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Add System.Nix.StorePath, successor to System.Nix.Path.
The new type acknowledges the store root, and is better named. Future work will migrate all dependents and retire the old module.
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name: hnix-store-core
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version: 0.1.0.0
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version: 0.1.1.0
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synopsis: Core effects for interacting with the Nix store.
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description:
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This package contains types and functions needed to describe
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@ -23,10 +23,12 @@ library
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, System.Nix.GC
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, System.Nix.Hash
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, System.Nix.Internal.Hash
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, System.Nix.Internal.StorePath
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, System.Nix.Nar
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, System.Nix.Path
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, System.Nix.ReadonlyStore
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, System.Nix.Store
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, System.Nix.StorePath
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, System.Nix.Util
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build-depends: base >=4.10 && <5
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, base16-bytestring
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141
hnix-store-core/src/System/Nix/Internal/StorePath.hs
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141
hnix-store-core/src/System/Nix/Internal/StorePath.hs
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{-|
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Description : Representation of Nix store paths.
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-}
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{-# LANGUAGE DataKinds #-}
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{-# LANGUAGE OverloadedStrings #-}
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{-# LANGUAGE KindSignatures #-}
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{-# LANGUAGE ConstraintKinds #-}
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{-# LANGUAGE RecordWildCards #-}
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module System.Nix.Internal.StorePath where
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import System.Nix.Hash (HashAlgorithm(Truncated, SHA256), Digest, encodeBase32)
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import Text.Regex.Base.RegexLike (makeRegex, matchTest)
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import Text.Regex.TDFA.Text (Regex)
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import Data.Text (Text)
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import Data.Text.Encoding (encodeUtf8)
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import GHC.TypeLits (Symbol, KnownSymbol, symbolVal)
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import Data.ByteString (ByteString)
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import qualified Data.ByteString as BS
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import qualified Data.ByteString.Char8 as BC
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-- | A path in a Nix store.
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--
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-- From the Nix thesis: A store path is the full path of a store
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-- object. It has the following anatomy: storeDir/hashPart-name.
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--
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-- @storeDir@: The root of the Nix store (e.g. \/nix\/store).
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--
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-- See the 'StoreDir' haddocks for details on why we represent this at
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-- the type level.
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data StorePath (storeDir :: StoreDir) = StorePath
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{ -- | The 160-bit hash digest reflecting the "address" of the name.
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-- Currently, this is a truncated SHA256 hash.
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storePathHash :: !(Digest StorePathHashAlgo)
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, -- | The (typically human readable) name of the path. For packages
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-- this is typically the package name and version (e.g.
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-- hello-1.2.3).
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storePathName :: !StorePathName
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}
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-- | The name portion of a Nix path.
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--
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-- 'unStorePathName' must only contain a-zA-Z0-9+._?=-, can't start
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-- with a -, and must have at least one character (i.e. it must match
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-- 'storePathNameRegex').
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newtype StorePathName = StorePathName
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{ -- | Extract the contents of the name.
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unStorePathName :: Text
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}
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-- | The hash algorithm used for store path hashes.
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type StorePathHashAlgo = 'Truncated 20 'SHA256
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-- | A type-level representation of the root directory of a Nix store.
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--
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-- The extra complexity of type indices requires justification.
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-- Fundamentally, this boils down to the fact that there is little
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-- meaningful sense in which 'StorePath's rooted at different
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-- directories are of the same type, i.e. there are few if any
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-- non-trivial non-contrived functions or data types that could
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-- equally well accept 'StorePath's from different stores. In current
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-- practice, any real application dealing with Nix stores (including,
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-- in particular, the Nix expression language) only operates over one
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-- store root and only cares about 'StorePath's belonging to that
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-- root. One could imagine a use case that cares about multiple store
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-- roots at once (e.g. the normal \/nix\/store along with some private
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-- store at \/root\/nix\/store to contain secrets), but in that case
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-- distinguishing 'StorePath's that belong to one store or the other
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-- is even /more/ critical: Most operations will only be correct over
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-- one of the stores or another, and it would be an error to mix and
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-- match (e.g. a 'StorePath' in one store could not legitimately refer
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-- to one in another).
