Run benchmarks once, as a test by default.

E.g. if `foo.rs` looks like

    #![feature(test)]
    extern crate test;

    #[bench]
    fn bar(b: &mut test::Bencher) {
        b.iter(|| {
            1
        })
    }

    #[test]
    fn baz() {}

    #[bench]
    fn qux(b: &mut test::Bencher) {
        b.iter(|| {
            panic!()
        })
    }

Then

    $ rustc --test foo.rs
    $ ./foo

    running 3 tests
    test baz ... ok
    test qux ... FAILED
    test bar ... ok

    failures:

    ---- qux stdout ----
    	thread 'qux' panicked at 'explicit panic', bench.rs:17

    failures:
        qux

    test result: FAILED. 2 passed; 1 failed; 0 ignored; 0 measured

    $ ./foo --bench ba

    running 2 tests
    test baz ... ignored
    test bar ... bench:        97 ns/iter (+/- 74)

    test result: ok. 0 passed; 0 failed; 1 ignored; 1 measured

In particular, the two benchmark are being run as tests in the default
mode.

This helps for the main distribution, since benchmarks are only run with
`PLEASE_BENCH=1`, which is rarely set (and never set on the test bots),
and helps for code-coverage tools: benchmarks are run and so don't count
as dead code.

Fixes #15842.

src/compiletest/compiletest.rs

@@ -269,7 +269,7 @@ pub fn test_opts(config: &Config) -> test::TestOpts {
         run_ignored: config.run_ignored,
         logfile: config.logfile.clone(),
         run_tests: true,
-        run_benchmarks: true,
+        bench_benchmarks: true,
         nocapture: env::var("RUST_TEST_NOCAPTURE").is_ok(),
         color: test::AutoColor,
     }

src/libtest/lib.rs

@@ -139,7 +139,7 @@ impl TestDesc {
 }
 
 /// Represents a benchmark function.
-pub trait TDynBenchFn {
+pub trait TDynBenchFn: Send {
     fn run(&self, harness: &mut Bencher);
 }
 
@@ -285,7 +285,7 @@ pub struct TestOpts {
     pub filter: Option<String>,
     pub run_ignored: bool,
     pub run_tests: bool,
-    pub run_benchmarks: bool,
+    pub bench_benchmarks: bool,
     pub logfile: Option<PathBuf>,
     pub nocapture: bool,
     pub color: ColorConfig,
@@ -298,7 +298,7 @@ impl TestOpts {
             filter: None,
             run_ignored: false,
             run_tests: false,
-            run_benchmarks: false,
+            bench_benchmarks: false,
             logfile: None,
             nocapture: false,
             color: AutoColor,
@@ -377,8 +377,8 @@ pub fn parse_opts(args: &[String]) -> Option<OptRes> {
     let logfile = matches.opt_str("logfile");
     let logfile = logfile.map(|s| PathBuf::from(&s));
 
-    let run_benchmarks = matches.opt_present("bench");
+    let bench_benchmarks = matches.opt_present("bench");
-    let run_tests = ! run_benchmarks ||
+    let run_tests = ! bench_benchmarks ||
         matches.opt_present("test");
 
     let mut nocapture = matches.opt_present("nocapture");
@@ -400,7 +400,7 @@ pub fn parse_opts(args: &[String]) -> Option<OptRes> {
         filter: filter,
         run_ignored: run_ignored,
         run_tests: run_tests,
-        run_benchmarks: run_benchmarks,
+        bench_benchmarks: bench_benchmarks,
         logfile: logfile,
         nocapture: nocapture,
         color: color,
@@ -778,7 +778,11 @@ fn run_tests<F>(opts: &TestOpts,
                 mut callback: F) -> io::Result<()> where
     F: FnMut(TestEvent) -> io::Result<()>,
 {
-    let filtered_tests = filter_tests(opts, tests);
+    let mut filtered_tests = filter_tests(opts, tests);
+    if !opts.bench_benchmarks {
+        filtered_tests = convert_benchmarks_to_tests(filtered_tests);
+    }
+
     let filtered_descs = filtered_tests.iter()
                                        .map(|t| t.desc.clone())
                                        .collect();
@@ -824,14 +828,16 @@ fn run_tests<F>(opts: &TestOpts,
         pending -= 1;
     }
 
+    if opts.bench_benchmarks {
         // All benchmarks run at the end, in serial.
         // (this includes metric fns)
         for b in filtered_benchs_and_metrics {
             try!(callback(TeWait(b.desc.clone(), b.testfn.padding())));
-        run_test(opts, !opts.run_benchmarks, b, tx.clone());
+            run_test(opts, false, b, tx.clone());
             let (test, result, stdout) = rx.recv().unwrap();
             try!(callback(TeResult(test, result, stdout)));
         }
+    }
     Ok(())
 }
 
@@ -893,6 +899,22 @@ pub fn filter_tests(opts: &TestOpts, tests: Vec<TestDescAndFn>) -> Vec<TestDescA
     filtered
 }
 
+pub fn convert_benchmarks_to_tests(tests: Vec<TestDescAndFn>) -> Vec<TestDescAndFn> {
+    // convert benchmarks to tests, if we're not benchmarking them
+    tests.into_iter().map(|x| {
+        let testfn = match x.testfn {
+            DynBenchFn(bench) => {
+                DynTestFn(Box::new(move || bench::run_once(|b| bench.run(b))))
+            }
+            StaticBenchFn(benchfn) => {
+                DynTestFn(Box::new(move || bench::run_once(|b| benchfn(b))))
+            }
+            f => f
+        };
+        TestDescAndFn { desc: x.desc, testfn: testfn }
+    }).collect()
+}
+
 pub fn run_test(opts: &TestOpts,
                 force_ignore: bool,
                 test: TestDescAndFn,
@@ -1159,6 +1181,15 @@ pub mod bench {
             mb_s: mb_s as usize
         }
     }
+
+    pub fn run_once<F>(f: F) where F: FnOnce(&mut Bencher) {
+        let mut bs = Bencher {
+            iterations: 0,
+            dur: Duration::nanoseconds(0),
+            bytes: 0
+        };
+        bs.bench_n(1, f);
+    }
 }
 
 #[cfg(test)]