cherry-pick https://gerrit.lix.systems/c/lix/+/2100

Cherry-pick https://gerrit.lix.systems/c/lix/+/2100

This change fixes a potential concurrency failure when accessing random
which is not thread safe.

Co-authored-by: Lily Ballard <lily@ballards.net>

src/libutil/file-system.cc

@@ -8,12 +8,12 @@
 #include "nix/util/util.hh"
 
 #include <atomic>
+#include <random>
 #include <cerrno>
 #include <climits>
 #include <cstdio>
 #include <cstdlib>
 #include <deque>
-#include <sstream>
 #include <filesystem>
 
 #include <fcntl.h>
@@ -27,10 +27,6 @@
 # include <io.h>
 #endif
 
-#include "nix/util/strings-inline.hh"
-
-#include "util-config-private.hh"
-
 namespace nix {
 
 DirectoryIterator::DirectoryIterator(const std::filesystem::path& p) {
@@ -641,6 +637,13 @@ std::pair<AutoCloseFD, Path> createTempFile(const Path & prefix)
     return {std::move(fd), tmpl};
 }
 
+Path makeTempPath(const Path & root, const Path & suffix)
+{
+    // start the counter at a random value to minimize issues with preexisting temp paths
+    static std::atomic_uint_fast32_t counter(std::random_device{}());
+    return fmt("%1%%2%-%3%-%4%", root, suffix, getpid(), counter.fetch_add(1, std::memory_order_relaxed));
+}
+
 void createSymlink(const Path & target, const Path & link)
 {
     try {

src/libutil/include/nix/util/file-system.hh

@@ -6,8 +6,6 @@
  */
 
 #include "nix/util/types.hh"
-#include "nix/util/error.hh"
-#include "nix/util/logging.hh"
 #include "nix/util/file-descriptor.hh"
 #include "nix/util/file-path.hh"
 
@@ -18,12 +16,8 @@
 #ifdef _WIN32
 # include <windef.h>
 #endif
-#include <signal.h>
 
-#include <atomic>
 #include <functional>
-#include <map>
-#include <sstream>
 #include <optional>
 
 /**
@@ -335,6 +329,14 @@ Path defaultTempDir();
  */
 bool isExecutableFileAmbient(const std::filesystem::path & exe);
 
+/**
+ * Return temporary path constructed by appending a suffix to a root path.
+ *
+ * The constructed path looks like `<root><suffix>-<pid>-<unique>`. To create a
+ * path nested in a directory, provide a suffix starting with `/`.
+ */
+Path makeTempPath(const Path & root, const Path & suffix = ".tmp");
+
 /**
  * Used in various places.
  */

src/libutil/source-accessor.cc

@@ -1,5 +1,5 @@
+#include <atomic>
 #include "nix/util/source-accessor.hh"
-#include "nix/util/archive.hh"
 
 namespace nix {