builtins.readDir: fix nix error trace on filesystem errors

[Mic92]

Motivation

builtins.readDir: fix nix error trace on filesystem errors

Before:

nix-env % ./src/nix/nix eval --impure --expr 'let f = builtins.readDir "/nix/store/39z5zpb72qrnxl832nwphcd4ihfhix3j-hello-2.12.1/foobar"; in f' --show-trace                                           
error: filesystem error: directory iterator cannot open directory: No such file or directory [/nix/store/39z5zpb72qrnxl832nwphcd4ihfhix3j-hello-2.12.1/foobar]                                         

After:

error:                                                                                                                                                                                                 
       … while calling the 'readDir' builtin                                                                                                                                                           
         at «string»:1:9:                                                                                                                                                                              
            1| let f = builtins.readDir "/nix/store/39z5zpb72qrnxl832nwphcd4ihfhix3j-hello-2.12.1/foobar"; in f                                                                                        
             |         ^                                                                                                                                                                               
                                                                                                                                                                                                       
       error: reading directory content failed: filesystem error: directory iterator cannot open directory: No such file or directory [/nix/store/39z5zpb72qrnxl832nwphcd4ihfhix3j-hello-2.12.1/foobar]

Context

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[Mic92]

There are sure more errors like this in here. I see for example a few "fs::is_$type", which can also throw errors.

[Mic92]

Now that @Ericson2314 is mentioning it the SysError one might actually not be the right one to use for rethrowing

[Mic92]

This is now mergeable.

[Ericson2314]

I would convert to a nix exception in PosixSourceAccessor::readDirectory, and then make the catch-rethrow in the evaluator just add the position info.

We want all SourceAccessors to throw the same sorts of exceptions, I think.

[roberth]

@mergifyio rebase

[mergify[bot]]

rebase

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[roberth]

@mergify rebase

[mergify[bot]]

rebase

✅ Branch has been successfully rebased

[Mic92]

@Ericson2314 ok. This is better. I also fixed a similar issue in :lf, which would make the repl crash.

[Mic92]

Fixed following the suggestions of @Ericson2314 and also fixed a similar repl crash.

[Mic92]

@Ericson2314 applied

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/nix-2-25-released/55994/1