Auto merge of #50466 - kennytm:rustbuild-stage0-lib-test, r=Mark-Simulacrum

rustbuild: Allow quick testing of libstd and libcore at stage0

This PR implemented two features:

1. Added a `--no-doc` flag to allow testing a crate *without* doc tests. In this mode, we don't need to build rustdoc, and thus we can skip building the stage2 compiler. (Ideally stage0 test should use the bootstrap rustdoc, but I don't want to mess up the core builder logic here)

2. Moved all libcore tests externally and added a tidy test to ensure we don't accidentally add `#[test]` into libcore.

After this PR, one could run `./x.py test --stage 0 --no-doc src/libstd` to test `libstd` without building the compiler, thus enables us to quickly test new library features.

src/bootstrap/README.md

@@ -64,6 +64,10 @@ The script accepts commands, flags, and arguments to determine what to do:
   # execute tests in the standard library in stage0
   ./x.py test --stage 0 src/libstd
 
+  # execute tests in the core and standard library in stage0,
+  # without running doc tests (thus avoid depending on building the compiler)
+  ./x.py test --stage 0 --no-doc src/libcore src/libstd
+
   # execute all doc tests
   ./x.py test src/doc
   ```

src/bootstrap/builder.rs

@@ -25,7 +25,7 @@ use compile;
 use install;
 use dist;
 use util::{exe, libdir, add_lib_path};
-use {Build, Mode};
+use {Build, Mode, DocTests};
 use cache::{INTERNER, Interned, Cache};
 use check;
 use test;
@@ -591,6 +591,8 @@ impl<'a> Builder<'a> {
                 format!("{} {}", env::var("RUSTFLAGS").unwrap_or_default(), extra_args));
         }
 
+        let want_rustdoc = self.doc_tests != DocTests::No;
+
         // Customize the compiler we're running. Specify the compiler to cargo
         // as our shim and then pass it some various options used to configure
         // how the actual compiler itself is called.
@@ -607,7 +609,7 @@ impl<'a> Builder<'a> {
              .env("RUSTC_LIBDIR", self.rustc_libdir(compiler))
              .env("RUSTC_RPATH", self.config.rust_rpath.to_string())
              .env("RUSTDOC", self.out.join("bootstrap/debug/rustdoc"))
-             .env("RUSTDOC_REAL", if cmd == "doc" || cmd == "test" {
+             .env("RUSTDOC_REAL", if cmd == "doc" || (cmd == "test" && want_rustdoc) {
                  self.rustdoc(compiler.host)
              } else {
                  PathBuf::from("/path/to/nowhere/rustdoc/not/required")
@@ -624,7 +626,7 @@ impl<'a> Builder<'a> {
         if let Some(ref error_format) = self.config.rustc_error_format {
             cargo.env("RUSTC_ERROR_FORMAT", error_format);
         }
-        if cmd != "build" && cmd != "check" {
+        if cmd != "build" && cmd != "check" && want_rustdoc {
             cargo.env("RUSTDOC_LIBDIR", self.rustc_libdir(self.compiler(2, self.config.build)));
         }
 
@@ -1407,4 +1409,39 @@ mod __test {
             },
         ]);
     }
+
+    #[test]
+    fn test_with_no_doc_stage0() {
+        let mut config = configure(&[], &[]);
+        config.stage = Some(0);
+        config.cmd = Subcommand::Test {
+            paths: vec!["src/libstd".into()],
+            test_args: vec![],
+            rustc_args: vec![],
+            fail_fast: true,
+            doc_tests: DocTests::No,
+        };
+
+        let build = Build::new(config);
+        let mut builder = Builder::new(&build);
+
+        let host = INTERNER.intern_str("A");
+
+        builder.run_step_descriptions(
+            &[StepDescription::from::<test::Crate>()],
+            &["src/libstd".into()],
+        );
+
+        // Ensure we don't build any compiler artifacts.
