Fix regression in passAsFile

Caused by 8063fc497ab78fa72962b93874fe25dcca2b55ed. If tmpDir !=
tmpDirInSandbox (typically when there are multiple concurrent builds
with the same name), the *Path attribute would not point to an
existing file. This caused Nixpkgs' writeTextFile to write an empty
file. In particular this showed up as hanging VM builds (because it
would run an empty run-nixos-vm script and then wait for it to finish
booting).

1 files changed, 3 insertions, 2 deletions

diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 0fd958846440..e00a07d3b1a0 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -1778,10 +1778,11 @@ void DerivationGoal::startBuilder()
         if (passAsFile.find(i.first) == passAsFile.end()) {
             env[i.first] = i.second;
         } else {
-            Path p = tmpDir + "/.attr-" + std::to_string(fileNr++);
+            string fn = ".attr-" + std::to_string(fileNr++);
+            Path p = tmpDir + "/" + fn;
             writeFile(p, i.second);
             filesToChown.insert(p);
-            env[i.first + "Path"] = p;
+            env[i.first + "Path"] = tmpDirInSandbox + "/" + fn;
         }
     }