rustc: Add a realpath utility function

This is required in rustc to resolve symlinks for utilities such as the sysroot
and the rpath values which are encoded into binaries.

src/librustc/lib.rs

@@ -127,6 +127,7 @@ pub mod util {
     pub mod ppaux;
     pub mod sha2;
     pub mod nodemap;
+    pub mod fs;
 }
 
 pub mod lib {

src/librustc/util/fs.rs

@@ -0,0 +1,103 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::io;
+use std::io::fs;
+use std::os;
+
+/// Returns an absolute path in the filesystem that `path` points to. The
+/// returned path does not contain any symlinks in its hierarchy.
+pub fn realpath(original: &Path) -> io::IoResult<Path> {
+    static MAX_LINKS_FOLLOWED: uint = 256;
+    let original = os::make_absolute(original);
+
+    // Right now lstat on windows doesn't work quite well
+    if cfg!(windows) {
+        return Ok(original)
+    }
+
+    let result = original.root_path();
+    let mut result = result.expect("make_absolute has no root_path");
+    let mut followed = 0;
+
+    for part in original.components() {
+        result.push(part);
+
+        loop {
+            if followed == MAX_LINKS_FOLLOWED {
+                return Err(io::standard_error(io::InvalidInput))
+            }
+
+            match fs::lstat(&result) {
+                Err(..) => break,
+                Ok(ref stat) if stat.kind != io::TypeSymlink => break,
+                Ok(..) => {
+                    followed += 1;
+                    let path = try!(fs::readlink(&result));
+                    result.pop();
+                    result.push(path);
+                }
+            }
+        }
+    }
+
+    return Ok(result);
+}
+
+#[cfg(not(windows), test)]
+mod test {
+    use std::io;
+    use std::io::fs::{File, symlink, mkdir, mkdir_recursive};
+    use super::realpath;
+    use std::io::TempDir;
+
+    #[test]
+    fn realpath_works() {
+        let tmpdir = TempDir::new("rustc-fs").unwrap();
+        let tmpdir = realpath(tmpdir.path()).unwrap();
+        let file = tmpdir.join("test");
+        let dir = tmpdir.join("test2");
+        let link = dir.join("link");
+        let linkdir = tmpdir.join("test3");
+
+        File::create(&file).unwrap();
+        mkdir(&dir, io::UserRWX).unwrap();
+        symlink(&file, &link).unwrap();
+        symlink(&dir, &linkdir).unwrap();
+
+        assert!(realpath(&tmpdir).unwrap() == tmpdir);
+        assert!(realpath(&file).unwrap() == file);
+        assert!(realpath(&link).unwrap() == file);
+        assert!(realpath(&linkdir).unwrap() == dir);
+        assert!(realpath(&linkdir.join("link")).unwrap() == file);
+    }
+
+    #[test]
+    fn realpath_works_tricky() {
+        let tmpdir = TempDir::new("rustc-fs").unwrap();
+        let tmpdir = realpath(tmpdir.path()).unwrap();
+
+        let a = tmpdir.join("a");
+        let b = a.join("b");
+        let c = b.join("c");
+        let d = a.join("d");
+        let e = d.join("e");
+        let f = a.join("f");
+
+        mkdir_recursive(&b, io::UserRWX).unwrap();
+        mkdir_recursive(&d, io::UserRWX).unwrap();
+        File::create(&f).unwrap();
+        symlink(&Path::new("../d/e"), &c).unwrap();
+        symlink(&Path::new("../f"), &e).unwrap();
+
+        assert!(realpath(&c).unwrap() == f);
+        assert!(realpath(&e).unwrap() == f);
+    }
+}