pat, has_guard: self.has_guard, arm_data: self.arm_data }
+        *self
     }
 }
 

compiler/rustc_pattern_analysis/src/pat.rs

@@ -174,10 +174,7 @@ pub(crate) enum PatOrWild<'p, Cx: PatCx> {
 
 impl<'p, Cx: PatCx> Clone for PatOrWild<'p, Cx> {
     fn clone(&self) -> Self {
-        match self {
-            PatOrWild::Wild => PatOrWild::Wild,
-            PatOrWild::Pat(pat) => PatOrWild::Pat(pat),
-        }
+        *self
     }
 }
 

compiler/rustc_pattern_analysis/src/usefulness.rs

@@ -824,7 +824,7 @@ struct PlaceCtxt<'a, Cx: PatCx> {
 impl<'a, Cx: PatCx> Copy for PlaceCtxt<'a, Cx> {}
 impl<'a, Cx: PatCx> Clone for PlaceCtxt<'a, Cx> {
     fn clone(&self) -> Self {
-        Self { cx: self.cx, ty: self.ty }
+        *self
     }
 }