Fix non-linux compilation

crates/ra_prof/Cargo.toml

@@ -15,6 +15,8 @@ once_cell = "1.3.1"
 backtrace = { version = "0.3.44", optional = true }
 cfg-if = "0.1.10"
 libc = "0.2.73"
+
+[target.'cfg(target_os = "linux")'.dependencies]
 perf-event = "0.4"
 
 [features]

crates/ra_prof/src/stop_watch.rs

@@ -1,11 +1,13 @@
-use crate::MemoryUsage;
 use std::{
     fmt,
     time::{Duration, Instant},
 };
 
+use crate::MemoryUsage;
+
 pub struct StopWatch {
     time: Instant,
+    #[cfg(target_os = "linux")]
     counter: Option<perf_event::Counter>,
     memory: Option<MemoryUsage>,
 }
@@ -18,12 +20,21 @@ pub struct StopWatchSpan {
 
 impl StopWatch {
     pub fn start() -> StopWatch {
-        let mut counter = perf_event::Builder::new().build().ok();
-        if let Some(counter) = &mut counter {
-            let _ = counter.enable();
-        }
+        #[cfg(target_os = "linux")]
+        let counter = {
+            let mut counter = perf_event::Builder::new().build().ok();
+            if let Some(counter) = &mut counter {
+                let _ = counter.enable();
+            }
+            counter
+        };
         let time = Instant::now();
-        StopWatch { time, counter, memory: None }
+        StopWatch {
+            time,
+            #[cfg(target_os = "linux")]
+            counter,
+            memory: None,
+        }
     }
     pub fn memory(mut self, yes: bool) -> StopWatch {
         if yes {
@@ -33,7 +44,12 @@ impl StopWatch {
     }
     pub fn elapsed(&mut self) -> StopWatchSpan {
         let time = self.time.elapsed();
+
+        #[cfg(target_os = "linux")]
         let instructions = self.counter.as_mut().and_then(|it| it.read().ok());
+        #[cfg(not(target_os = "linux"))]
+        let instructions = None;
+
         let memory = self.memory.map(|it| MemoryUsage::current() - it);
         StopWatchSpan { time, instructions, memory }
     }
@@ -65,6 +81,7 @@ impl fmt::Display for StopWatchSpan {
 // https://github.com/jimblandy/perf-event/issues/8
 impl Drop for StopWatch {
     fn drop(&mut self) {
+        #[cfg(target_os = "linux")]
         if let Some(mut counter) = self.counter.take() {
             let _ = counter.disable();
         }