Language.Nix.Identifier: correctly parse and produce escape sequences in strings #681
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This code previously assumed escape sequences in strings work like in Haskell. This is not generally the case. This commit adds a custom implementation of the relevant parsing and rendering logic which even simplifies some things. Escape sequences are a little weird in Nix since only very few things _have_ to be escaped and some things not always, depending on context (i.e. $). I've linked the best reference (the lexer) in the code, but the manual is also helpful: https://nix.dev/manual/nix/2.30/language/string-literals.html
We currently test two things marginally different things: 1. If we produce identifier syntax with quote, we verify that Nix will be able to parse and evaluate it and later produce the same quoted identifier as we do. (This makes sure we don't quote unnecessarily.) 2. If we prettyShow an Identifier, we verify that Nix will be able to parse and evaluate it and that we will be able to parse what Nix pretty prints.
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Language.Nix.Identifierpretty much assumed that quoted identifiers could be rendered usingshowand parsed usingread. This is not the case and resolved in this PR.Additionally, I added some test cases that roundtrip identifiers through
nix-instantiate --evalwhich should catch any remaining or re-introduced problems with the changed code. This cases are skipped ifnix-instantiatecan't be executed which is the case in Haskell-CI. I have some more tests in mind which I'll add in follow up PRs, I think.Haven't tested whether it actually works in a derivation, but I don't see why not.