inbound: Add a box layer to reduce compile times (#1317)

The inbound proxy builds in 30-40 minutes on recent nightlies. This can
be reduced to 3-4 minutes with a boxing layer. This change adds such a
layer so that fuzzing builds can complete in a timely fashion.

(cherry picked from commit 66f2f03)
Signed-off-by: Oliver Gould <ver@buoyant.io>

linkerd/app/inbound/fuzz/Cargo.toml

@@ -18,6 +18,7 @@ http = "0.2"
 linkerd-app-core = { path = "../../core" }
 linkerd-app-inbound = { path = ".." }
 linkerd-app-test = { path = "../../test" }
+linkerd-proxy-identity = { path = "../../../proxy/identity", features = ["test-util"] }
 linkerd-tracing = { path = "../../../tracing", features = ["ansi"] }
 tracing = "0.1"
 

linkerd/app/inbound/src/http/router.rs

@@ -116,7 +116,13 @@ impl<C> Inbound<C> {
                     rt.span_sink.clone(),
                     super::trace_labels(),
                 ))
-                .push_on_service(http::BoxResponse::layer());
+                .push_on_service(svc::layers()
+                    .push(http::BoxResponse::layer())
+                    // This box is needed to reduce compile times on recent (2021-10-17) nightlies,
+                    // though this may be fixed by https://github.com/rust-lang/rust/pull/89831. It
+                    // should be removed when possible.
+                    .push(svc::BoxService::layer())
+                );
 
             // Attempts to discover a service profile for each logical target (as
             // informed by the request's headers). The stack is cached until a