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Use FastString to store filepaths in interface files, as this data is
highly redundant so we want to share all instances of filepaths in the
compiler session.
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SourceText is serialized along with INLINE pragmas into interface files. Many of
these SourceTexts are identical, for example "{-# INLINE#". When deserialized,
each such SourceText was previously expanded out into a [Char], which is highly
wasteful of memory, and each such instance of the text would allocate an
independent list with its contents as deserializing breaks any sharing that might
have existed.
Instead, we use a `FastString` to represent these, so that each instance unique
text will be interned and stored in a memory efficient manner.
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This will allow to make command line parsing to depend on
diagnostic system (which depends on dynflags)
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This patch moves the field-based logic for disambiguating record updates
to the renamer. The type-directed logic, scheduled for removal, remains
in the typechecker.
To do this properly (and fix the myriad of bugs surrounding the treatment
of duplicate record fields), we took the following main steps:
1. Create GREInfo, a renamer-level equivalent to TyThing which stores
information pertinent to the renamer.
This allows us to uniformly treat imported and local Names in the
renamer, as described in Note [GREInfo].
2. Remove GreName. Instead of a GlobalRdrElt storing GreNames, which
distinguished between normal names and field names, we now store
simple Names in GlobalRdrElt, along with the new GREInfo information
which allows us to recover the FieldLabel for record fields.
3. Add namespacing for record fields, within the OccNames themselves.
This allows us to remove the mangling of duplicate field selectors.
This change ensures we don't print mangled names to the user in
error messages, and allows us to handle duplicate record fields
in Template Haskell.
4. Move record disambiguation to the renamer, and operate on the
level of data constructors instead, to handle #21443.
The error message text for ambiguous record updates has also been
changed to reflect that type-directed disambiguation is on the way
out.
(3) means that OccEnv is now a bit more complex: we first key on the
textual name, which gives an inner map keyed on NameSpace:
OccEnv a ~ FastStringEnv (UniqFM NameSpace a)
Note that this change, along with (2), both increase the memory residency
of GlobalRdrEnv = OccEnv [GlobalRdrElt], which causes a few tests to
regress somewhat in compile-time allocation.
Even though (3) simplified a lot of code (in particular the treatment of
field selectors within Template Haskell and in error messages), it came
with one important wrinkle: in the situation of
-- M.hs-boot
module M where { data A; foo :: A -> Int }
-- M.hs
module M where { data A = MkA { foo :: Int } }
we have that M.hs-boot exports a variable foo, which is supposed to match
with the record field foo that M exports. To solve this issue, we add a
new impedance-matching binding to M
foo{var} = foo{fld}
This mimics the logic that existed already for impedance-binding DFunIds,
but getting it right was a bit tricky.
See Note [Record field impedance matching] in GHC.Tc.Module.
We also needed to be careful to avoid introducing space leaks in GHCi.
So we dehydrate the GlobalRdrEnv before storing it anywhere, e.g. in
ModIface. This means stubbing out all the GREInfo fields, with the
function forceGlobalRdrEnv.
When we read it back in, we rehydrate with rehydrateGlobalRdrEnv.
This robustly avoids any space leaks caused by retaining old type
environments.
Fixes #13352 #14848 #17381 #17551 #19664 #21443 #21444 #21720 #21898 #21946 #21959 #22125 #22160 #23010 #23062 #23063
Updates haddock submodule
-------------------------
Metric Increase:
MultiComponentModules
MultiLayerModules
MultiLayerModulesDefsGhci
MultiLayerModulesNoCode
T13701
T14697
hard_hole_fits
-------------------------
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Closes #17209. This implements GHC Proposal 541, allowing a WARNING
pragma to be annotated with a category like so:
{-# WARNING in "x-partial" head "This function is undefined on empty lists." #-}
The user can then enable, disable and set the severity of such warnings
using command-line flags `-Wx-partial`, `-Werror=x-partial` and so on. There
is a new warning group `-Wextended-warnings` containing all these warnings.
Warnings without a category are treated as if the category was `deprecations`,
and are (still) controlled by the flags `-Wdeprecations`
and `-Wwarnings-deprecations`.
Updates Haddock submodule.
