Make os::getcwd() return IoResult<Path>

os::getcwd() panics if the current directory is not available. According
to getcwd(3), there are three cases:

- EACCES: Permission denied.
- ENOENT: The current working directory has been removed.
- ERANGE: The buffer size is less than the actual absolute path.

This commit makes os::getcwd() return IoResult<Path>, not just Path,
preventing it from panicking.

As os::make_absolute() depends on os::getcwd(), it is also modified to
return IoResult<Path>.

Fixes #16946.

[breaking-change]

4 files changed, 43 insertions, 30 deletions

diff --git a/src/libstd/io/process.rs b/src/libstd/io/process.rs
index 16e568f30f2..592ec0681a9 100644
--- a/src/libstd/io/process.rs
+++ b/src/libstd/io/process.rs
@@ -974,7 +974,7 @@ mod tests {
         let prog = pwd_cmd().spawn().unwrap();
 
         let output = String::from_utf8(prog.wait_with_output().unwrap().output).unwrap();
-        let parent_dir = os::getcwd();
+        let parent_dir = os::getcwd().unwrap();
         let child_dir = Path::new(output.as_slice().trim());
 
         let parent_stat = parent_dir.stat().unwrap();
@@ -989,7 +989,7 @@ mod tests {
         use os;
         // test changing to the parent of os::getcwd() because we know
         // the path exists (and os::getcwd() is not expected to be root)
-        let parent_dir = os::getcwd().dir_path();
+        let parent_dir = os::getcwd().unwrap().dir_path();
         let prog = pwd_cmd().cwd(&parent_dir).spawn().unwrap();
 
         let output = String::from_utf8(prog.wait_with_output().unwrap().output).unwrap();
diff --git a/src/libstd/io/tempfile.rs b/src/libstd/io/tempfile.rs
index e9d6ef2e341..a232231733d 100644
--- a/src/libstd/io/tempfile.rs
+++ b/src/libstd/io/tempfile.rs
@@ -35,7 +35,8 @@ impl TempDir {
     /// If no directory can be created, `Err` is returned.
     pub fn new_in(tmpdir: &Path, suffix: &str) -> IoResult<TempDir> {
         if !tmpdir.is_absolute() {
-            return TempDir::new_in(&os::make_absolute(tmpdir), suffix);
+            let abs_tmpdir = try!(os::make_absolute(tmpdir));
+            return TempDir::new_in(&abs_tmpdir, suffix);
         }
 
         static CNT: atomic::AtomicUint = atomic::INIT_ATOMIC_UINT;
diff --git a/src/libstd/io/test.rs b/src/libstd/io/test.rs
index 6571dc41585..a153ead2a38 100644
--- a/src/libstd/io/test.rs
+++ b/src/libstd/io/test.rs
@@ -75,7 +75,7 @@ fn base_port() -> u16 {
     ];
 
     // FIXME (#9639): This needs to handle non-utf8 paths
-    let path = os::getcwd();
+    let path = os::getcwd().unwrap();
     let path_s = path.as_str().unwrap();
 
     let mut final_base = base;
diff --git a/src/libstd/os.rs b/src/libstd/os.rs
index f7afce9f409..971138c06fb 100644
--- a/src/libstd/os.rs
+++ b/src/libstd/os.rs
@@ -38,7 +38,7 @@ pub use self::MapError::*;
 use clone::Clone;
 use error::{FromError, Error};
 use fmt;
-use io::IoResult;
+use io::{IoResult, IoError};
 use iter::Iterator;
 use libc::{c_void, c_int};
 use libc;
@@ -76,15 +76,16 @@ pub fn num_cpus() -> uint {
 pub const TMPBUF_SZ : uint = 1000u;
 const BUF_BYTES : uint = 2048u;
 
