Magnus pushed to branch wip/hadrian-persistent-flavour at Glasgow Haskell Compiler / GHC

Commits:

4 changed files:

Changes:

  • changelog.d/hadrian-persist-flavour
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    +section: packaging
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    +synopsis: Hadrian now persists the flavour name in the build root. When
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    +  rebuilding, the previously used flavour is automatically restored, removing
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    +  the need to re-specify it on every invocation and avoiding accidental build
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    +  root invalidation.
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    +issues: #20650
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    +mrs: !7017

  • hadrian/doc/flavours.md
    ... ... @@ -3,7 +3,14 @@
    3 3 
     Hadrian supports a few predefined _build flavours_, i.e. collections of build
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     settings that fully define a GHC build (see `src/Flavour.hs`). Users can add their
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     own build flavours if need be, as described
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    -[here](https://gitlab.haskell.org/ghc/ghc/blob/master/hadrian/doc/user-settings.md#build-flavour).
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    +[here](https://gitlab.haskell.org/ghc/ghc/blob/master/hadrian/doc/user-settings.md#build-flavour) or modify existing flavours using the flavour transformers notion seem below.
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    +
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    +The flavour to be used for a build root can be specified on the command-line
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    +via the `--flavour` flag. Moreover, this flavour name is saved in the build
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    +root; future invocations of Hadrian without a `--flavour` flag will default to
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    +the last-used flavour.
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    +
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    +See `Note [Persisting the flavour]` in `hadrian/src/Settings.hs`
    7 14
    8 15 
     ## Arguments
    9 16

  • hadrian/src/Rules.hs
    ... ... @@ -129,6 +129,7 @@ packageRules = do
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    130 130 
     buildRules :: Rules ()
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     buildRules = do
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    +    Settings.flavourFileRules
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         Rules.BinaryDist.bindistRules
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         Rules.Generate.copyRules
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         Rules.Generate.generateRules

  • hadrian/src/Settings.hs
    1 
    +{-# LANGUAGE TupleSections #-}
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    +{-# LANGUAGE TypeFamilies  #-}
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    +
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     module Settings (
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         getExtraArgs, getArgs, getLibraryWays, getRtsWays, flavour, knownPackages,
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         findPackageByName, unsafeFindPackageByName, unsafeFindPackageByPath,
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         isLibrary, stagePackages, getBignumBackend, completeSetting,
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         queryBuildTarget, queryHostTarget,
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         queryBuild, queryHost,
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    -    queryArch, queryOS, queryVendor
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    +    queryArch, queryOS, queryVendor,
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    +    flavourFileRules
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         ) where
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    10 14 
     import CommandLine
    ... ... @@ -58,6 +62,56 @@ hadrianFlavours =
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         , ghcInGhciFlavour, validateFlavour, slowValidateFlavour
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         ]
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    65 
    +{-
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    +Note [Persisting the flavour]
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    +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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    +Passing the flavour on the command-line means the user must consistently pass
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    +the same --flavour flag to all Hadrian invocations on a particular build root.
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    +Forgetting even once can result in a full rebuild of the tree.
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    +
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    +To avoid this we persist the flavour name in the build root itself
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    +(specifically, in `<build root>/flavour`). We refer to this file when looking
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    +up the active flavour, defaulting to it if the user does not specify a flavour
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    +name explicitly.
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    +-}
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    +
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    +-- | Oracle query type for the active flavour name.
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    +-- See Note [Persisting the flavour].
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    +newtype FlavourName = FlavourName ()
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    +    deriving (Binary, Eq, Hashable, NFData, Show)
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    +type instance RuleResult FlavourName = String
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    +
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    +flavourFileRules :: Rules ()
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    +flavourFileRules = do
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    +    root <- buildRootRules
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    +
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    +    -- Cache the flavour name lookup for the whole Shake run.
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    +    -- alwaysRerun ensures the oracle re-executes on every new invocation so
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    +    -- that a changed --flavour flag is never ignored due to a stale cross-run
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    +    -- cache entry (CLI args are not tracked as Shake dependencies).
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    +    -- See Note [Persisting the flavour].
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    +    void $ addOracleCache $ \(FlavourName _) -> do
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    +        alwaysRerun
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    +        let flavourFile = root -/- "flavour"
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    +        cmdFlavour >>= \case
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    +          Just nm -> do
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    +            putBuild $ "Flavour: " ++ nm
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    +            liftIO $ writeFile flavourFile nm
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    +            return nm
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    +          Nothing -> do
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    +            exists <- doesFileExist flavourFile
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    +            if exists
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    +              then do nm <- liftIO $ readFile flavourFile
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    +                      putBuild $ "Flavour: " ++ nm ++ " (cached from last build, override by passing --flavour=... explicitly)"
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    +                      return nm
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    +              else return userDefaultFlavour
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    +
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    +-- | Lookup the requested flavour name, referring to the persistent flavour
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    +-- file saved from the previous Hadrian execution if not specified.
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    +-- The result is cached for the whole Shake run via the 'FlavourName' oracle.
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    +getFlavourName :: Action String
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    +getFlavourName = askOracle (FlavourName ())
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    +
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     -- | This action looks up a flavour with the name given on the
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     --   command line with @--flavour@, defaulting to 'userDefaultFlavour'
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     --   when no explicit @--flavour@ is passed. It then applies any
    ... ... @@ -66,7 +120,7 @@ hadrianFlavours =
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     --   syntax. See Note [Hadrian settings] at the bottom of this file.
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     flavour :: Action Flavour
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     flavour = do
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    -    flavourName <- fromMaybe userDefaultFlavour <$> cmdFlavour
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    +    flavourName <- getFlavourName
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         when ("quickest" `isPrefixOf` flavourName) $
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           fail $ "The `quickest` flavour has been deprecated. Use `quick` instead.\n"
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               ++ "Skip building dynamic libraries with `quick+no_dynamic_libs`\n"

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