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--
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-- As of @5886bc5996537fbf00d1fcfbb29595b8ccc9743e@, the C++ Nix
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-- codebase contains 30 separate places where we assert that a given
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-- store dir is, in fact, in the store we care about; those run-time
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-- assertions could be completely removed if we had stronger types
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-- there. Moreover, there are dozens of other cases where input coming
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-- from the user, from serializations, etc. is parsed and then
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-- required to be in the appropriate store; this case is the
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-- equivalent of an existentially quantified version of 'StorePath'
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-- and, notably, requiring at runtime that the index matches the
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-- ambient store directory we're working in. In every case where a
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-- path is treated as a store path, there is exactly one legitimate
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-- candidate for the store directory it belongs to.
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--
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-- It may be instructive to consider the example of "chroot stores".
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-- Since Nix 2.0, it has been possible to have a store actually live
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-- at one directory (say, $HOME\/nix\/store) with a different
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-- effective store directory (say, \/nix\/store). Nix can build into
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-- a chroot store by running the builds in a mount namespace where the
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-- store is at the effective store directory, can download from a
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-- binary cache containing paths for the effective store directory,
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-- and can run programs in the store that expect to be living at the
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-- effective store directory (via nix run). When viewed as store paths
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-- (rather than random files in the filesystem), paths in a chroot
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-- store have nothing in common with paths in a non-chroot store that
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-- lives in the same directory, and a lot in common with paths in a
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-- non-chroot store that lives in the effective store directory of the
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-- store in question. Store paths in stores with the same effective
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-- store directory share the same hashing scheme, can be copied
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-- between each other, etc. Store paths in stores with different
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-- effective store directories have no relationship to each other that
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-- they don't have to arbitrary other files.
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type StoreDir = Symbol
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-- | Smart constructor for 'StorePathName' that ensures the underlying
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-- content invariant is met.
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makeStorePathName :: Text -> Maybe StorePathName
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makeStorePathName n = case matchTest storePathNameRegex n of
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True -> Just $ StorePathName n
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False -> Nothing
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-- | Regular expression to match valid store path names.
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storePathNameRegex :: Regex
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storePathNameRegex = makeRegex r
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where
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r :: String
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r = "[a-zA-Z0-9\\+\\-\\_\\?\\=][a-zA-Z0-9\\+\\-\\.\\_\\?\\=]*"
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-- | Copied from @RawFilePath@ in the @unix@ package, duplicated here
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-- to avoid the dependency.
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type RawFilePath = ByteString
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-- | Render a 'StorePath' as a 'RawFilePath'.
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storePathToRawFilePath
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:: (KnownStoreDir storeDir)
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=> StorePath storeDir
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-> RawFilePath
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storePathToRawFilePath s@(StorePath {..}) = BS.concat
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[ root
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, "/"
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, hashPart
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, "-"
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, name
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]
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where
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root = BC.pack $ symbolVal s
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hashPart = encodeUtf8 $ encodeBase32 storePathHash
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name = encodeUtf8 $ unStorePathName storePathName
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-- | A 'StoreDir' whose value is known at compile time.
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type KnownStoreDir = KnownSymbol
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19
hnix-store-core/src/System/Nix/StorePath.hs
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19
hnix-store-core/src/System/Nix/StorePath.hs
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{-|
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Description : Representation of Nix store paths.
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-}
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module System.Nix.StorePath
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( -- * Basic store path types
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StorePath(..)
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, StorePathName
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, StorePathHashAlgo
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, StoreDir
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, -- * Manipulating 'StorePathName'
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makeStorePathName
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, unStorePathName
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, storePathNameRegex
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, -- * Rendering out 'StorePath's
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storePathToRawFilePath
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, KnownStoreDir
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) where
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import System.Nix.Internal.StorePath
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