`std::path::absolute`

7 files changed, 208 insertions, 4 deletions

diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index 4f44a3183a6..f93d64bf5d3 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -222,6 +222,7 @@
 // std is implemented with unstable features, many of which are internal
 // compiler details that will never be stable
 // NB: the following list is sorted to minimize merge conflicts.
+#![feature(absolute_path)]
 #![feature(alloc_error_handler)]
 #![feature(alloc_layout_extra)]
 #![feature(allocator_api)]
diff --git a/library/std/src/path.rs b/library/std/src/path.rs
index 85cad65da6a..dc5922c53ba 100644
--- a/library/std/src/path.rs
+++ b/library/std/src/path.rs
@@ -85,7 +85,7 @@ use crate::str::FromStr;
 use crate::sync::Arc;
 
 use crate::ffi::{OsStr, OsString};
-
+use crate::sys;
 use crate::sys::path::{is_sep_byte, is_verbatim_sep, parse_prefix, MAIN_SEP_STR};
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -3164,3 +3164,79 @@ impl Error for StripPrefixError {
         "prefix not found"
     }
 }
+
+/// Makes the path absolute without accessing the filesystem.
+///
+/// If the path is relative, the current directory is used as the base directory.
+/// All intermediate components will be resolved according to platforms-specific
+/// rules but unlike [`canonicalize`][crate::fs::canonicalize] this does not
+/// resolve symlinks and may succeed even if the path does not exist.
+///
+/// If the `path` is empty or getting the
+/// [current directory][crate::env::current_dir] fails then an error will be
+/// returned.
+///
+/// # Examples
+///
+/// ## Posix paths
+///
+/// ```
+/// #![feature(absolute_path)]
+/// # #[cfg(unix)]
+/// fn main() -> std::io::Result<()> {
+///   use std::path::{self, Path};
+///
+///   // Relative to absolute
+///   let absolute = path::absolute("foo/./bar")?;
+///   assert!(absolute.ends_with("foo/bar"));
+///
+///   // Absolute to absolute
+///   let absolute = path::absolute("/foo//test/.././bar.rs")?;
+///   assert_eq!(absolute, Path::new("/foo/test/../bar.rs"));
+///   Ok(())
+/// }
+/// # #[cfg(not(unix))]
+/// # fn main() {}
+/// ```
+///
+/// The paths is resolved using [POSIX semantics][posix-semantics] except that
+/// it stops short of resolving symlinks. This means it will keep `..`
+/// components and trailing slashes.
+///
+/// ## Windows paths
+///
+/// ```
+/// #![feature(absolute_path)]
+/// # #[cfg(windows)]
+/// fn main() -> std::io::Result<()> {
+///   use std::path::{self, Path};
+///
+///   // Relative to absolute
+///   let absolute = path::absolute("foo/./bar")?;
+///   assert!(absolute.ends_with(r"foo\bar"));
+///
+///   // Absolute to absolute
+///   let absolute = path::absolute(r"C:\foo//test\..\./bar.rs")?;
+///
+///   assert_eq!(absolute, Path::new(r"C:\foo\bar.rs"));
+///   Ok(())
+/// }
+/// # #[cfg(not(windows))]
+/// # fn main() {}
+/// ```
+///
+/// For verbatim paths this will simply return the path as given. For other
+/// paths this is currently equivalent to calling [`GetFullPathNameW`][windows-path]
+/// This may change in the future.
+///
+/// [posix-semantics]: https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13
+/// [windows-path]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-getfullpathnamew
+#[unstable(feature = "absolute_path", issue = "none")]
+pub fn absolute<P: AsRef<Path>>(path: P) -> io::Result<PathBuf> {
+    let path = path.as_ref();
+    if path.as_os_str().is_empty() {
+        Err(io::const_io_error!(io::ErrorKind::InvalidInput, "cannot make an empty path absolute",))
+    } else {
+        sys::path::absolute(path)
+    }
+}
diff --git a/library/std/src/path/tests.rs b/library/std/src/path/tests.rs
index 2bf499e1ab8..cf35254a2e3 100644
--- a/library/std/src/path/tests.rs
+++ b/library/std/src/path/tests.rs
@@ -1665,6 +1665,64 @@ fn test_ord() {
     ord!(Equal, "foo/bar", "foo/bar//");
 }
 
