rustc: Don't ICE if we invalidate an invalid incr dir

This showed up on the Windows bot for testing this PR, and this pr allows
`mark_incr_comp_session_as_invalid` ok if it's already invalid, hopefully
avoiding scary ICEs and instead leaving the nicely printed errors

diff --git a/src/librustc/session/mod.rs b/src/librustc/session/mod.rs
index 54bcc64d0685d70ac7d99338c9cd43811698b4e4..19fbbe10be9e079b833e17bdc749f5bd5ce364c1 100644 (file)
--- a/src/librustc/session/mod.rs
+++ b/src/librustc/session/mod.rs
@@ -642,6 +642,7 @@ pub fn mark_incr_comp_session_as_invalid(&self) {
             IncrCompSession::Active { ref session_directory, .. } => {
                 session_directory.clone()
             }
+            IncrCompSession::InvalidBecauseOfErrors { .. } => return,
             _ => bug!("Trying to invalidate IncrCompSession `{:?}`",
                       *incr_comp_session),
         };