Rework glob sets.

We try to reduce the pressure on regexes and offload some of it to
Aho-Corasick or exact lookups.

src/pathutil.rs

@@ -0,0 +1,80 @@
+/*!
+The pathutil module provides platform specific operations on paths that are
+typically faster than the same operations as provided in std::path. In
+particular, we really want to avoid the costly operation of parsing the path
+into its constituent components. We give up on Windows, but on Unix, we deal
+with the raw bytes directly.
+
+On large repositories (like chromium), this can have a ~25% performance
+improvement on just listing the files to search (!).
+*/
+use std::ffi::OsStr;
+use std::path::Path;
+
+/// Strip `prefix` from the `path` and return the remainder.
+///
+/// If `path` doesn't have a prefix `prefix`, then return `None`.
+#[cfg(unix)]
+pub fn strip_prefix<'a, P: AsRef<Path>>(
+    prefix: P,
+    path: &'a Path,
+) -> Option<&'a Path> {
+    use std::os::unix::ffi::OsStrExt;
+
+    let prefix = prefix.as_ref().as_os_str().as_bytes();
+    let path = path.as_os_str().as_bytes();
+    if prefix.len() > path.len() || prefix != &path[0..prefix.len()] {
+        None
+    } else {
+        Some(&Path::new(OsStr::from_bytes(&path[prefix.len()..])))
+    }
+}
+
+/// Strip `prefix` from the `path` and return the remainder.
+///
+/// If `path` doesn't have a prefix `prefix`, then return `None`.
+#[cfg(not(unix))]
+pub fn strip_prefix<'a>(prefix: &Path, path: &'a Path) -> Option<&'a Path> {
+    path.strip_prefix(prefix).ok()
+}
+
+/// The final component of the path, if it is a normal file.
+///
+/// If the path terminates in ., .., or consists solely of a root of prefix,
+/// file_name will return None.
+#[cfg(unix)]
+pub fn file_name<'a, P: AsRef<Path> + ?Sized>(
+    path: &'a P,
+) -> Option<&'a OsStr> {
+    use std::os::unix::ffi::OsStrExt;
+
+    let path = path.as_ref().as_os_str().as_bytes();
+    if path.is_empty() {
+        return None;
+    } else if path.len() == 1 && path[0] == b'.' {
+        return None;
+    } else if path.last() == Some(&b'.') {
+        return None;
+    } else if path.len() >= 2 && &path[path.len() - 2..] == &b".."[..] {
+        return None;
+    }
+    let mut last_slash = 0;
+    for (i, &b) in path.iter().enumerate().rev() {
+        if b == b'/' {
+            last_slash = i;
+            break;
+        }
+    }
+    Some(OsStr::from_bytes(&path[last_slash + 1..]))
+}
+
+/// The final component of the path, if it is a normal file.
+///
+/// If the path terminates in ., .., or consists solely of a root of prefix,
+/// file_name will return None.
+#[cfg(not(unix))]
+pub fn file_name<'a, P: AsRef<Path> + ?Sized>(
+    path: &'a P,
+) -> Option<&'a OsStr> {
+    path.as_ref().file_name()
+}