+        assert!(builder.cache.all::<compile::Rustc>().is_empty());
+        assert_eq!(first(builder.cache.all::<test::Crate>()), &[
+            test::Crate {
+                compiler: Compiler { host, stage: 0 },
+                target: host,
+                mode: Mode::Libstd,
+                test_kind: test::TestKind::Test,
+                krate: INTERNER.intern_str("std"),
+            },
+        ]);
+    }
 }

src/bootstrap/flags.rs

@@ -19,7 +19,7 @@ use std::process;
 
 use getopts::Options;
 
-use Build;
+use {Build, DocTests};
 use config::Config;
 use metadata;
 use builder::Builder;
@@ -62,7 +62,7 @@ pub enum Subcommand {
         test_args: Vec<String>,
         rustc_args: Vec<String>,
         fail_fast: bool,
-        doc_tests: bool,
+        doc_tests: DocTests,
     },
     Bench {
         paths: Vec<PathBuf>,
@@ -171,7 +171,8 @@ To learn more about a subcommand, run `./x.py <subcommand> -h`");
                     "extra options to pass the compiler when running tests",
                     "ARGS",
                 );
-                opts.optflag("", "doc", "run doc tests");
+                opts.optflag("", "no-doc", "do not run doc tests");
+                opts.optflag("", "doc", "only run doc tests");
             },
             "bench" => { opts.optmulti("", "test-args", "extra arguments", "ARGS"); },
             "clean" => { opts.optflag("", "all", "clean all build artifacts"); },
@@ -324,7 +325,13 @@ Arguments:
                     test_args: matches.opt_strs("test-args"),
                     rustc_args: matches.opt_strs("rustc-args"),
                     fail_fast: !matches.opt_present("no-fail-fast"),
-                    doc_tests: matches.opt_present("doc"),
+                    doc_tests: if matches.opt_present("doc") {
+                        DocTests::Only
+                    } else if matches.opt_present("no-doc") {
+                        DocTests::No
+                    } else {
+                        DocTests::Yes
+                    }
                 }
             }
             "bench" => {
@@ -411,10 +418,10 @@ impl Subcommand {
         }
     }
 
-    pub fn doc_tests(&self) -> bool {
+    pub fn doc_tests(&self) -> DocTests {
         match *self {
             Subcommand::Test { doc_tests, .. } => doc_tests,
-            _ => false,
+            _ => DocTests::Yes,
         }
     }
 }

src/bootstrap/lib.rs

@@ -210,6 +210,16 @@ pub struct Compiler {
     host: Interned<String>,
 }
 
+#[derive(PartialEq, Eq, Copy, Clone, Debug)]
+pub enum DocTests {
+    // Default, run normal tests and doc tests.
+    Yes,
+    // Do not run any doc tests.
+    No,
+    // Only run doc tests.
+    Only,
+}
+
 /// Global configuration for the build system.
 ///
 /// This structure transitively contains all configuration for the build system.
@@ -233,7 +243,7 @@ pub struct Build {
     rustfmt_info: channel::GitInfo,
     local_rebuild: bool,
     fail_fast: bool,
-    doc_tests: bool,
+    doc_tests: DocTests,
     verbosity: usize,
 
     // Targets for which to build.
@@ -294,7 +304,7 @@ impl Crate {
 ///
 /// These entries currently correspond to the various output directories of the
 /// build system, with each mod generating output in a different directory.
-#[derive(Debug, Hash, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Hash, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
 pub enum Mode {
     /// Build the standard library, placing output in the "stageN-std" directory.
     Libstd,

src/bootstrap/test.rs

@@ -32,13 +32,13 @@ use dist;
 use native;
 use tool::{self, Tool};
 use util::{self, dylib_path, dylib_path_var};
-use Mode;
+use {Mode, DocTests};
 use toolstate::ToolState;
 
 const ADB_TEST_DIR: &str = "/data/tmp/work";
 
 /// The two modes of the test runner; tests or benchmarks.
