Auto merge of rust-lang#7865 - ehuss:fix-rebuild_sub_package_then_whi…

…le_package, r=alexcrichton

Fix rebuild_sub_package_then_while_package on HFS.

This test was flaky on HFS ([azure failure](https://dev.azure.com/rust-lang/cargo/_build/results?buildId=20144&view=logs&j=a5e52b91-c83f-5429-4a68-c246fc63a4f7&t=d4864165-4be3-5e34-b483-a6b05303aa68&l=2018)), resulting in this error:

```
   Compiling foo v0.0.1 (/Users/runner/runners/2.164.7/work/1/s/target/cit/t750/foo)
error[E0460]: found possibly newer version of crate `b` which `a` depends on
 --> src/lib.rs:1:1
  |
1 | extern crate a; extern crate b; pub fn toplevel() {}
  | ^^^^^^^^^^^^^^^
  |
  = note: perhaps that crate needs to be recompiled?
  = note: the following crate versions were found:
          crate `b`: /Users/runner/runners/2.164.7/work/1/s/target/cit/t750/foo/target/debug/deps/libb-98160c67a5811c37.rlib
          crate `b`: /Users/runner/runners/2.164.7/work/1/s/target/cit/t750/foo/target/debug/deps/libb-98160c67a5811c37.rmeta
          crate `a`: /Users/runner/runners/2.164.7/work/1/s/target/cit/t750/foo/target/debug/deps/liba-7d2b9ccd932a36e9.rmeta
```

There are two race-condition bugs here.

Race 1: The second cargo build command (`cargo build -pb`) would sometimes not build, because it thought `b` is fresh.  This can happen when the first build finishes and changing `b/src/lib.rs` happen within the same second. (rust-lang#5918)  The test silently ignored this failure, this is not the cause of the CI failure, though.

Race 2: The first and second build commands work as expected.  The third build command fails because it thinks both `a` and `b` are "fresh".  However, `b` was just rebuilt, and `a` depends on it, so `a` should have been rebuilt.  It thinks `a` is fresh because `a`'s mtime is equal to `b` when `b` finishes compiling within the same second that the first build finished.

The solution here is to make sure the second step happens well after the first.  The underlying problem is rust-lang#5918.

tests/testsuite/freshness.rs

@@ -136,21 +136,49 @@ fn rebuild_sub_package_then_while_package() {
         .file("b/src/lib.rs", "")
         .build();
 
-    p.cargo("build").run();
+    p.cargo("build")
+        .with_stderr(
+            "\
+[COMPILING] b [..]
+[COMPILING] a [..]
+[COMPILING] foo [..]
+[FINISHED] dev [..]
+",
+        )
+        .run();
 
-    File::create(&p.root().join("b/src/lib.rs"))
-        .unwrap()
-        .write_all(br#"pub fn b() {}"#)
-        .unwrap();
+    if is_coarse_mtime() {
+        sleep_ms(1000);
+    }
+    p.change_file("b/src/lib.rs", "pub fn b() {}");
 
-    p.cargo("build -pb").run();
+    p.cargo("build -pb -v")
+        .with_stderr(
+            "\
+[COMPILING] b [..]
+[RUNNING] `rustc --crate-name b [..]
+[FINISHED] dev [..]
+",
+        )
+        .run();
 
-    File::create(&p.root().join("src/lib.rs"))
-        .unwrap()
-        .write_all(br#"extern crate a; extern crate b; pub fn toplevel() {}"#)
-        .unwrap();
+    p.change_file(
+        "src/lib.rs",
+        "extern crate a; extern crate b; pub fn toplevel() {}",
+    );
 
-    p.cargo("build").run();
+    p.cargo("build -v")
+        .with_stderr(
+            "\
+[FRESH] b [..]
+[COMPILING] a [..]
+[RUNNING] `rustc --crate-name a [..]
+[COMPILING] foo [..]
+[RUNNING] `rustc --crate-name foo [..]
+[FINISHED] dev [..]
+",
+        )
+        .run();
 }
 
 #[cargo_test]