walkdir: fix root symlink bug

This commit fixes a nasty bug where the root path given to walkdir was
always reported as a symlink, even when 'follow_links' was enabled. This
appears to be a regression introduced by commit 6f72fce as part of
fixing BurntSushi/ripgrep#984.

The central problem was that since root paths should always be followed,
we were creating a DirEntry whose internal file type was always resolved
by following a symlink, but whose 'metadata' method still returned the
metadata of the symlink and not the target. This was problematic and
inconsistent both with and without 'follow_links' enabled.

We also fix the documentation. In particular, we make the docs of 'new'
more unambiguous, where it previously could have been interpreted as
contradictory to the docs on 'DirEntry'. Specifically, 'WalkDir::new'
says:

    If root is a symlink, then it is always followed.

But the docs for 'DirEntry::metadata' say

    This always calls std::fs::symlink_metadata.

    If this entry is a symbolic link and follow_links is enabled, then
    std::fs::metadata is called instead.

Similarly, 'DirEntry::file_type' said

    If this is a symbolic link and follow_links is true, then this
    returns the type of the target.

That is, if 'root' is a symlink and 'follow_links' is NOT enabled,
then the previous incorrect behavior resulted in 'DirEntry::file_type'
behaving as if 'follow_links' was enabled. If 'follow_links'
was enabled, then the previous incorrect behavior resulted in
'DirEntry::metadata' reporting the metadata of the symlink itself.

We fix this by correctly constructing the DirEntry in the first place,
and then adding special case logic to path traversal that will always
attempt to follow the root path if it's a symlink and 'follow_links'
was not enabled. We also tweak the docs on 'WalkDir::new' to be more
precise.

Fixes #115

1 files changed, 45 insertions, 0 deletions

diff --git a/src/tests.rs b/src/tests.rs
index 1fb7682..ddce795 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -531,6 +531,51 @@ fn first_path_not_symlink() {
     assert!(!dents[0].path_is_symlink());
 }
 
+// Like first_path_not_symlink, but checks that the first path is not reported
+// as a symlink even when we are supposed to be following them.
+#[test]
+#[cfg(unix)]
+fn first_path_not_symlink_follow() {
+    let exp = td("foo", vec![]);
+    let (tmp, _got) = dir_setup(&exp);
+
+    let dents = WalkDir::new(tmp.path().join("foo"))
+        .follow_links(true)
+        .into_iter()
+        .collect::<Result<Vec<_>, _>>()
+        .unwrap();
+    assert_eq!(1, dents.len());
+    assert!(!dents[0].path_is_symlink());
+}
+
+// See: https://github.com/BurntSushi/walkdir/issues/115
+#[test]
+#[cfg(unix)]
+fn first_path_is_followed() {
+    let exp = td("foo", vec![
+        td("a", vec![tf("a1"), tf("a2")]),
+        td("b", vec![tlf("../a/a1", "alink")]),
+    ]);
+    let (tmp, _got) = dir_setup(&exp);
+
+    let dents = WalkDir::new(tmp.path().join("foo/b/alink"))
+        .into_iter()
+        .collect::<Result<Vec<_>, _>>()
+        .unwrap();
+    assert_eq!(1, dents.len());
+    assert!(dents[0].file_type().is_symlink());
+    assert!(dents[0].metadata().unwrap().file_type().is_symlink());
+
+    let dents = WalkDir::new(tmp.path().join("foo/b/alink"))
+        .follow_links(true)
+        .into_iter()
+        .collect::<Result<Vec<_>, _>>()
+        .unwrap();
+    assert_eq!(1, dents.len());
+    assert!(!dents[0].file_type().is_symlink());
+    assert!(!dents[0].metadata().unwrap().file_type().is_symlink());
+}
+
 #[test]
 #[cfg(unix)]
 fn walk_dir_sym_detect_no_follow_no_loop() {