-#[derive(Debug, PartialEq, Eq, Hash, Copy, Clone)]
+#[derive(Debug, PartialEq, Eq, Hash, Copy, Clone, PartialOrd, Ord)]
 pub enum TestKind {
     /// Run `cargo test`
     Test,
@@ -1407,13 +1407,13 @@ impl Step for CrateNotDefault {
 }
 
 
-#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct Crate {
-    compiler: Compiler,
+    pub compiler: Compiler,
-    target: Interned<String>,
+    pub target: Interned<String>,
-    mode: Mode,
+    pub mode: Mode,
-    test_kind: TestKind,
+    pub test_kind: TestKind,
-    krate: Interned<String>,
+    pub krate: Interned<String>,
 }
 
 impl Step for Crate {
@@ -1519,9 +1519,15 @@ impl Step for Crate {
         if test_kind.subcommand() == "test" && !builder.fail_fast {
             cargo.arg("--no-fail-fast");
         }
-        if builder.doc_tests {
+        match builder.doc_tests {
+            DocTests::Only => {
                 cargo.arg("--doc");
             }
+            DocTests::No => {
+                cargo.args(&["--lib", "--bins", "--examples", "--tests", "--benches"]);
+            }
+            DocTests::Yes => {}
+        }
 
         cargo.arg("-p").arg(krate);
 

src/libcore/lib.rs

@@ -50,6 +50,15 @@
 
 // Since libcore defines many fundamental lang items, all tests live in a
 // separate crate, libcoretest, to avoid bizarre issues.
+//
+// Here we explicitly #[cfg]-out this whole crate when testing. If we don't do
+// this, both the generated test artifact and the linked libtest (which
+// transitively includes libcore) will both define the same set of lang items,
+// and this will cause the E0152 "duplicate lang item found" error. See
+// discussion in #50466 for details.
+//
+// This cfg won't affect doc tests.
+#![cfg(not(test))]
 
 #![stable(feature = "core", since = "1.6.0")]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",

src/libcore/slice/memchr.rs

@@ -135,85 +135,3 @@ pub fn memrchr(x: u8, text: &[u8]) -> Option<usize> {
     // find the byte before the point the body loop stopped
     text[..offset].iter().rposition(|elt| *elt == x)
 }
-
-// test fallback implementations on all platforms
-#[test]
-fn matches_one() {
-    assert_eq!(Some(0), memchr(b'a', b"a"));
-}
-
-#[test]
-fn matches_begin() {
-    assert_eq!(Some(0), memchr(b'a', b"aaaa"));
-}
-
-#[test]
-fn matches_end() {
-    assert_eq!(Some(4), memchr(b'z', b"aaaaz"));
-}
-
-#[test]
-fn matches_nul() {
-    assert_eq!(Some(4), memchr(b'\x00', b"aaaa\x00"));
-}
-
-#[test]
-fn matches_past_nul() {
-    assert_eq!(Some(5), memchr(b'z', b"aaaa\x00z"));
-}
-
-#[test]
-fn no_match_empty() {
-    assert_eq!(None, memchr(b'a', b""));
-}
-
-#[test]
-fn no_match() {
-    assert_eq!(None, memchr(b'a', b"xyz"));
-}
-
-#[test]
-fn matches_one_reversed() {
-    assert_eq!(Some(0), memrchr(b'a', b"a"));
-}
-
-#[test]
-fn matches_begin_reversed() {
-    assert_eq!(Some(3), memrchr(b'a', b"aaaa"));
-}
-
-#[test]
-fn matches_end_reversed() {
-    assert_eq!(Some(0), memrchr(b'z', b"zaaaa"));
-}
-
-#[test]
-fn matches_nul_reversed() {
-    assert_eq!(Some(4), memrchr(b'\x00', b"aaaa\x00"));
-}
-
-#[test]
-fn matches_past_nul_reversed() {
-    assert_eq!(Some(0), memrchr(b'z', b"z\x00aaaa"));
-}
-
-#[test]
-fn no_match_empty_reversed() {
-    assert_eq!(None, memrchr(b'a', b""));
-}
-
-#[test]
-fn no_match_reversed() {
-    assert_eq!(None, memrchr(b'a', b"xyz"));
-}
-
-#[test]
