Improve handling of `?`-variables #1939

Job	Run time
Stack / Unit Tests	2m 9s
Nix / All Tests (self-hosted, linux, normal, Ubuntu-22.04, x86_64-linux)	8m 30s
Nix / All Tests (MacM1, self-macos-12, aarch64-darwin)	6m 49s
Formatting and Style	20s
Nix / All Tests (macos-12, macos-12, x86_64-darwin)	27m 41s
	45m 29s

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