Change std::io::FilePermission to a typesafe representation

This patch changes `std::io::FilePermissions` from an exposed `u32`
representation to a typesafe representation (that only allows valid
flag combinations) using the `std::bitflags`, thus ensuring a greater
degree of safety on the Rust side.

Despite the change to the type, most code should continue to work
as-is, sincde the new type provides bit operations in the style of C
flags. To get at the underlying integer representation, use the `bits`
method; to (unsafely) convert to `FilePermissions`, use
`FilePermissions::from_bits`.

Closes #6085.

[breaking-change]

2 files changed, 41 insertions, 36 deletions

diff --git a/src/libstd/io/fs.rs b/src/libstd/io/fs.rs
index cd304250b19..6d48b9eee35 100644
--- a/src/libstd/io/fs.rs
+++ b/src/libstd/io/fs.rs
@@ -1119,7 +1119,7 @@ mod test {
         check!(File::create(&input));
         check!(chmod(&input, io::UserRead));
         check!(copy(&input, &out));
-        assert!(check!(out.stat()).perm & io::UserWrite == 0);
+        assert!(!check!(out.stat()).perm.intersects(io::UserWrite));
 
         check!(chmod(&input, io::UserFile));
         check!(chmod(&out, io::UserFile));
@@ -1193,9 +1193,9 @@ mod test {
         let file = tmpdir.join("in.txt");
 
         check!(File::create(&file));
-        assert!(check!(stat(&file)).perm & io::UserWrite == io::UserWrite);
+        assert!(check!(stat(&file)).perm.contains(io::UserWrite));
         check!(chmod(&file, io::UserRead));
-        assert!(check!(stat(&file)).perm & io::UserWrite == 0);
+        assert!(!check!(stat(&file)).perm.contains(io::UserWrite));
 
         match chmod(&tmpdir.join("foo"), io::UserRWX) {
             Ok(..) => fail!("wanted a failure"),
diff --git a/src/libstd/io/mod.rs b/src/libstd/io/mod.rs
index d948738ac56..ff276d02028 100644
--- a/src/libstd/io/mod.rs
+++ b/src/libstd/io/mod.rs
@@ -224,6 +224,7 @@ use fmt;
 use int;
 use iter::Iterator;
 use libc;
+use ops::{BitOr, BitAnd, Sub};
 use os;
 use option::{Option, Some, None};
 use path::Path;
@@ -1558,36 +1559,40 @@ pub struct UnstableFileStat {
     pub gen: u64,
 }
 
-/// A set of permissions for a file or directory is represented by a set of
-/// flags which are or'd together.
-pub type FilePermission = u32;
-
-// Each permission bit
-pub static UserRead: FilePermission     = 0x100;
-pub static UserWrite: FilePermission    = 0x080;
-pub static UserExecute: FilePermission  = 0x040;
-pub static GroupRead: FilePermission    = 0x020;
-pub static GroupWrite: FilePermission   = 0x010;
-pub static GroupExecute: FilePermission = 0x008;
-pub static OtherRead: FilePermission    = 0x004;
-pub static OtherWrite: FilePermission   = 0x002;
-pub static OtherExecute: FilePermission = 0x001;
-
-// Common combinations of these bits
-pub static UserRWX: FilePermission  = UserRead | UserWrite | UserExecute;
-pub static GroupRWX: FilePermission = GroupRead | GroupWrite | GroupExecute;
-pub static OtherRWX: FilePermission = OtherRead | OtherWrite | OtherExecute;
-
-/// A set of permissions for user owned files, this is equivalent to 0644 on
-/// unix-like systems.
-pub static UserFile: FilePermission = UserRead | UserWrite | GroupRead | OtherRead;
-/// A set of permissions for user owned directories, this is equivalent to 0755
-/// on unix-like systems.
-pub static UserDir: FilePermission = UserRWX | GroupRead | GroupExecute |
-                                     OtherRead | OtherExecute;
-/// A set of permissions for user owned executables, this is equivalent to 0755
-/// on unix-like systems.
-pub static UserExec: FilePermission = UserDir;
-
-/// A mask for all possible permission bits
-pub static AllPermissions: FilePermission = 0x1ff;
+bitflags!(
+    #[doc="A set of permissions for a file or directory is represented
+by a set of flags which are or'd together."]
+    #[deriving(Hash)]
+    #[deriving(Show)]
+    flags FilePermission: u32 {
+        static UserRead     = 0o400,
+        static UserWrite    = 0o200,
+        static UserExecute  = 0o100,
+        static GroupRead    = 0o040,
+        static GroupWrite   = 0o020,
+        static GroupExecute = 0o010,
+        static OtherRead    = 0o004,
+        static OtherWrite   = 0o002,
+        static OtherExecute = 0o001,
+
+        static UserRWX  = UserRead.bits | UserWrite.bits | UserExecute.bits,
+        static GroupRWX = GroupRead.bits | GroupWrite.bits | GroupExecute.bits,
+        static OtherRWX = OtherRead.bits | OtherWrite.bits | OtherExecute.bits,
+
+        #[doc="Permissions for user owned files, equivalent to 0644 on
+unix-like systems."]
+        static UserFile = UserRead.bits | UserWrite.bits | GroupRead.bits | OtherRead.bits,
+
+        #[doc="Permissions for user owned directories, equivalent to 0755 on
+unix-like systems."]
+        static UserDir  = UserRWX.bits | GroupRead.bits | GroupExecute.bits |
+                   OtherRead.bits | OtherExecute.bits,
+
+        #[doc="Permissions for user owned executables, equivalent to 0755
+on unix-like systems."]
+        static UserExec = UserDir.bits,
+
+        #[doc="All possible permissions enabled."]
+        static AllPermissions = UserRWX.bits | GroupRWX.bits | OtherRWX.bits
+    }
+)