+#[test]
+#[cfg(unix)]
+fn test_unix_absolute() {
+    use crate::path::absolute;
+
+    assert!(absolute("").is_err());
+
+    let relative = "a/b";
+    let mut expected = crate::env::current_dir().unwrap();
+    expected.push(relative);
+    assert_eq!(absolute(relative).unwrap(), expected);
+
+    // Test how components are collected.
+    assert_eq!(absolute("/a/b/c").unwrap(), Path::new("/a/b/c"));
+    assert_eq!(absolute("/a//b/c").unwrap(), Path::new("/a/b/c"));
+    assert_eq!(absolute("//a/b/c").unwrap(), Path::new("//a/b/c"));
+    assert_eq!(absolute("///a/b/c").unwrap(), Path::new("/a/b/c"));
+    assert_eq!(absolute("/a/b/c/").unwrap(), Path::new("/a/b/c/"));
+    assert_eq!(absolute("/a/./b/../c/.././..").unwrap(), Path::new("/a/b/../c/../.."));
+}
+
+#[test]
+#[cfg(windows)]
+fn test_windows_absolute() {
+    use crate::path::absolute;
+    // An empty path is an error.
+    assert!(absolute("").is_err());
+
+    let relative = r"a\b";
+    let mut expected = crate::env::current_dir().unwrap();
+    expected.push(relative);
+    assert_eq!(absolute(relative).unwrap(), expected);
+
+    macro_rules! unchanged(
+        ($path:expr) => {
+            assert_eq!(absolute($path).unwrap(), Path::new($path));
+        }
+    );
+
+    unchanged!(r"C:\path\to\file");
+    unchanged!(r"C:\path\to\file\");
+    unchanged!(r"\\server\share\to\file");
+    unchanged!(r"\\server.\share.\to\file");
+    unchanged!(r"\\.\PIPE\name");
+    unchanged!(r"\\.\C:\path\to\COM1");
+    unchanged!(r"\\?\C:\path\to\file");
+    unchanged!(r"\\?\UNC\server\share\to\file");
+    unchanged!(r"\\?\PIPE\name");
+    // Verbatim paths are always unchanged, no matter what.
+    unchanged!(r"\\?\path.\to/file..");
+
+    assert_eq!(absolute(r"C:\path..\to.\file.").unwrap(), Path::new(r"C:\path..\to\file"));
+    assert_eq!(absolute(r"C:\path\to\COM1").unwrap(), Path::new(r"\\.\COM1"));
+    assert_eq!(absolute(r"C:\path\to\COM1.txt").unwrap(), Path::new(r"\\.\COM1"));
+    assert_eq!(absolute(r"C:\path\to\COM1  .txt").unwrap(), Path::new(r"\\.\COM1"));
+    assert_eq!(absolute(r"C:\path\to\cOnOuT$").unwrap(), Path::new(r"\\.\cOnOuT$"));
+}
+
 #[bench]
 fn bench_path_cmp_fast_path_buf_sort(b: &mut test::Bencher) {
     let prefix = "my/home";
diff --git a/library/std/src/sys/sgx/path.rs b/library/std/src/sys/sgx/path.rs
index 840a7ae0426..9cfc61bf174 100644
--- a/library/std/src/sys/sgx/path.rs
+++ b/library/std/src/sys/sgx/path.rs
@@ -1,5 +1,6 @@
 use crate::ffi::OsStr;
-use crate::path::Prefix;
+use crate::path::{Path, PathBuf, Prefix};
+use crate::sys::unsupported;
 
 #[inline]
 pub fn is_sep_byte(b: u8) -> bool {
@@ -17,3 +18,7 @@ pub fn parse_prefix(_: &OsStr) -> Option<Prefix<'_>> {
 
 pub const MAIN_SEP_STR: &str = "/";
 pub const MAIN_SEP: char = '/';
+
+pub(crate) fn absolute(_path: &Path) -> io::Result<PathBuf> {
+    unsupported()
+}
diff --git a/library/std/src/sys/solid/path.rs b/library/std/src/sys/solid/path.rs
index 4a14332d499..ed532dc989b 100644
--- a/library/std/src/sys/solid/path.rs
+++ b/library/std/src/sys/solid/path.rs
@@ -1,5 +1,6 @@
 use crate::ffi::OsStr;
-use crate::path::Prefix;
+use crate::path::{Path, PathBuf, Prefix};
+use crate::sys::unsupported;
 
