Revert "libstore: simplify makeTemp{,Sibling}Path callers"

Revert submission 3850

Reason for revert: caused multiple regressions noticed in https://git.lix.systems/lix-project/lix/issues/975 and https://git.lix.systems/lix-project/lix/issues/966 (suspected).

Root cause analysis has not been done yet and this breaks Lix on Darwin on HEAD.

Reverted changes: /q/submissionid:3850

Change-Id: I410046be0ed84e84d1530748d29383489e36c72c

lix/libstore/build/derivation-goal.cc

@@ -761,7 +761,11 @@ void replaceValidPath(const Path & storePath, const Path & tmpPath)
        we're repairing (say) Glibc, we end up with a broken system. */
     Path oldPath;
     if (pathExists(storePath)) {
-        oldPath = makeTempSiblingPath(storePath);
+        do {
+            oldPath = makeTempSiblingPath(storePath);
+            // store paths are often directories so we can't just unlink() it
+            // let's make sure the path doesn't exist before we try to use it
+        } while (pathExists(oldPath));
         movePath(storePath, oldPath);
     }
 

lix/libstore/gc.cc

@@ -42,6 +42,7 @@ static void makeSymlink(const Path & link, const Path & target)
 
     /* Create the new symlink. */
     Path tempLink = makeTempPath(link);
+    unlink(tempLink.c_str()); // just in case; ignore errors
     createSymlink(target, tempLink);
 
     /* Atomically replace the old one. */
@@ -96,7 +97,7 @@ void LocalStore::createTempRootsFile()
 
     /* Create the temporary roots file for this process. */
     while (true) {
-        auto tmp = makeTempPath(fnTempRoots);
+        auto tmp = makeTempPath(fnTempRoots, ".tmp");
         AutoCloseFD fd{open(tmp.c_str(), O_RDWR | O_CREAT | O_EXCL | O_CLOEXEC, 0600)};
         if (!fd && errno != EEXIST) {
             throw SysError("opening lock file '%1%'", tmp);

lix/libstore/optimise-store.cc

@@ -218,7 +218,8 @@ void LocalStore::optimisePath_(Activity * act, OptimiseStats & stats,
        its timestamp back to 0. */
     MakeReadOnly makeReadOnly(mustToggle ? dirOfPath : "");
 
-    Path tempLink = makeTempPath(config().realStoreDir + "/");
+    Path tempLink = makeTempPath(config().realStoreDir, "/.tmp-link");
+    unlink(tempLink.c_str()); // just in case; ignore errors
 
     if (link(linkPath.c_str(), tempLink.c_str()) == -1) {
         if (errno == EMLINK) {