Revert "Revert "getSourceExpr(): Handle channels" (assert failure)"
Revert "Revert "getSourceExpr(): Handle channels" (assert failure)"

Upstream fixed the issue ("1024 is enough for anyone"), will merge shortly.

This reverts commit 6da14889cd71f2ef64dc43d7ed07010be889a65e.

dtzWill/nix,dtzWill/nix,dtzWill/nix,dtzWill/nix,dtzWill/nix