Improved path handling for imports

[arduano]

Improved path handling for imports

Slightly improved path handling for the import builtin, non-absolute string handling will be fixed in the future.

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• More robust import tests #131
• Propagate current path through the rust code #130
• Improve error handling for toStrict #129
• Propagate ctx around lambdas for access to current file path #128
• -> Improved path handling for imports #127
• Improved "other" error testing with error codename #132

[urbas]

Relative paths aren't supported in import when using strings. Here's an example:

% nix eval --impure --expr 'let flake = builtins.import "./flake.nix"; in flake.description'            
error:
       … while calling the 'import' builtin

         at «string»:1:13:

            1| let flake = builtins.import "./flake.nix"; in flake.description
             |             ^

       … while realising the context of a path

         at «none»:0: (source not available)

       error: string './flake.nix' doesn't represent an absolute path

Maybe throw an error if the path is relative.

[urbas]

Looks great, but I think importing relative paths as strings is not supported by nix, so can you please replace that part of the logic with an error (instead of that TODO)?

[arduano]

Hey yeah sorry for not getting the chance to address these, only got time to address 1 PR on the train before I went afk for a few days, will address in a day or two

[arduano]

By the way does reviewing these feel easier or harder? Than just conventional large PRs

[urbas]

By the way does reviewing these feel easier or harder? Than just conventional large PRs

I'm using plain github to review and it's pretty easy. Thanks for breaking these up! 👍

[urbas]

Nitpick: you move the type exception from line 358 to here and remove the if block above:

Suggested change

	}
	} else {
	const expected = [Path, NixString];
	throw builtinBasicTypeMismatchError("import", pathStrict, expected);
	}

[urbas]

Nitpick: Maybe add a test for this? Feel free to ignore or add in a separate PR.