Fix occasional test failure due to env::set_var with multiple test threads

ci/azure-steps.yml

@@ -16,9 +16,9 @@ steps:
 
   - script: cargo build
     displayName: "Normal build"
-  - bash: cargo test $NO_RUN -- --test-threads 1
+  - bash: cargo test $NO_RUN
     displayName: "Crate tests"
-  - bash: cargo test $NO_RUN --features parallel -- --test-threads 1
+  - bash: cargo test $NO_RUN --features parallel
     displayName: "Crate tests (parallel)"
   - bash: cargo test $NO_RUN --manifest-path cc-test/Cargo.toml --target $TARGET
     displayName: "cc-test tests"

tests/cflags.rs

@@ -0,0 +1,18 @@
+extern crate cc;
+extern crate tempdir;
+
+mod support;
+
+use std::env;
+use support::Test;
+
+/// This test is in its own module because it modifies the environment and would affect other tests
+/// when run in parallel with them.
+#[test]
+fn gnu_no_warnings_if_cflags() {
+    env::set_var("CFLAGS", "-arbitrary");
+    let test = Test::gnu();
+    test.gcc().file("foo.c").compile("foo");
+
+    test.cmd(0).must_not_have("-Wall").must_not_have("-Wextra");
+}

tests/cxxflags.rs

@@ -0,0 +1,18 @@
+extern crate cc;
+extern crate tempdir;
+
+mod support;
+
+use std::env;
+use support::Test;
+
+/// This test is in its own module because it modifies the environment and would affect other tests
+/// when run in parallel with them.
+#[test]
+fn gnu_no_warnings_if_cxxflags() {
+    env::set_var("CXXFLAGS", "-arbitrary");
+    let test = Test::gnu();
+    test.gcc().file("foo.cpp").cpp(true).compile("foo");
+
+    test.cmd(0).must_not_have("-Wall").must_not_have("-Wextra");
+}

tests/support/mod.rs

@@ -3,8 +3,9 @@
 use std::env;
 use std::ffi::{OsStr, OsString};
 use std::fs::{self, File};
+use std::io;
 use std::io::prelude::*;
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 
 use cc;
 use tempdir::TempDir;
@@ -49,10 +50,13 @@ impl Test {
     }
 
     pub fn shim(&self, name: &str) -> &Test {
-        let fname = format!("{}{}", name, env::consts::EXE_SUFFIX);
-        fs::hard_link(&self.gcc, self.td.path().join(&fname))
-            .or_else(|_| fs::copy(&self.gcc, self.td.path().join(&fname)).map(|_| ()))
-            .unwrap();
+        link_or_copy(
+            &self.gcc,
+            self.td
+                .path()
+                .join(&format!("{}{}", name, env::consts::EXE_SUFFIX)),
+        )
+        .unwrap();
         self
     }
 
@@ -136,3 +140,22 @@ impl Execution {
         self
     }
 }
+
+/// Hard link an executable or copy it if that fails.
+///
+/// We first try to hard link an executable to save space. If that fails (as on Windows with
+/// different mount points, issue #60), we copy.
+#[cfg(not(target_os = "macos"))]
+fn link_or_copy<P: AsRef<Path>, Q: AsRef<Path>>(from: P, to: Q) -> io::Result<()> {
+    let from = from.as_ref();
+    let to = to.as_ref();
+    fs::hard_link(from, to).or_else(|_| fs::copy(from, to).map(|_| ()))
+}
+
+/// Copy an executable.
+///
+/// On macOS, hard linking the executable leads to strange failures (issue #419), so we just copy.
+#[cfg(target_os = "macos")]
+fn link_or_copy<P: AsRef<Path>, Q: AsRef<Path>>(from: P, to: Q) -> io::Result<()> {
+    fs::copy(from, to).map(|_| ())
+}

tests/test.rs

@@ -1,7 +1,6 @@
 extern crate cc;
 extern crate tempdir;
 
-use std::env;
 use support::Test;
 
 mod support;
@@ -111,26 +110,6 @@ fn gnu_warnings_overridable() {
         .must_have_in_order("-Wall", "-Wno-missing-field-initializers");
 }
 
-#[test]
-fn gnu_no_warnings_if_cflags() {
-    env::set_var("CFLAGS", "-Wflag-does-not-exist");
-    let test = Test::gnu();
-    test.gcc().file("foo.c").compile("foo");
-
-    test.cmd(0).must_not_have("-Wall").must_not_have("-Wextra");
-    env::set_var("CFLAGS", "");
-}
-
-#[test]
-fn gnu_no_warnings_if_cxxflags() {
-    env::set_var("CXXFLAGS", "-Wflag-does-not-exist");
-    let test = Test::gnu();
-    test.gcc().file("foo.c").compile("foo");
-
-    test.cmd(0).must_not_have("-Wall").must_not_have("-Wextra");
-    env::set_var("CXXFLAGS", "");
-}
-
 #[test]
 fn gnu_x86_64() {
     for vendor in &["unknown-linux-gnu", "apple-darwin"] {