-fn each_alignment_reversed() {
-    let mut data = [1u8; 64];
-    let needle = 2;
-    let pos = 40;
-    data[pos] = needle;
-    for start in 0..16 {
-        assert_eq!(Some(pos - start), memrchr(needle, &data[start..]));
-    }
-}

src/libcore/tests/lib.rs

@@ -46,6 +46,7 @@
 #![feature(reverse_bits)]
 #![feature(inclusive_range_methods)]
 #![feature(iterator_find_map)]
+#![feature(slice_internals)]
 
 extern crate core;
 extern crate test;
@@ -74,4 +75,5 @@ mod result;
 mod slice;
 mod str;
 mod str_lossy;
+mod time;
 mod tuple;

src/libcore/tests/num/uint_macros.rs

@@ -98,6 +98,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg(not(stage0))]
     fn test_reverse_bits() {
         assert_eq!(A.reverse_bits().reverse_bits(), A);
         assert_eq!(B.reverse_bits().reverse_bits(), B);

src/libcore/tests/slice.rs

@@ -550,3 +550,89 @@ fn sort_unstable() {
     v.sort_unstable();
     assert!(v == [0xDEADBEEF]);
 }
+
+pub mod memchr {
+    use core::slice::memchr::{memchr, memrchr};
+
+    // test fallback implementations on all platforms
+    #[test]
+    fn matches_one() {
+        assert_eq!(Some(0), memchr(b'a', b"a"));
+    }
+
+    #[test]
+    fn matches_begin() {
+        assert_eq!(Some(0), memchr(b'a', b"aaaa"));
+    }
+
+    #[test]
+    fn matches_end() {
+        assert_eq!(Some(4), memchr(b'z', b"aaaaz"));
+    }
+
+    #[test]
+    fn matches_nul() {
+        assert_eq!(Some(4), memchr(b'\x00', b"aaaa\x00"));
+    }
+
+    #[test]
+    fn matches_past_nul() {
+        assert_eq!(Some(5), memchr(b'z', b"aaaa\x00z"));
+    }
+
+    #[test]
+    fn no_match_empty() {
+        assert_eq!(None, memchr(b'a', b""));
+    }
+
+    #[test]
+    fn no_match() {
+        assert_eq!(None, memchr(b'a', b"xyz"));
+    }
+
+    #[test]
+    fn matches_one_reversed() {
+        assert_eq!(Some(0), memrchr(b'a', b"a"));
+    }
+
+    #[test]
+    fn matches_begin_reversed() {
+        assert_eq!(Some(3), memrchr(b'a', b"aaaa"));
+    }
+
+    #[test]
+    fn matches_end_reversed() {
+        assert_eq!(Some(0), memrchr(b'z', b"zaaaa"));
+    }
+
+    #[test]
+    fn matches_nul_reversed() {
+        assert_eq!(Some(4), memrchr(b'\x00', b"aaaa\x00"));
+    }
+
+    #[test]
+    fn matches_past_nul_reversed() {
+        assert_eq!(Some(0), memrchr(b'z', b"z\x00aaaa"));
+    }
+
+    #[test]
+    fn no_match_empty_reversed() {
+        assert_eq!(None, memrchr(b'a', b""));
+    }
+
+    #[test]
+    fn no_match_reversed() {
+        assert_eq!(None, memrchr(b'a', b"xyz"));
+    }
+
+    #[test]
+    fn each_alignment_reversed() {
+        let mut data = [1u8; 64];
+        let needle = 2;
+        let pos = 40;
+        data[pos] = needle;
+        for start in 0..16 {
+            assert_eq!(Some(pos - start), memrchr(needle, &data[start..]));
+        }
+    }
+}

src/libcore/tests/time.rs

@@ -0,0 +1,124 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use core::time::Duration;
+
+#[test]
+fn creation() {
+    assert!(Duration::from_secs(1) != Duration::from_secs(0));
+    assert_eq!(Duration::from_secs(1) + Duration::from_secs(2),
+               Duration::from_secs(3));
+    assert_eq!(Duration::from_millis(10) + Duration::from_secs(4),
+               Duration::new(4, 10 * 1_000_000));
+    assert_eq!(Duration::from_millis(4000), Duration::new(4, 0));
+}
+
+#[test]
+fn secs() {
+    assert_eq!(Duration::new(0, 0).as_secs(), 0);
