From ab79438d68dbc79da41fd97b2ffc3238d039b02d Mon Sep 17 00:00:00 2001
From: Niko Matsakis <niko@alum.mit.edu>
Date: Thu, 17 Nov 2016 12:44:46 -0500
Subject: [PATCH] canonicalize base incremental path on windows

This sidesteps problems with long paths because the canonical path
includes the "magic long path prefix" on Windows.
---
 src/librustc_incremental/persist/fs.rs | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/librustc_incremental/persist/fs.rs b/src/librustc_incremental/persist/fs.rs
index 223200957cb7..2572a9c1d78f 100644
--- a/src/librustc_incremental/persist/fs.rs
+++ b/src/librustc_incremental/persist/fs.rs
@@ -201,6 +201,19 @@ pub fn prepare_session_directory(tcx: TyCtxt) -> Result<bool, ()> {
     debug!("crate-dir: {}", crate_dir.display());
     try!(create_dir(tcx.sess, &crate_dir, "crate"));
 
+    // Hack: canonicalize the path *after creating the directory*
+    // because, on windows, long paths can cause problems;
+    // canonicalization inserts this weird prefix that makes windows
+    // tolerate long paths.
+    let crate_dir = match crate_dir.canonicalize() {
+        Ok(v) => v,
+        Err(err) => {
+            tcx.sess.err(&format!("incremental compilation: error canonicalizing path `{}`: {}",
+                                  crate_dir.display(), err));
+            return Err(());
+        }
+    };
+
     let mut source_directories_already_tried = FxHashSet();
 
     loop {