Have not been able to get this to work using cargoHash directly either; I specify

[dev-dependencies]
rustc-demangle = "=0.1.24"

but unfortunately get

     > error: failed to select a version for the requirement `rustc-demangle = "^0.1.24"` (locked to 0.1.26)
       > candidate versions found which didn't match: 0.1.24

which seems odd, as it's clearly properly locked:

$ rg -A1 rustc-demangle
Cargo.toml
41:rustc-demangle = "=0.1.24"
42-rustc-literal-escaper = "0.0.5"

Cargo.lock
589: "rustc-demangle",
590- "rustc-literal-escaper",
--
601:name = "rustc-demangle"
602-version = "0.1.24"

Unfortunately cargo tree doesn't seem to work with the build-std dependencies (previously noted: https://github.com/rust-lang/wg-cargo-std-aware/issues/61#issuecomment-774570256):

$ cargo +nightly tree -Z build-std=core --target avr-none -i rustc-demangle
rustc-demangle v0.1.24
[dev-dependencies]
└── relay v0.1.0 (/Users/n8henrie/git/attiny85-relay)

Hey folks! I'm trying to get miri to work on Nix Darwin.

I am using rust-overlay for my devShell:

      let
        overlays = [ rust-overlay.overlays.default ];
        pkgs = import nixpkgs { inherit system overlays; };
        llvm = pkgs.llvmPackages_20;
      in
      {
        devShells.default = pkgs.mkShell {
          buildInputs = with pkgs; [
            (rust-bin.selectLatestNightlyWith (
              toolchain:
              toolchain.default.override {
                extensions = [ "rust-src" "miri" "rustc-dev" ];
              }
            ))
            llvm.llvm
            llvm.libllvm
            llvm.clang
            llvm.lld
            pkg-config
            libffi
            libxml2
            nixfmt
          ];

          LLVM_SYS_201_PREFIX = llvm.llvm.dev;
        };

When I execute miri, it seems to believe it can't find cargo-miri:

$ cargo miri run
error: 'cargo-miri' is not installed for the toolchain 'nightly-aarch64-apple-darwin'.
To install, run `rustup component add miri`

I do still see cargo-miri and miri in my Nix store:

ls $(which cargo | xargs dirname)
cargo cargo-miri miri ...(etc)

Anyone got any insight?