Can't use symbol names as attrset keys

[lucasew]

Describe the bug

Symbol names such as if can't be used as attrset keys

Steps To Reproduce

1. {a.b.if.c = 2; }

Expected behavior
Same as {a.b."if".c = 2; }

nix-env --version output

nix-env (Nix) 2.15.1

Additional context

Sent PR to mitigate the issue to nixpkgs-review: Mic92/nixpkgs-review#344

Priorities

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