Language.Nix: improve and test Identifier handling #669
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The representation with Strings is tricky of course since identifiers in Nix are technically byte strings (if you allow quoting). For our purposes, it is practical to assume that all identifiers are ASCII or UTF-8 encoded. With quoting, we can represent any Unicode character except '\0'.
Instead of properties, give some examples that are hopefully clearer. We can keep the properties and actually execute them as part of a test suite.
It doesn't make sense to prescribe some kind of “correct” behavior with NUL bytes, so it's best not to test it.
Currently this is practically > 95% which isn't great. Presumably, the examples for simple identifiers are very short as well.
With this, we can get below 70% generated identifiers that don't need quoting.
This relates to #164, as there are packages like `assert` which clash with Nix keywords. However, this does not actually provide us with a solution since quoting isn't possible in some contexts (e.g. function arguments).
This increases correctness as toNixName is already used to generate the package expression arguments. If toNixName and attr were to diverge, packages would fail to resolve their dependencies correctly. A side effect of this change is that `pPrint attr` only quotes attribute names as needed, resulting in a huge diff for hackage-packages.nix.
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sternenseemann
commented
Sep 12, 2025
| -- 'parseSimpleIdentifier') in isolation, but won't be accepted by Nix because | ||
| -- [keywords](https://nix.dev/manual/nix/2.30/language/identifiers.html#keywords) | ||
| -- take precedence. | ||
| illegalSimpleIdentifiers :: [String] |
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maybe this should be called nixKeywords, though this is less accurate w.r.t. what it means to us…
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