Don't chmod symlink before moving outputs around

Co-authored-by: Théophane Hufschmitt <regnat@users.noreply.github.com>

src/libstore/build.cc

@@ -4101,6 +4101,11 @@ void DerivationGoal::registerOutputs()
                     if (lstat(actualPath.c_str(), &st))
                         throw SysError("getting attributes of path '%1%'", actualPath);
                     mode |= 0200;
+                    /* Try to change the perms, but only if the file isn't a
+                       symlink as symlinks permissions are mostly ignored and
+                       calling `chmod` on it will just forward the call to the
+                       target of the link. */
+                    if (!S_ISLNK(st.st_mode))
                         if (chmod(actualPath.c_str(), mode) == -1)
                             throw SysError("changing mode of '%1%' to %2$o", actualPath, mode);
                 }

tests/content-addressed.nix

@@ -16,11 +16,14 @@ rec {
   };
   rootCA = mkDerivation {
     name = "dependent";
+    outputs = [ "out" "dev" ];
     buildCommand = ''
       echo "building a CA derivation"
       echo "The seed is ${toString seed}"
       mkdir -p $out
       echo ${rootLegacy}/hello > $out/dep
+      # test symlink at root
+      ln -s $out $dev
     '';
     __contentAddressed = true;
     outputHashMode = "recursive";