diff options
Diffstat (limited to 'compiler/GHC/Unit/Module/Deps.hs')
| -rw-r--r-- | compiler/GHC/Unit/Module/Deps.hs | 137 |
1 files changed, 117 insertions, 20 deletions
diff --git a/compiler/GHC/Unit/Module/Deps.hs b/compiler/GHC/Unit/Module/Deps.hs index 5bdd23239b..2de3fe710d 100644 --- a/compiler/GHC/Unit/Module/Deps.hs +++ b/compiler/GHC/Unit/Module/Deps.hs @@ -17,25 +17,41 @@ import GHC.Utils.Fingerprint import GHC.Utils.Binary -- | Dependency information about ALL modules and packages below this one --- in the import hierarchy. +-- in the import hierarchy. This is the serialisable version of `ImportAvails`. -- -- Invariant: the dependencies of a module @M@ never includes @M@. -- -- Invariant: none of the lists contain duplicates. +-- +-- See Note [Transitive Information in Dependencies] data Dependencies = Deps - { dep_mods :: [ModuleNameWithIsBoot] - -- ^ All home-package modules transitively below this one - -- I.e. modules that this one imports, or that are in the - -- dep_mods of those directly-imported modules - - , dep_pkgs :: [(UnitId, Bool)] - -- ^ All packages transitively below this module - -- I.e. packages to which this module's direct imports belong, - -- or that are in the dep_pkgs of those modules - -- The bool indicates if the package is required to be - -- trusted when the module is imported as a safe import + { dep_direct_mods :: [ModuleNameWithIsBoot] + -- ^ All home-package modules which are directly imported by this one. + + , dep_direct_pkgs :: [UnitId] + -- ^ All packages directly imported by this module + -- I.e. packages to which this module's direct imports belong. + -- + , dep_plgins :: [ModuleName] + -- ^ All the plugins used while compiling this module. + + + -- Transitive information below here + , dep_sig_mods :: ![ModuleName] + -- ^ Transitive closure of hsig files in the home package + + + , dep_trusted_pkgs :: [UnitId] + -- Packages which we are required to trust + -- when the module is imported as a safe import -- (Safe Haskell). See Note [Tracking Trust Transitively] in GHC.Rename.Names + , dep_boot_mods :: [ModuleNameWithIsBoot] + -- ^ All modules which have boot files below this one, and whether we + -- should use the boot file or not. + -- This information is only used to populate the eps_is_boot field. + -- See Note [Structure of dep_boot_mods] + , dep_orphs :: [Module] -- ^ Transitive closure of orphan modules (whether -- home or external pkg). @@ -53,30 +69,39 @@ data Dependencies = Deps -- does NOT include us, unlike 'imp_finsts'. See Note -- [The type family instance consistency story]. - , dep_plgins :: [ModuleName] - -- ^ All the plugins used while compiling this module. } deriving( Eq ) -- Equality used only for old/new comparison in GHC.Iface.Recomp.addFingerprints -- See 'GHC.Tc.Utils.ImportAvails' for details on dependencies. instance Binary Dependencies where - put_ bh deps = do put_ bh (dep_mods deps) - put_ bh (dep_pkgs deps) + put_ bh deps = do put_ bh (dep_direct_mods deps) + put_ bh (dep_direct_pkgs deps) + put_ bh (dep_trusted_pkgs deps) + put_ bh (dep_sig_mods deps) + put_ bh (dep_boot_mods deps) put_ bh (dep_orphs deps) put_ bh (dep_finsts deps) put_ bh (dep_plgins deps) - get bh = do ms <- get bh - ps <- get bh + get bh = do dms <- get bh + dps <- get bh + tps <- get bh + hsigms <- get bh + sms <- get bh os <- get bh fis <- get bh pl <- get bh - return (Deps { dep_mods = ms, dep_pkgs = ps, dep_orphs = os, + return (Deps { dep_direct_mods = dms + , dep_direct_pkgs = dps + , dep_sig_mods = hsigms + , dep_boot_mods = sms + , dep_trusted_pkgs = tps + , dep_orphs = os, dep_finsts = fis, dep_plgins = pl }) noDependencies :: Dependencies -noDependencies = Deps [] [] [] [] [] +noDependencies = Deps [] [] [] [] [] [] [] [] -- | Records modules for which changes may force recompilation of this module -- See wiki: https://gitlab.haskell.org/ghc/ghc/wikis/commentary/compiler/recompilation-avoidance @@ -193,3 +218,75 @@ instance Binary Usage where hash <- get bh return UsageMergedRequirement { usg_mod = mod, usg_mod_hash = hash } i -> error ("Binary.get(Usage): " ++ show i) + + +{- +Note [Transitive Information in Dependencies] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +It is important to be careful what information we put in 'Dependencies' because +ultimately it ends up serialised in an interface file. Interface files must always +be kept up-to-date with the state of the world, so if `Dependencies` needs to be updated +then the module had to be recompiled just to update `Dependencies`. + +Before #16885, the dependencies used to contain the transitive closure of all +home modules. Therefore, if you added an import somewhere low down in the home package +it would recompile nearly every module in your project, just to update this information. + +Now, we are a bit more careful about what we store and +explicitly store transitive information only if it is really needed. + +# Direct Information + +* dep_direct_mods - Directly imported home package modules +* dep_direct_pkgs - Directly imported packages +* dep_plgins - Directly used plugins + +# Transitive Information + +Some features of the compiler require transitive information about what is currently +being compiled, so that is explicitly stored separately in the form they need. + +* dep_trusted_pkgs - Only used for the -fpackage-trust feature +* dep_boot_mods - Only used to populate eps_is_boot in -c mode +* dep_orphs - Modules with orphan instances +* dep_finsts - Modules with type family instances + +Important note: If you add some transitive information to the interface file then +you need to make sure recompilation is triggered when it could be out of date. +The correct way to do this is to include the transitive information in the export +hash of the module. The export hash is computed in `GHC.Iface.Recomp.addFingerprints`. +-} + +{- +Note [Structure of mod_boot_deps] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +In `-c` mode we always need to know whether to load the normal or boot version of +an interface file, and this can't be determined from just looking at the direct imports. + +Consider modules with dependencies: + +``` +A -(S)-> B +A -> C -> B -(S)-> B +``` + +Say when compiling module `A` that we need to load the interface for `B`, do we load +`B.hi` or `B.hi-boot`? Well, `A` does directly {-# SOURCE #-} import B, so you might think +that we would load the `B.hi-boot` file, however this is wrong because `C` imports +`B` normally. Therefore in the interface file for `C` we still need to record that +there is a hs-boot file for `B` below it but that we now want `B.hi` rather than +`B.hi-boot`. When `C` is imported, the fact that it needs `B.hi` clobbers the `{- SOURCE -}` +import for `B`. + +Therefore in mod_boot_deps we store the names of any modules which have hs-boot files, +and whether we want to import the .hi or .hi-boot version of the interface file. + +If you get this wrong, then GHC fails to compile, so there is a test but you might +not make it that far if you get this wrong! + +Question: does this happen even across packages? +No: if I need to load the interface for module X from package P I always look for p:X.hi. + +-} |