Don't rely on a thread local to uniquely create test roots

.gitignore

@@ -1,4 +1,5 @@
 /target
+/tests/testsuite/support/cargo-test-macro/target
 Cargo.lock
 .cargo
 /config.stamp

Cargo.toml

@@ -104,6 +104,7 @@ features = [
 bufstream = "0.1"
 proptest = "0.9.1"
 varisat = "0.2.1"
+cargo-test-macro = { "path" = "tests/testsuite/support/cargo-test-macro" }
 
 [[bin]]
 name = "cargo"

tests/testsuite/main.rs

@@ -6,6 +6,9 @@
 #![warn(clippy::needless_borrow)]
 #![warn(clippy::redundant_clone)]
 
+#[macro_use]
+extern crate cargo_test_macro;
+
 #[macro_use]
 mod support;
 

tests/testsuite/support/cargo-test-macro/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "cargo-test-macro"
+version = "0.1.0"
+authors = ["Jethro Beekman <jethro@fortanix.com>"]
+edition = "2018"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+quote = "0.6"
+syn = { version = "0.15", features = ["full"] }

tests/testsuite/support/cargo-test-macro/src/lib.rs

@@ -0,0 +1,24 @@
+extern crate proc_macro;
+
+use quote::{quote, ToTokens};
+use syn::{*, parse::Parser};
+
+#[proc_macro_attribute]
+pub fn cargo_test(
+    _attr: proc_macro::TokenStream,
+    item: proc_macro::TokenStream,
+) -> proc_macro::TokenStream {
+    let mut fn_def = parse_macro_input!(item as ItemFn);
+
+    let attr = quote! {
+        #[test]
+    };
+    fn_def.attrs.extend(Attribute::parse_outer.parse2(attr).unwrap());
+
+    let stmt = quote! {
+        let _test_guard = crate::support::paths::init_root();
+    };
+    fn_def.block.stmts.insert(0, parse2(stmt).unwrap());
+
+    fn_def.into_token_stream().into()
+}

tests/testsuite/support/paths.rs

@@ -1,58 +1,93 @@
-use std::cell::Cell;
+use std::cell::RefCell;
+use std::collections::HashMap;
 use std::env;
 use std::fs;
 use std::io::{self, ErrorKind};
 use std::path::{Path, PathBuf};
 use std::sync::atomic::{AtomicUsize, Ordering};
-use std::sync::{Once, ONCE_INIT};
+use std::sync::Mutex;
 
 use filetime::{self, FileTime};
+use lazy_static::lazy_static;
 
 static CARGO_INTEGRATION_TEST_DIR: &'static str = "cit";
-static NEXT_ID: AtomicUsize = AtomicUsize::new(0);
 
-thread_local!(static TASK_ID: usize = NEXT_ID.fetch_add(1, Ordering::SeqCst));
+lazy_static! {
+    static ref GLOBAL_ROOT: PathBuf = {
+        let mut path = t!(env::current_exe());
+        path.pop(); // chop off exe name
+        path.pop(); // chop off 'debug'
 
-fn init() {
-    static GLOBAL_INIT: Once = ONCE_INIT;
-    thread_local!(static LOCAL_INIT: Cell<bool> = Cell::new(false));
-    GLOBAL_INIT.call_once(|| {
-        global_root().mkdir_p();
-    });
-    LOCAL_INIT.with(|i| {
-        if i.get() {
-            return;
+        // If `cargo test` is run manually then our path looks like
+        // `target/debug/foo`, in which case our `path` is already pointing at
+        // `target`. If, however, `cargo test --target $target` is used then the
+        // output is `target/$target/debug/foo`, so our path is pointing at
+        // `target/$target`. Here we conditionally pop the `$target` name.
+        if path.file_name().and_then(|s| s.to_str()) != Some("target") {
+            path.pop();
         }
-        i.set(true);
-        root().rm_rf();
-        home().mkdir_p();
-    })
+
+        path.push(CARGO_INTEGRATION_TEST_DIR);
+
+        path.rm_rf();
+        path.mkdir_p();
+
+        path
+    };
+
+    static ref TEST_ROOTS: Mutex<HashMap<String, PathBuf>> = Default::default();
 }
 
-fn global_root() -> PathBuf {
-    let mut path = t!(env::current_exe());
-    path.pop(); // chop off exe name
-    path.pop(); // chop off 'debug'
+// We need to give each test a unique id. The test name could serve this
+// purpose, but the `test` crate doesn't have a way to obtain the current test
+// name.[*] Instead, we used the `cargo-test-macro` crate to automatically
+// insert an init function for each test that sets the test name in a thread
+// local variable.
+//
+// [*] It does set the thread name, but only when running concurrently. If not
+// running concurrently, all tests are run on the main thread.
+thread_local! {
+    static TEST_ID: RefCell<Option<usize>> = RefCell::new(None);
+}
 
-    // If `cargo test` is run manually then our path looks like
-    // `target/debug/foo`, in which case our `path` is already pointing at
-    // `target`. If, however, `cargo test --target $target` is used then the
-    // output is `target/$target/debug/foo`, so our path is pointing at
-    // `target/$target`. Here we conditionally pop the `$target` name.
-    if path.file_name().and_then(|s| s.to_str()) != Some("target") {
-        path.pop();
+pub struct TestIdGuard {
+    _private: ()
+}
+
+pub fn init_root() -> TestIdGuard {
+    static NEXT_ID: AtomicUsize = AtomicUsize::new(0);
+
+    let id = NEXT_ID.fetch_add(1, Ordering::Relaxed);
+    TEST_ID.with(|n| { *n.borrow_mut() = Some(id) } );
+
+    let guard = TestIdGuard {
+        _private: ()
+    };
+
+    root().mkdir_p();
+
+    guard
+}
+
+impl Drop for TestIdGuard {
+    fn drop(&mut self) {
+        TEST_ID.with(|n| { *n.borrow_mut() = None } );
     }
-
-    path.join(CARGO_INTEGRATION_TEST_DIR)
 }
 
 pub fn root() -> PathBuf {
-    init();
-    global_root().join(&TASK_ID.with(|my_id| format!("t{}", my_id)))
+    let id = TEST_ID.with(|n| {
+        n.borrow().expect("Tests must use the `#[cargo_test]` attribute in \
+                            order to be able to use the crate root.")
+    } );
+    GLOBAL_ROOT.join(&format!("t{}", id))
 }
 
 pub fn home() -> PathBuf {
-    root().join("home")
+    let mut path = root();
+    path.push("home");
+    path.mkdir_p();
+    path
 }
 
 pub trait CargoPathExt {