“warning” text in nix flake show output on ommiting legacyPackages disrupts visual structure inordinately

[schuelermine]

Describe the bug

If you run nix flake show on a flake that has legacyPackages, they are omitted, and a warning is emitted to show this.
However, the “warning” text shifts the box drawing characters making up the tree structure to the side, disrupting the entire visual.

Steps To Reproduce

1. Run nix flake show nixpkgs
2. Observe:

$ nix flake show nixpkgs
github:NixOS/nixpkgs/a529f0c125a78343b145a8eb2b915b0295e4f459
├───checks
│   └───x86_64-linux
│       └───tarball: derivation 'nixpkgs-tarball-22.05pre20220131.a529f0c'
├───htmlDocs: unknown
├───legacyPackages
warning: │   ├───aarch64-darwin: omitted (use '--legacy' to show)
warning: │   ├───aarch64-linux: omitted (use '--legacy' to show)
warning: │   ├───armv6l-linux: omitted (use '--legacy' to show)
warning: │   ├───armv7l-linux: omitted (use '--legacy' to show)
warning: │   ├───i686-linux: omitted (use '--legacy' to show)
warning: │   ├───mipsel-linux: omitted (use '--legacy' to show)
warning: │   ├───x86_64-darwin: omitted (use '--legacy' to show)
warning: │   └───x86_64-linux: omitted (use '--legacy' to show)
├───lib: unknown
└───nixosModules
    └───notDetected: NixOS module

Expected behavior

github:NixOS/nixpkgs/a529f0c125a78343b145a8eb2b915b0295e4f459
├───checks
│   └───x86_64-linux
│       └───tarball: derivation 'nixpkgs-tarball-22.05pre20220131.a529f0c'
├───htmlDocs: unknown
├───legacyPackages
│   ├───aarch64-darwin: omitted (use '--legacy' to show)
│   ├───aarch64-linux: omitted (use '--legacy' to show)
│   ├───armv6l-linux: omitted (use '--legacy' to show)
│   ├───armv7l-linux: omitted (use '--legacy' to show)
│   ├───i686-linux: omitted (use '--legacy' to show)
│   ├───mipsel-linux: omitted (use '--legacy' to show)
│   ├───x86_64-darwin: omitted (use '--legacy' to show)
│   └───x86_64-linux: omitted (use '--legacy' to show)
├───lib: unknown
└───nixosModules
    └───notDetected: NixOS module
warning: some outputs not shown because they are legacy packages (use '--legacy' to show)

or similar

nix-env --version output
nix-env (Nix) 2.7.0pre20220124_0a70b37

[edolstra]

Do we actually need the warning? Since it already says use '--legacy' to show.