+    assert_eq!(Duration::from_secs(1).as_secs(), 1);
+    assert_eq!(Duration::from_millis(999).as_secs(), 0);
+    assert_eq!(Duration::from_millis(1001).as_secs(), 1);
+}
+
+#[test]
+fn nanos() {
+    assert_eq!(Duration::new(0, 0).subsec_nanos(), 0);
+    assert_eq!(Duration::new(0, 5).subsec_nanos(), 5);
+    assert_eq!(Duration::new(0, 1_000_000_001).subsec_nanos(), 1);
+    assert_eq!(Duration::from_secs(1).subsec_nanos(), 0);
+    assert_eq!(Duration::from_millis(999).subsec_nanos(), 999 * 1_000_000);
+    assert_eq!(Duration::from_millis(1001).subsec_nanos(), 1 * 1_000_000);
+}
+
+#[test]
+fn add() {
+    assert_eq!(Duration::new(0, 0) + Duration::new(0, 1),
+               Duration::new(0, 1));
+    assert_eq!(Duration::new(0, 500_000_000) + Duration::new(0, 500_000_001),
+               Duration::new(1, 1));
+}
+
+#[test]
+fn checked_add() {
+    assert_eq!(Duration::new(0, 0).checked_add(Duration::new(0, 1)),
+               Some(Duration::new(0, 1)));
+    assert_eq!(Duration::new(0, 500_000_000).checked_add(Duration::new(0, 500_000_001)),
+               Some(Duration::new(1, 1)));
+    assert_eq!(Duration::new(1, 0).checked_add(Duration::new(::core::u64::MAX, 0)), None);
+}
+
+#[test]
+fn sub() {
+    assert_eq!(Duration::new(0, 1) - Duration::new(0, 0),
+               Duration::new(0, 1));
+    assert_eq!(Duration::new(0, 500_000_001) - Duration::new(0, 500_000_000),
+               Duration::new(0, 1));
+    assert_eq!(Duration::new(1, 0) - Duration::new(0, 1),
+               Duration::new(0, 999_999_999));
+}
+
+#[test]
+fn checked_sub() {
+    let zero = Duration::new(0, 0);
+    let one_nano = Duration::new(0, 1);
+    let one_sec = Duration::new(1, 0);
+    assert_eq!(one_nano.checked_sub(zero), Some(Duration::new(0, 1)));
+    assert_eq!(one_sec.checked_sub(one_nano),
+               Some(Duration::new(0, 999_999_999)));
+    assert_eq!(zero.checked_sub(one_nano), None);
+    assert_eq!(zero.checked_sub(one_sec), None);
+}
+
+#[test]
+#[should_panic]
+fn sub_bad1() {
+    let _ = Duration::new(0, 0) - Duration::new(0, 1);
+}
+
+#[test]
+#[should_panic]
+fn sub_bad2() {
+    let _ = Duration::new(0, 0) - Duration::new(1, 0);
+}
+
+#[test]
+fn mul() {
+    assert_eq!(Duration::new(0, 1) * 2, Duration::new(0, 2));
+    assert_eq!(Duration::new(1, 1) * 3, Duration::new(3, 3));
+    assert_eq!(Duration::new(0, 500_000_001) * 4, Duration::new(2, 4));
+    assert_eq!(Duration::new(0, 500_000_001) * 4000,
+               Duration::new(2000, 4000));
+}
+
+#[test]
+fn checked_mul() {
+    assert_eq!(Duration::new(0, 1).checked_mul(2), Some(Duration::new(0, 2)));
+    assert_eq!(Duration::new(1, 1).checked_mul(3), Some(Duration::new(3, 3)));
+    assert_eq!(Duration::new(0, 500_000_001).checked_mul(4), Some(Duration::new(2, 4)));
+    assert_eq!(Duration::new(0, 500_000_001).checked_mul(4000),
+               Some(Duration::new(2000, 4000)));
+    assert_eq!(Duration::new(::core::u64::MAX - 1, 0).checked_mul(2), None);
+}
+
+#[test]
+fn div() {
+    assert_eq!(Duration::new(0, 1) / 2, Duration::new(0, 0));
+    assert_eq!(Duration::new(1, 1) / 3, Duration::new(0, 333_333_333));
+    assert_eq!(Duration::new(99, 999_999_000) / 100,
+               Duration::new(0, 999_999_990));
+}
+
+#[test]
+fn checked_div() {
+    assert_eq!(Duration::new(2, 0).checked_div(2), Some(Duration::new(1, 0)));
