Auto merge of #35718 - michaelwoerister:incr-comp-dir-locking, r=alexcrichton

Implement synchronization scheme for incr. comp. directory

This PR implements a copy-on-write-based synchronization scheme for the incremental compilation cache directory. For technical details, see the documentation at the beginning of `rustc_incremental/persist/fs.rs`.

The PR contains unit tests for some functions but for testing whether the scheme properly handles races, a more elaborate test setup would be needed. It would probably involve a small tool that allows to manipulate the incremental compilation directory in a controlled way and then letting a compiler instance run against directories in different states. I don't know if it's worth the trouble of adding another test category to `compiletest`, but I'd be happy to do so.

Fixes #32754
Fixes #34957

1 files changed, 5 insertions, 2 deletions

diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index 60a0d8f0b86..228d6ada01d 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -1976,7 +1976,10 @@ actual:\n\
         // runs.
         let incremental_dir = self.incremental_dir();
         if incremental_dir.exists() {
-            fs::remove_dir_all(&incremental_dir).unwrap();
+            // Canonicalizing the path will convert it to the //?/ format
+            // on Windows, which enables paths longer than 260 character
+            let canonicalized = incremental_dir.canonicalize().unwrap();
+            fs::remove_dir_all(canonicalized).unwrap();
         }
         fs::create_dir_all(&incremental_dir).unwrap();
 
@@ -2041,7 +2044,7 @@ actual:\n\
 
     /// Directory where incremental work products are stored.
     fn incremental_dir(&self) -> PathBuf {
-        self.output_base_name().with_extension("incremental")
+        self.output_base_name().with_extension("inc")
     }
 
     fn run_rmake_test(&self) {