From 4ce8a3ed452f06b18a40cffefc37d47c916927a8 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Wed, 23 Sep 2020 21:29:10 +0200
Subject: [PATCH] Hopefully fix EPERM on macOS

---
 src/libstore/build.cc | 72 ++++++++++++++++++++++++-------------------
 1 file changed, 40 insertions(+), 32 deletions(-)

diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index f0820e711..db7dbc17e 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -1675,6 +1675,33 @@ void DerivationGoal::tryLocalBuild() {
 }
 
 
+static void chmod_(const Path & path, mode_t mode)
+{
+    if (chmod(path.c_str(), mode) == -1)
+        throw SysError("setting permissions on '%s'", path);
+}
+
+
+/* Move/rename path 'src' to 'dst'. Temporarily make 'src' writable if
+   it's a directory and we're not root (to be able to update the
+   directory's parent link ".."). */
+static void movePath(const Path & src, const Path & dst)
+{
+    auto st = lstat(src);
+
+    bool changePerm = (geteuid() && S_ISDIR(st.st_mode) && !(st.st_mode & S_IWUSR));
+
+    if (changePerm)
+        chmod_(src, st.st_mode | S_IWUSR);
+
+    if (rename(src.c_str(), dst.c_str()))
+        throw SysError("renaming '%1%' to '%2%'", src, dst);
+
+    if (changePerm)
+        chmod_(dst, st.st_mode);
+}
+
+
 void replaceValidPath(const Path & storePath, const Path & tmpPath)
 {
     /* We can't atomically replace storePath (the original) with
@@ -1683,12 +1710,20 @@ void replaceValidPath(const Path & storePath, const Path & tmpPath)
        we're repairing (say) Glibc, we end up with a broken system. */
     Path oldPath = (format("%1%.old-%2%-%3%") % storePath % getpid() % random()).str();
     if (pathExists(storePath))
-        rename(storePath.c_str(), oldPath.c_str());
-    if (rename(tmpPath.c_str(), storePath.c_str()) == -1) {
-        auto ex = SysError("moving '%s' to '%s'", tmpPath, storePath);
-        rename(oldPath.c_str(), storePath.c_str()); // attempt to recover
-        throw ex;
+        movePath(storePath, oldPath);
+
+    try {
+        movePath(tmpPath, storePath);
+    } catch (...) {
+        try {
+            // attempt to recover
+            movePath(oldPath, storePath);
+        } catch (...) {
+            ignoreException();
+        }
+        throw;
     }
+
     deletePath(oldPath);
 }
 
@@ -2006,13 +2041,6 @@ HookReply DerivationGoal::tryBuildHook()
 }
 
 
-static void chmod_(const Path & path, mode_t mode)
-{
-    if (chmod(path.c_str(), mode) == -1)
-        throw SysError("setting permissions on '%s'", path);
-}
-
-
 int childEntry(void * arg)
 {
     ((DerivationGoal *) arg)->runChild();
@@ -3731,26 +3759,6 @@ void DerivationGoal::runChild()
 }
 
 
-/* Move/rename path 'src' to 'dst'. Temporarily make 'src' writable if
-   it's a directory and we're not root (to be able to update the
-   directory's parent link ".."). */
-static void movePath(const Path & src, const Path & dst)
-{
-    auto st = lstat(src);
-
-    bool changePerm = (geteuid() && S_ISDIR(st.st_mode) && !(st.st_mode & S_IWUSR));
-
-    if (changePerm)
-        chmod_(src, st.st_mode | S_IWUSR);
-
-    if (rename(src.c_str(), dst.c_str()))
-        throw SysError("renaming '%1%' to '%2%'", src, dst);
-
-    if (changePerm)
-        chmod_(dst, st.st_mode);
-}
-
-
 void DerivationGoal::registerOutputs()
 {
     /* When using a build hook, the build hook can register the output