2 files changed, 120 insertions, 0 deletions
diff --git a/compiler/rustc_fs_util/Cargo.toml b/compiler/rustc_fs_util/Cargo.toml
new file mode 100644
index 00000000000..e4414c788a7
--- /dev/null
+++ b/compiler/rustc_fs_util/Cargo.toml
@@ -0,0 +1,5 @@
+[package]
+authors = ["The Rust Project Developers"]
+name = "rustc_fs_util"
+version = "0.0.0"
+edition = "2018"
diff --git a/compiler/rustc_fs_util/src/lib.rs b/compiler/rustc_fs_util/src/lib.rs
new file mode 100644
index 00000000000..289b9f30c3b
--- /dev/null
+++ b/compiler/rustc_fs_util/src/lib.rs
@@ -0,0 +1,115 @@
+use std::ffi::CString;
+use std::fs;
+use std::io;
+use std::path::{Path, PathBuf};
+
+// Unfortunately, on windows, it looks like msvcrt.dll is silently translating
+// verbatim paths under the hood to non-verbatim paths! This manifests itself as
+// gcc looking like it cannot accept paths of the form `\\?\C:\...`, but the
+// real bug seems to lie in msvcrt.dll.
+//
+// Verbatim paths are generally pretty rare, but the implementation of
+// `fs::canonicalize` currently generates paths of this form, meaning that we're
+// going to be passing quite a few of these down to gcc, so we need to deal with
+// this case.
+//
+// For now we just strip the "verbatim prefix" of `\\?\` from the path. This
+// will probably lose information in some cases, but there's not a whole lot
+// more we can do with a buggy msvcrt...
+//
+// For some more information, see this comment:
+//   https://github.com/rust-lang/rust/issues/25505#issuecomment-102876737
+#[cfg(windows)]
+pub fn fix_windows_verbatim_for_gcc(p: &Path) -> PathBuf {
+    use std::ffi::OsString;
+    use std::path;
+    let mut components = p.components();
+    let prefix = match components.next() {
+        Some(path::Component::Prefix(p)) => p,
+        _ => return p.to_path_buf(),
+    };
+    match prefix.kind() {
+        path::Prefix::VerbatimDisk(disk) => {
+            let mut base = OsString::from(format!("{}:", disk as char));
+            base.push(components.as_path());
+            PathBuf::from(base)
+        }
+        path::Prefix::VerbatimUNC(server, share) => {
+            let mut base = OsString::from(r"\\");
+            base.push(server);
+            base.push(r"\");
+            base.push(share);
+            base.push(components.as_path());
+            PathBuf::from(base)
+        }
+        _ => p.to_path_buf(),
+    }
+}
+
+#[cfg(not(windows))]
+pub fn fix_windows_verbatim_for_gcc(p: &Path) -> PathBuf {
+    p.to_path_buf()
+}
+
+pub enum LinkOrCopy {
+    Link,
+    Copy,
+}
+
+/// Copies `p` into `q`, preferring to use hard-linking if possible. If
+/// `q` already exists, it is removed first.
+/// The result indicates which of the two operations has been performed.
+pub fn link_or_copy<P: AsRef<Path>, Q: AsRef<Path>>(p: P, q: Q) -> io::Result<LinkOrCopy> {
+    let p = p.as_ref();
+    let q = q.as_ref();
+    if q.exists() {
+        fs::remove_file(&q)?;
+    }
+
+    match fs::hard_link(p, q) {
+        Ok(()) => Ok(LinkOrCopy::Link),
+        Err(_) => match fs::copy(p, q) {
+            Ok(_) => Ok(LinkOrCopy::Copy),
+            Err(e) => Err(e),
+        },
+    }
+}
+
+#[derive(Debug)]
+pub enum RenameOrCopyRemove {
+    Rename,
+    CopyRemove,
+}
+
+/// Rename `p` into `q`, preferring to use `rename` if possible.
+/// If `rename` fails (rename may fail for reasons such as crossing
+/// filesystem), fallback to copy & remove
+pub fn rename_or_copy_remove<P: AsRef<Path>, Q: AsRef<Path>>(
+    p: P,
+    q: Q,
+) -> io::Result<RenameOrCopyRemove> {
+    let p = p.as_ref();
+    let q = q.as_ref();
+    match fs::rename(p, q) {
+        Ok(()) => Ok(RenameOrCopyRemove::Rename),
+        Err(_) => match fs::copy(p, q) {
+            Ok(_) => {
+                fs::remove_file(p)?;
+                Ok(RenameOrCopyRemove::CopyRemove)
+            }
+            Err(e) => Err(e),
+        },
+    }
+}
+
+#[cfg(unix)]
+pub fn path_to_c_string(p: &Path) -> CString {
+    use std::ffi::OsStr;
+    use std::os::unix::ffi::OsStrExt;
+    let p: &OsStr = p.as_ref();
+    CString::new(p.as_bytes()).unwrap()
+}
+#[cfg(windows)]
+pub fn path_to_c_string(p: &Path) -> CString {
+    CString::new(p.to_str().unwrap()).unwrap()
+}