-/// Returns the current working directory as a Path.
+/// Returns the current working directory as a `Path`.
 ///
-/// # Failure
+/// # Errors
 ///
-/// Fails if the current working directory value is invalid:
+/// Returns an `Err` if the current working directory value is invalid.
 /// Possible cases:
 ///
 /// * Current directory does not exist.
 /// * There are insufficient permissions to access the current directory.
+/// * The internal buffer is not large enough to hold the path.
 ///
 /// # Example
 ///
@@ -92,32 +93,34 @@ const BUF_BYTES : uint = 2048u;
 /// use std::os;
 ///
 /// // We assume that we are in a valid directory like "/home".
-/// let current_working_directory = os::getcwd();
+/// let current_working_directory = os::getcwd().unwrap();
 /// println!("The current directory is {}", current_working_directory.display());
 /// // /home
 /// ```
 #[cfg(unix)]
-pub fn getcwd() -> Path {
+pub fn getcwd() -> IoResult<Path> {
     use c_str::CString;
 
     let mut buf = [0 as c_char, ..BUF_BYTES];
     unsafe {
         if libc::getcwd(buf.as_mut_ptr(), buf.len() as libc::size_t).is_null() {
-            panic!()
+            Err(IoError::last_error())
+        } else {
+            Ok(Path::new(CString::new(buf.as_ptr(), false)))
         }
-        Path::new(CString::new(buf.as_ptr(), false))
     }
 }
 
-/// Returns the current working directory as a Path.
+/// Returns the current working directory as a `Path`.
 ///
-/// # Failure
+/// # Errors
 ///
-/// Fails if the current working directory value is invalid.
-/// Possibles cases:
+/// Returns an `Err` if the current working directory value is invalid.
+/// Possible cases:
 ///
 /// * Current directory does not exist.
 /// * There are insufficient permissions to access the current directory.
+/// * The internal buffer is not large enough to hold the path.
 ///
 /// # Example
 ///
@@ -125,23 +128,31 @@ pub fn getcwd() -> Path {
 /// use std::os;
 ///
 /// // We assume that we are in a valid directory like "C:\\Windows".
-/// let current_working_directory = os::getcwd();
+/// let current_working_directory = os::getcwd().unwrap();
 /// println!("The current directory is {}", current_working_directory.display());
 /// // C:\\Windows
 /// ```
 #[cfg(windows)]
-pub fn getcwd() -> Path {
+pub fn getcwd() -> IoResult<Path> {
     use libc::DWORD;
     use libc::GetCurrentDirectoryW;
+    use io::OtherIoError;
 
     let mut buf = [0 as u16, ..BUF_BYTES];
     unsafe {
         if libc::GetCurrentDirectoryW(buf.len() as DWORD, buf.as_mut_ptr()) == 0 as DWORD {
-            panic!();
+            return Err(IoError::last_error());
         }
     }
-    Path::new(String::from_utf16(::str::truncate_utf16_at_nul(&buf))
-              .expect("GetCurrentDirectoryW returned invalid UTF-16"))
+
+    match String::from_utf16(::str::truncate_utf16_at_nul(&buf)) {
+        Some(ref cwd) => Ok(Path::new(cwd)),
+        None => Err(IoError {
+            kind: OtherIoError,
+            desc: "GetCurrentDirectoryW returned invalid UTF-16",
+            detail: None,
+        }),
+    }
 }
 
 #[cfg(windows)]
@@ -829,20 +840,21 @@ pub fn tmpdir() -> Path {
 ///
 /// // Assume we're in a path like /home/someuser
 /// let rel_path = Path::new("..");
-/// let abs_path = os::make_absolute(&rel_path);
+/// let abs_path = os::make_absolute(&rel_path).unwrap();
 /// println!("The absolute path is {}", abs_path.display());
 /// // Prints "The absolute path is /home"
 /// ```
 // NB: this is here rather than in path because it is a form of environment
 // querying; what it does depends on the process working directory, not just
 // the input paths.
-pub fn make_absolute(p: &Path) -> Path {
+pub fn make_absolute(p: &Path) -> IoResult<Path> {
     if p.is_absolute() {
-        p.clone()
+        Ok(p.clone())
     } else {
-        let mut ret = getcwd();
-        ret.push(p);
-        ret
+        getcwd().map(|mut cwd| {
+            cwd.push(p);
+            cwd
+        })
     }
 }
 
@@ -1881,11 +1893,11 @@ mod tests {
     fn test() {
         assert!((!Path::new("test-path").is_absolute()));
 
-        let cwd = getcwd();
+        let cwd = getcwd().unwrap();
         debug!("Current working directory: {}", cwd.display());
 
-        debug!("{}", make_absolute(&Path::new("test-path")).display());
-        debug!("{}", make_absolute(&Path::new("/usr/bin")).display());
+        debug!("{}", make_absolute(&Path::new("test-path")).unwrap().display());
+        debug!("{}", make_absolute(&Path::new("/usr/bin")).unwrap().display());
     }
 
     #[test]