Fix spurious Windows errors with switch_features_rerun.

Author: ehuss

tests/testsuite/build_script.rs

@@ -3171,9 +3171,12 @@ fn switch_features_rerun() {
         )
         .build();
 
-    p.cargo("run -v --features=foo").with_stdout("foo\n").run();
-    p.cargo("run -v").with_stdout("bar\n").run();
-    p.cargo("run -v --features=foo").with_stdout("foo\n").run();
+    p.cargo("build -v --features=foo").run();
+    p.safely_rename_run("foo", "with_foo").with_stdout("foo\n").run();
+    p.cargo("build -v").run();
+    p.safely_rename_run("foo", "without_foo").with_stdout("bar\n").run();
+    p.cargo("build -v --features=foo").run();
+    p.safely_rename_run("foo", "with_foo2").with_stdout("foo\n").run();
 }
 
 #[test]

tests/testsuite/freshness.rs

@@ -447,17 +447,6 @@ fn changing_bin_features_caches_targets() {
         )
         .build();
 
-    // Windows has a problem with replacing a binary that was just executed.
-    // Unlinking it will succeed, but then attempting to immediately replace
-    // it will sometimes fail with "Already Exists".
-    // See https://github.com/rust-lang/cargo/issues/5481
-    let foo_proc = |name: &str| {
-        let src = p.bin("foo");
-        let dst = p.bin(name);
-        fs::rename(&src, &dst).expect("Failed to rename foo");
-        p.process(dst)
-    };
-
     p.cargo("build")
         .with_stderr(
             "\
@@ -466,7 +455,7 @@ fn changing_bin_features_caches_targets() {
 ",
         )
         .run();
-    foo_proc("off1").with_stdout("feature off").run();
+    p.safely_rename_run("foo", "off1").with_stdout("feature off").run();
 
     p.cargo("build --features foo")
         .with_stderr(
@@ -476,7 +465,7 @@ fn changing_bin_features_caches_targets() {
 ",
         )
         .run();
-    foo_proc("on1").with_stdout("feature on").run();
+    p.safely_rename_run("foo", "on1").with_stdout("feature on").run();
 
     /* Targets should be cached from the first build */
 
@@ -487,7 +476,7 @@ fn changing_bin_features_caches_targets() {
 ",
         )
         .run();
-    foo_proc("off2").with_stdout("feature off").run();
+    p.safely_rename_run("foo", "off2").with_stdout("feature off").run();
 
     p.cargo("build --features foo")
         .with_stderr(
@@ -496,7 +485,7 @@ fn changing_bin_features_caches_targets() {
 ",
         )
         .run();
-    foo_proc("on2").with_stdout("feature on").run();
+    p.safely_rename_run("foo", "on2").with_stdout("feature on").run();
 }
 
 #[test]

tests/testsuite/support/mod.rs

@@ -399,6 +399,27 @@ impl Project {
         execs
     }
 
+    /// Safely run a process after `cargo build`.
+    ///
+    /// Windows has a problem where a process cannot be reliably
+    /// be replaced, removed, or renamed immediately after executing it.
+    /// The action may fail (with errors like Access is denied), or
+    /// it may succeed, but future attempts to use the same filename
+    /// will fail with "Already Exists".
+    ///
+    /// If you have a test that needs to do `cargo run` multiple
+    /// times, you should instead use `cargo build` and use this
+    /// method to run the executable. Each time you call this,
+    /// use a new name for `dst`.
+    /// See https://github.com/rust-lang/cargo/issues/5481
+    pub fn safely_rename_run(&self, src: &str, dst: &str) -> Execs {
+        let src = self.bin(src);
+        let dst = self.bin(dst);
+        fs::rename(&src, &dst)
+            .unwrap_or_else(|e| panic!("Failed to rename `{:?}` to `{:?}`: {}", src, dst, e));
+        self.process(dst)
+    }
+
     /// Returns the contents of `Cargo.lock`.
     pub fn read_lockfile(&self) -> String {
         self.read_file("Cargo.lock")