fix: always use absolute paths (#323)

We used absolute paths in the builder when making directories and in
`create_named` but this didn't cover `Builder::make_in` and technically
introduced a small race in some unnamed tempfile cases (i.e., when we
can't atomically create unnamed temporary files and need to create then
immediately delete them).

Instead, we now resolve the filename into an absolute path inside the
main create helper.

Author: Stebalien

src/file/mod.rs

@@ -1043,16 +1043,11 @@ impl<F: AsRawHandle> AsRawHandle for NamedTempFile<F> {
 }
 
 pub(crate) fn create_named(
-    mut path: PathBuf,
+    path: PathBuf,
     open_options: &mut OpenOptions,
     permissions: Option<&std::fs::Permissions>,
     keep: bool,
 ) -> io::Result<NamedTempFile> {
-    // Make the path absolute. Otherwise, changing directories could cause us to
-    // delete the wrong file.
-    if !path.is_absolute() {
-        path = std::env::current_dir()?.join(path)
-    }
     imp::create_named(&path, open_options, permissions)
         .with_err_path(|| path.clone())
         .map(|file| NamedTempFile {

src/lib.rs

@@ -604,17 +604,13 @@ impl<'a, 'b> Builder<'a, 'b> {
     ///
     /// [resource-leaking]: struct.TempDir.html#resource-leaking
     pub fn tempdir_in<P: AsRef<Path>>(&self, dir: P) -> io::Result<TempDir> {
-        let storage;
-        let mut dir = dir.as_ref();
-        if !dir.is_absolute() {
-            let cur_dir = std::env::current_dir()?;
-            storage = cur_dir.join(dir);
-            dir = &storage;
-        }
-
-        util::create_helper(dir, self.prefix, self.suffix, self.random_len, |path| {
-            dir::create(path, self.permissions.as_ref(), self.keep)
-        })
+        util::create_helper(
+            dir.as_ref(),
+            self.prefix,
+            self.suffix,
+            self.random_len,
+            |path| dir::create(path, self.permissions.as_ref(), self.keep),
+        )
     }
 
     /// Attempts to create a temporary file (or file-like object) using the

src/util.rs

@@ -26,6 +26,16 @@ pub fn create_helper<R>(
     random_len: usize,
     mut f: impl FnMut(PathBuf) -> io::Result<R>,
 ) -> io::Result<R> {
+    // Make the path absolute. Otherwise, changing the current directory can invalidate a stored
+    // path (causing issues when cleaning up temporary files.
+    let mut base = &*base; // re-borrow to shrink lifetime
+    let base_path_storage; // slot to store the absolute path, if necessary.
+    if !base.is_absolute() {
+        let cur_dir = std::env::current_dir()?;
+        base_path_storage = cur_dir.join(base);
+        base = &base_path_storage;
+    }
+
     let num_retries = if random_len != 0 {
         crate::NUM_RETRIES
     } else {

tests/namedtempfile.rs

@@ -290,6 +290,16 @@ fn test_change_dir() {
     assert!(!exists(path))
 }
 
+#[test]
+fn test_change_dir_make() {
+    std::env::set_current_dir(env::temp_dir()).unwrap();
+    let tmpfile = Builder::new().make_in(".", |p| File::create(p)).unwrap();
+    let path = std::env::current_dir().unwrap().join(tmpfile.path());
+    std::env::set_current_dir("/").unwrap();
+    drop(tmpfile);
+    assert!(!exists(path))
+}
+
 #[test]
 fn test_into_parts() {
     let mut file = NamedTempFile::new().unwrap();