+    assert_eq!(Duration::new(1, 0).checked_div(2), Some(Duration::new(0, 500_000_000)));
+    assert_eq!(Duration::new(2, 0).checked_div(0), None);
+}

src/libcore/time.rs

@@ -481,119 +481,3 @@ impl<'a> Sum<&'a Duration> for Duration {
         iter.fold(Duration::new(0, 0), |a, b| a + *b)
     }
 }
-
-#[cfg(test)]
-mod tests {
-    use super::Duration;
-
-    #[test]
-    fn creation() {
-        assert!(Duration::from_secs(1) != Duration::from_secs(0));
-        assert_eq!(Duration::from_secs(1) + Duration::from_secs(2),
-                   Duration::from_secs(3));
-        assert_eq!(Duration::from_millis(10) + Duration::from_secs(4),
-                   Duration::new(4, 10 * 1_000_000));
-        assert_eq!(Duration::from_millis(4000), Duration::new(4, 0));
-    }
-
-    #[test]
-    fn secs() {
-        assert_eq!(Duration::new(0, 0).as_secs(), 0);
-        assert_eq!(Duration::from_secs(1).as_secs(), 1);
-        assert_eq!(Duration::from_millis(999).as_secs(), 0);
-        assert_eq!(Duration::from_millis(1001).as_secs(), 1);
-    }
-
-    #[test]
-    fn nanos() {
-        assert_eq!(Duration::new(0, 0).subsec_nanos(), 0);
-        assert_eq!(Duration::new(0, 5).subsec_nanos(), 5);
-        assert_eq!(Duration::new(0, 1_000_000_001).subsec_nanos(), 1);
-        assert_eq!(Duration::from_secs(1).subsec_nanos(), 0);
-        assert_eq!(Duration::from_millis(999).subsec_nanos(), 999 * 1_000_000);
-        assert_eq!(Duration::from_millis(1001).subsec_nanos(), 1 * 1_000_000);
-    }
-
-    #[test]
-    fn add() {
-        assert_eq!(Duration::new(0, 0) + Duration::new(0, 1),
-                   Duration::new(0, 1));
-        assert_eq!(Duration::new(0, 500_000_000) + Duration::new(0, 500_000_001),
-                   Duration::new(1, 1));
-    }
-
-    #[test]
-    fn checked_add() {
-        assert_eq!(Duration::new(0, 0).checked_add(Duration::new(0, 1)),
-                   Some(Duration::new(0, 1)));
-        assert_eq!(Duration::new(0, 500_000_000).checked_add(Duration::new(0, 500_000_001)),
-                   Some(Duration::new(1, 1)));
-        assert_eq!(Duration::new(1, 0).checked_add(Duration::new(::u64::MAX, 0)), None);
-    }
-
-    #[test]
-    fn sub() {
-        assert_eq!(Duration::new(0, 1) - Duration::new(0, 0),
-                   Duration::new(0, 1));
-        assert_eq!(Duration::new(0, 500_000_001) - Duration::new(0, 500_000_000),
-                   Duration::new(0, 1));
-        assert_eq!(Duration::new(1, 0) - Duration::new(0, 1),
-                   Duration::new(0, 999_999_999));
-    }
-
-    #[test]
-    fn checked_sub() {
-        let zero = Duration::new(0, 0);
-        let one_nano = Duration::new(0, 1);
-        let one_sec = Duration::new(1, 0);
-        assert_eq!(one_nano.checked_sub(zero), Some(Duration::new(0, 1)));
-        assert_eq!(one_sec.checked_sub(one_nano),
-                   Some(Duration::new(0, 999_999_999)));
-        assert_eq!(zero.checked_sub(one_nano), None);
-        assert_eq!(zero.checked_sub(one_sec), None);
-    }
-
-    #[test] #[should_panic]
-    fn sub_bad1() {
-        Duration::new(0, 0) - Duration::new(0, 1);
-    }
-
-    #[test] #[should_panic]
-    fn sub_bad2() {
-        Duration::new(0, 0) - Duration::new(1, 0);
-    }
-
-    #[test]
-    fn mul() {
-        assert_eq!(Duration::new(0, 1) * 2, Duration::new(0, 2));
