ignore: correctly detect hidden files on Windows

This commit fixes a bug where ripgrep only treated files beginning with
a `.` as hidden. On Windows, we continue this tradition, but
additionally check whether a file has the special Windows "hidden"
attribute set. If so, we treat it as a hidden file.

In order to make this work without an additional stat call, we had to
rearrange some of the plumbing from the directory traverser.

Fixes #1154

ignore/src/pathutil.rs

@@ -1,22 +1,56 @@
 use std::ffi::OsStr;
 use std::path::Path;
 
-/// Returns true if and only if this file path is considered to be hidden.
+use walk::DirEntry;
+
+/// Returns true if and only if this entry is considered to be hidden.
+///
+/// This only returns true if the base name of the path starts with a `.`.
+///
+/// On Unix, this implements a more optimized check.
 #[cfg(unix)]
-pub fn is_hidden<P: AsRef<Path>>(path: P) -> bool {
+pub fn is_hidden(dent: &DirEntry) -> bool {
     use std::os::unix::ffi::OsStrExt;
 
-    if let Some(name) = file_name(path.as_ref()) {
+    if let Some(name) = file_name(dent.path()) {
         name.as_bytes().get(0) == Some(&b'.')
     } else {
         false
     }
 }
 
-/// Returns true if and only if this file path is considered to be hidden.
-#[cfg(not(unix))]
-pub fn is_hidden<P: AsRef<Path>>(path: P) -> bool {
-    if let Some(name) = file_name(path.as_ref()) {
+/// Returns true if and only if this entry is considered to be hidden.
+///
+/// On Windows, this returns true if one of the following is true:
+///
+/// * The base name of the path starts with a `.`.
+/// * The file attributes have the `HIDDEN` property set.
+#[cfg(windows)]
+pub fn is_hidden(dent: &DirEntry) -> bool {
+    use std::os::windows::fs::MetadataExt;
+    use winapi_util::file;
+
+    // This looks like we're doing an extra stat call, but on Windows, the
+    // directory traverser reuses the metadata retrieved from each directory
+    // entry and stores it on the DirEntry itself. So this is "free."
+    if let Ok(md) = dent.metadata() {
+        if file::is_hidden(md.file_attributes() as u64) {
+            return true;
+        }
+    }
+    if let Some(name) = file_name(dent.path()) {
+        name.to_str().map(|s| s.starts_with(".")).unwrap_or(false)
+    } else {
+        false
+    }
+}
+
+/// Returns true if and only if this entry is considered to be hidden.
+///
+/// This only returns true if the base name of the path starts with a `.`.
+#[cfg(not(any(unix, windows)))]
+pub fn is_hidden(dent: &DirEntry) -> bool {
+    if let Some(name) = file_name(dent.path()) {
         name.to_str().map(|s| s.starts_with(".")).unwrap_or(false)
     } else {
         false