strings compare equal to paths, and functions compare equal to themselves

[wyattgill9]

Two equality cases diverge from Nix. Both are in src/expr/vm/builtins/equality.zig.

A string compares equal to a path

$ fix eval --expr '"/a" == /a'
true

$ nix-instantiate --eval -E '"/a" == /a'
false

Nix compares types first, so a string is never equal to a path regardless of spelling.

A function compares equal to itself (equality.zig:105)

$ fix eval --expr 'let f = x: x; in f == f'
true

$ nix-instantiate --eval -E 'let f = x: x; in f == f'
false

Nix returns false for any comparison involving a function, including a value against itself — functions are simply never equal. Pointer identity is not part of the language semantics, and code that filters or dedupes a list of functions will behave differently on the two implementations.

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fix 0.3.0 at 1f1a99cf, built -Doptimize=ReleaseSafe with Zig 0.16.0, darwin/aarch64. Reference implementation is Nix 2.34.8.