tree-wide: replace single-leaf match with if let

Fixes the clippy warning:

  you seem to be trying to use `match` for destructuring a single
  pattern. Consider using `if let`

https://rust-lang.github.io/rust-clippy/master/index.html#single_match

BUG=None
TEST=bin/clippy

Change-Id: I5901a1fa0f487e0f012bad4c21b43ea300348031
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2885786
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Daniel Verkamp <dverkamp@chromium.org>
Reviewed-by: Zach Reizner <zachr@chromium.org>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>

bin/clippy

@@ -39,7 +39,6 @@ SUPPRESS=(
     needless_range_loop
     option_map_unit_fn
     range_plus_one
-    single_match
     slow_vector_initialization
     unnecessary_filter_map
     unnecessary_mut_passed

rutabaga_gfx/src/cross_domain/cross_domain.rs

@@ -211,28 +211,22 @@ impl RutabagaContext for CrossDomainContext {
     }
 
     fn attach(&mut self, resource: &mut RutabagaResource) {
-        match resource.blob_mem {
-            RUTABAGA_BLOB_MEM_GUEST => {
-                self.context_resources.insert(
-                    resource.resource_id,
-                    CrossDomainResource {
-                        handle: None,
-                        backing_iovecs: resource.backing_iovecs.take(),
-                    },
-                );
-            }
-            _ => match resource.handle {
-                Some(ref handle) => {
-                    self.context_resources.insert(
-                        resource.resource_id,
-                        CrossDomainResource {
-                            handle: Some(handle.clone()),
-                            backing_iovecs: None,
-                        },
-                    );
-                }
-                _ => (),
-            },
+        if resource.blob_mem == RUTABAGA_BLOB_MEM_GUEST {
+            self.context_resources.insert(
+                resource.resource_id,
+                CrossDomainResource {
+                    handle: None,
+                    backing_iovecs: resource.backing_iovecs.take(),
+                },
+            );
+        } else if let Some(ref handle) = resource.handle {
+            self.context_resources.insert(
+                resource.resource_id,
+                CrossDomainResource {
+                    handle: Some(handle.clone()),
+                    backing_iovecs: None,
+                },
+            );
         }
     }
 
@@ -261,14 +255,11 @@ impl RutabagaComponent for CrossDomain {
 
     fn get_capset(&self, _capset_id: u32, _version: u32) -> Vec<u8> {
         let mut caps: CrossDomainCapabilities = Default::default();
-        match self.channels {
-            Some(ref channels) => {
-                for channel in channels {
-                    caps.supported_channels = 1 << channel.channel_type;
-                }
+        if let Some(ref channels) = self.channels {
+            for channel in channels {
+                caps.supported_channels = 1 << channel.channel_type;
             }
-            None => (),
-        };
+        }
 
         if self.gralloc.lock().supports_dmabuf() {
             caps.supports_dmabuf = 1;

src/gdb.rs

@@ -175,11 +175,12 @@ impl SingleThreadOps for GdbStub {
 
         // Polling
         loop {
-            match self
+            // TODO(keiichiw): handle error?
+            if let Ok(msg) = self
                 .from_vcpu
                 .recv_timeout(std::time::Duration::from_millis(100))
             {
-                Ok(msg) => match msg.msg {
+                match msg.msg {
                     VcpuDebugStatus::HitBreakPoint => {
                         if single_step {
                             return Ok(StopReason::DoneStep);
@@ -190,9 +191,8 @@ impl SingleThreadOps for GdbStub {
                     status => {
                         error!("Unexpected VcpuDebugStatus: {:?}", status);
                     }
-                },
-                Err(_) => {} // TODO(keiichiw): handle error?
-            };
+                }
+            }
 
             if check_gdb_interrupt() {
                 self.vm_request(VmRequest::Suspend).map_err(|e| {

vm_memory/src/guest_memory.rs

@@ -325,9 +325,8 @@ impl GuestMemory {
             for (_, region) in self.regions.iter().enumerate() {
                 let ret = region.mapping.use_hugepages();
 
-                match ret {
-                    Err(err) => println!("Failed to enable HUGEPAGE for mapping {}", err),
-                    Ok(_) => (),
+                if let Err(err) = ret {
+                    println!("Failed to enable HUGEPAGE for mapping {}", err);
                 }
             }
         }