Fix clang compilation error in with_output_tree (follow !1785)
Fix clang compilation error (due to capturing a structured binding name) noticed in !1785 (comment 2997644).
Also fix a warning (due to an unused lambda capture).
cc: @jonrob
Fix clang compilation error (due to capturing a structured binding name) noticed in !1785 (comment 2997644).
Also fix a warning (due to an unused lambda capture).
cc: @jonrob