Merge pull request #10362 from obsidiansystems/maybeLstat

Factor out `nix::maybeLstat`

(cherry-picked from commit 9b88e5284608116b7db0dbd3d5dd7a33b90d52d7)

Change-Id: Id890525e847c890fad6593c594772826ac4d1d50

2 files changed, 19 insertions, 7 deletions

diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 5cd4df8e6..dc724db3e 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -256,16 +256,22 @@ struct stat lstat(const Path & path)
     return st;
 }
 
+std::optional<struct stat> maybeLstat(const Path & path)
+{
+    std::optional<struct stat> st{std::in_place};
+    if (lstat(path.c_str(), &*st))
+    {
+        if (errno == ENOENT || errno == ENOTDIR)
+            st.reset();
+        else
+            throw SysError("getting status of '%s'", path);
+    }
+    return st;
+}
 
 bool pathExists(const Path & path)
 {
-    int res;
-    struct stat st;
-    res = lstat(path.c_str(), &st);
-    if (!res) return true;
-    if (errno != ENOENT && errno != ENOTDIR)
-        throw SysError("getting status of %1%", path);
-    return false;
+    return maybeLstat(path).has_value();
 }
 
 bool pathAccessible(const Path & path)
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index 29a70447e..61df6c4f8 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -115,6 +115,12 @@ struct stat stat(const Path & path);
 struct stat lstat(const Path & path);
 
 /**
+ * `lstat` the given path if it exists.
+ * @return std::nullopt if the path doesn't exist, or an optional containing the result of `lstat` otherwise
+ */
+std::optional<struct stat> maybeLstat(const Path & path);
+
+/**
  * @return true iff the given path exists.
  */
 bool pathExists(const Path & path);