1 files changed, 109 insertions, 0 deletions
diff --git a/src/bootstrap/util.rs b/src/bootstrap/util.rs
index 8e770d4d57f..30d9665dd0f 100644
--- a/src/bootstrap/util.rs
+++ b/src/bootstrap/util.rs
@@ -440,3 +440,112 @@ fn fail(s: &str) -> ! {
     println!("\n\n{}\n\n", s);
     std::process::exit(1);
 }
+
+/// Copied from `std::path::absolute` until it stabilizes.
+///
+/// FIXME: this shouldn't exist.
+pub(crate) fn absolute(path: &Path) -> PathBuf {
+    if path.as_os_str().is_empty() {
+        panic!("can't make empty path absolute");
+    }
+    #[cfg(unix)]
+    {
+        t!(absolute_unix(path), format!("could not make path absolute: {}", path.display()))
+    }
+    #[cfg(windows)]
+    {
+        t!(absolute_windows(path), format!("could not make path absolute: {}", path.display()))
+    }
+    #[cfg(not(any(unix, windows)))]
+    {
+        println!("warning: bootstrap is not supported on non-unix platforms");
+        t!(std::fs::canonicalize(t!(std::env::current_dir()))).join(path)
+    }
+}
+
+#[cfg(unix)]
+/// Make a POSIX path absolute without changing its semantics.
+fn absolute_unix(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
+
+    use std::os::unix::prelude::OsStrExt;
+    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)
+}
+
+#[cfg(windows)]
+fn absolute_windows(path: &std::path::Path) -> std::io::Result<std::path::PathBuf> {
+    use std::ffi::OsString;
+    use std::io::Error;
+    use std::os::windows::ffi::{OsStrExt, OsStringExt};
+    use std::ptr::null_mut;
+    #[link(name = "kernel32")]
+    extern "system" {
+        fn GetFullPathNameW(
+            lpFileName: *const u16,
+            nBufferLength: u32,
+            lpBuffer: *mut u16,
+            lpFilePart: *mut *const u16,
+        ) -> u32;
+    }
+
+    unsafe {
+        // encode the path as UTF-16
+        let path: Vec<u16> = path.as_os_str().encode_wide().chain([0]).collect();
+        let mut buffer = Vec::new();
+        // Loop until either success or failure.
+        loop {
+            // Try to get the absolute path
+            let len = GetFullPathNameW(
+                path.as_ptr(),
+                buffer.len().try_into().unwrap(),
+                buffer.as_mut_ptr(),
+                null_mut(),
+            );
+            match len as usize {
+                // Failure
+                0 => return Err(Error::last_os_error()),
+                // Buffer is too small, resize.
+                len if len > buffer.len() => buffer.resize(len, 0),
+                // Success!
+                len => {
+                    buffer.truncate(len);
+                    return Ok(OsString::from_wide(&buffer).into());
+                }
+            }
+        }
+    }
+}