-        assert_eq!(Duration::new(1, 1) * 3, Duration::new(3, 3));
-        assert_eq!(Duration::new(0, 500_000_001) * 4, Duration::new(2, 4));
-        assert_eq!(Duration::new(0, 500_000_001) * 4000,
-                   Duration::new(2000, 4000));
-    }
-
-    #[test]
-    fn checked_mul() {
-        assert_eq!(Duration::new(0, 1).checked_mul(2), Some(Duration::new(0, 2)));
-        assert_eq!(Duration::new(1, 1).checked_mul(3), Some(Duration::new(3, 3)));
-        assert_eq!(Duration::new(0, 500_000_001).checked_mul(4), Some(Duration::new(2, 4)));
-        assert_eq!(Duration::new(0, 500_000_001).checked_mul(4000),
-                   Some(Duration::new(2000, 4000)));
-        assert_eq!(Duration::new(::u64::MAX - 1, 0).checked_mul(2), None);
-    }
-
-    #[test]
-    fn div() {
-        assert_eq!(Duration::new(0, 1) / 2, Duration::new(0, 0));
-        assert_eq!(Duration::new(1, 1) / 3, Duration::new(0, 333_333_333));
-        assert_eq!(Duration::new(99, 999_999_000) / 100,
-                   Duration::new(0, 999_999_990));
-    }
-
-    #[test]
-    fn checked_div() {
-        assert_eq!(Duration::new(2, 0).checked_div(2), Some(Duration::new(1, 0)));
-        assert_eq!(Duration::new(1, 0).checked_div(2), Some(Duration::new(0, 500_000_000)));
-        assert_eq!(Duration::new(2, 0).checked_div(0), None);
-    }
-}

src/libstd/lib.rs

@@ -330,10 +330,10 @@
 // with a rustc without jemalloc.
 // FIXME(#44236) shouldn't need MSVC logic
 #![cfg_attr(all(not(target_env = "msvc"),
-                any(stage0, feature = "force_alloc_system")),
+                any(all(stage0, not(test)), feature = "force_alloc_system")),
             feature(global_allocator))]
 #[cfg(all(not(target_env = "msvc"),
-          any(stage0, feature = "force_alloc_system")))]
+          any(all(stage0, not(test)), feature = "force_alloc_system")))]
 #[global_allocator]
 static ALLOC: alloc_system::System = alloc_system::System;
 

src/tools/tidy/src/lib.rs

@@ -51,6 +51,7 @@ pub mod pal;
 pub mod deps;
 pub mod ui_tests;
 pub mod unstable_book;
+pub mod libcoretest;
 
 fn filter_dirs(path: &Path) -> bool {
     let skip = [

src/tools/tidy/src/libcoretest.rs

@@ -0,0 +1,34 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Tidy check to ensure `#[test]` is not used directly inside `libcore`.
+//!
+//! `#![no_core]` libraries cannot be tested directly due to duplicating lang
+//! item. All tests must be written externally in `libcore/tests`.
+
+use std::path::Path;
+use std::fs::read_to_string;
+
+pub fn check(path: &Path, bad: &mut bool) {
+    let libcore_path = path.join("libcore");
+    super::walk(
+        &libcore_path,
+        &mut |subpath| t!(subpath.strip_prefix(&libcore_path)).starts_with("tests"),
+        &mut |subpath| {
+            if t!(read_to_string(subpath)).contains("#[test]") {
+                tidy_error!(
+                    bad,
+                    "{} contains #[test]; libcore tests must be placed inside `src/libcore/tests/`",
+                    subpath.display()
+                );
+            }
+        },
+    );
+}

src/tools/tidy/src/main.rs

@@ -41,6 +41,7 @@ fn main() {
     features::check(&path, &mut bad, quiet);
     pal::check(&path, &mut bad);
     unstable_book::check(&path, &mut bad);
+    libcoretest::check(&path, &mut bad);
     if !args.iter().any(|s| *s == "--no-vendor") {
         deps::check(&path, &mut bad);
     }