 #[inline]
 pub fn is_sep_byte(b: u8) -> bool {
@@ -17,3 +18,7 @@ pub fn parse_prefix(_: &OsStr) -> Option<Prefix<'_>> {
 
 pub const MAIN_SEP_STR: &str = "\\";
 pub const MAIN_SEP: char = '\\';
+
+pub(crate) fn absolute(_path: &Path) -> io::Result<PathBuf> {
+    unsupported()
+}
diff --git a/library/std/src/sys/unix/path.rs b/library/std/src/sys/unix/path.rs
index 717add9ec48..1fdabab4598 100644
--- a/library/std/src/sys/unix/path.rs
+++ b/library/std/src/sys/unix/path.rs
@@ -1,5 +1,8 @@
+use crate::env;
 use crate::ffi::OsStr;
-use crate::path::Prefix;
+use crate::io;
+use crate::os::unix::ffi::OsStrExt;
+use crate::path::{Path, PathBuf, Prefix};
 
 #[inline]
 pub fn is_sep_byte(b: u8) -> bool {
@@ -18,3 +21,43 @@ pub fn parse_prefix(_: &OsStr) -> Option<Prefix<'_>> {
 
 pub const MAIN_SEP_STR: &str = "/";
 pub const MAIN_SEP: char = '/';
+
+/// Make a POSIX path absolute without changing its semantics.
+pub(crate) fn absolute(path: &Path) -> io::Result<PathBuf> {
+    // This is mostly a wrapper around collecting `Path::components`, with
+    // exceptions made where this conflicts with the POSIX specification.
+    // See 4.13 Pathname Resolution, IEEE Std 1003.1-2017
+    // https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13
+
+    let mut components = path.components();
+    let path_os = path.as_os_str().as_bytes();
+
+    let mut normalized = if path.is_absolute() {
+        // "If a pathname begins with two successive <slash> characters, the
+        // first component following the leading <slash> characters may be
+        // interpreted in an implementation-defined manner, although more than
+        // two leading <slash> characters shall be treated as a single <slash>
+        // character."
+        if path_os.starts_with(b"//") && !path_os.starts_with(b"///") {
+            components.next();
+            PathBuf::from("//")
+        } else {
+            PathBuf::new()
+        }
+    } else {
+        env::current_dir()?
+    };
+    normalized.extend(components);
+
+    // "Interfaces using pathname resolution may specify additional constraints
+    // when a pathname that does not name an existing directory contains at
+    // least one non- <slash> character and contains one or more trailing
+    // <slash> characters".
+    // A trailing <slash> is also meaningful if "a symbolic link is
+    // encountered during pathname resolution".
+    if path_os.ends_with(b"/") {
+        normalized.push("");
+    }
+
+    Ok(normalized)
+}
diff --git a/library/std/src/sys/windows/path.rs b/library/std/src/sys/windows/path.rs
index 79e0eaf6c34..e54fcaed495 100644
--- a/library/std/src/sys/windows/path.rs
+++ b/library/std/src/sys/windows/path.rs
@@ -260,3 +260,19 @@ pub(crate) fn maybe_verbatim(path: &Path) -> io::Result<Vec<u16>> {
     )?;
     Ok(path)
 }
+
+/// Make a Windows path absolute.
+pub(crate) fn absolute(path: &Path) -> io::Result<PathBuf> {
+    if path.as_os_str().bytes().starts_with(br"\\?\") {
+        return Ok(path.into());
+    }
+    let path = to_u16s(path)?;
+    let lpfilename = path.as_ptr();
+    fill_utf16_buf(
+        // SAFETY: `fill_utf16_buf` ensures the `buffer` and `size` are valid.
+        // `lpfilename` is a pointer to a null terminated string that is not
+        // invalidated until after `GetFullPathNameW` returns successfully.
+        |buffer, size| unsafe { c::GetFullPathNameW(lpfilename, size, buffer, ptr::null_mut()) },
+        super::os2path,
+    )
+}