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instances
This is a minor refactor that makes it easy to add and remove fields from
`ModIface_` and `ModIfaceBackend`.
Also change the formatting to make it clear exactly which fields are
fully forced with `rnf`
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Towards #22530
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Create and use moduleGraphModulesBelow in GHC.Unit.Module.Graph that
doesn't need anything from the driver to be used.
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This is helpful when debugging multiple component issues.
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The key part of this change is to store a UnitId in the
`UsageHomeModule` and `UsageHomeModuleInterface`.
* Fine-grained dependency tracking is used if the dependency comes from
any home unit.
* We actually look up the right module when checking whether we need to
recompile in the `UsageHomeModuleInterface` case.
These scenarios are both checked by the new tests (
multipleHomeUnits_recomp and multipleHomeUnits_recomp_th )
Fixes #22675
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-fwrite-interface
Involves adding many new NFData instances.
Without forcing Docs, references to the TcGblEnv for each module are retained
by the Docs structure. Usually these are forced when the ModIface is serialised
but not when we aren't writing the interface.
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Add JS backend adapted from the GHCJS project by Luite Stegeman.
Some features haven't been ported or implemented yet. Tests for these
features have been disabled with an associated gitlab ticket.
Bump array submodule
Work funded by IOG.
Co-authored-by: Jeffrey Young <jeffrey.young@iohk.io>
Co-authored-by: Luite Stegeman <stegeman@gmail.com>
Co-authored-by: Josh Meredith <joshmeredith2008@gmail.com>
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Pass FastStrings to functions directly, to make sure the rule
for fsLit "literal" fires.
Remove SDoc indirection in GHCi.UI.Tags and GHC.Unit.Module.Graph.
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Gergo points out that these bindings are tidied, rather than prepd as
the variable claims. Therefore we update the name of the variable to
reflect reality and add a comment to the data type to try to erase any
future confusion.
Fixes #22307
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This change aims to minimize source location information leaking
into interface files, which makes ABI hashes dependent on the
build location.
The `Binary (Located a)` instance has been removed completely.
It seems that the HIE interface still needs the ability to
serialize SrcSpans, but by wrapping the instances, it should
be a lot more difficult to inadvertently add source location
information.
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Lets us avoid some use of `head` and `tail`, and some panics.
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This commit adds three new flags
* -fwrite-if-simplified-core: Writes the whole core program into an interface
file
* -fbyte-code-and-object-code: Generate both byte code and object code
when compiling a file
* -fprefer-byte-code: Prefer to use byte-code if it's available when
running TH splices.
The goal for including the core bindings in an interface file is to be able to restart the compiler pipeline
at the point just after simplification and before code generation. Once compilation is
restarted then code can be created for the byte code backend.
This can significantly speed up
start-times for projects in GHCi. HLS already implements its own version of these extended interface
files for this reason.
Preferring to use byte-code means that we can avoid some potentially
expensive code generation steps (see #21700)
* Producing object code is much slower than producing bytecode, and normally you
need to compile with `-dynamic-too` to produce code in the static and dynamic way, the
dynamic way just for Template Haskell execution when using a dynamically linked compiler.
* Linking many large object files, which happens once per splice, can be quite
expensive compared to linking bytecode.
And you can get GHC to compile the necessary byte code so
`-fprefer-byte-code` has access to it by using
`-fbyte-code-and-object-code`.
Fixes #21067
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• Delete some dead code, largely under `GHC.Utils`.
• Clean up a few definitions in `GHC.Utils.(Misc, Monad)`.
• Clean up `GHC.Types.SrcLoc`.
• Derive stock `Functor, Foldable, Traversable` for more types.
• Derive more instances for newtypes.
Bump haddock submodule.
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This fixes various typos and spelling mistakes
in the compiler.
Fixes #21891
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This MR adds diagnostic codes, assigning unique numeric codes to
error and warnings, e.g.
error: [GHC-53633]
Pattern match is redundant
This is achieved as follows:
- a type family GhcDiagnosticCode that gives the diagnostic code
for each diagnostic constructor,
- a type family ConRecursInto that specifies whether to recur into
an argument of the constructor to obtain a more fine-grained code
(e.g. different error codes for different 'deriving' errors),
- generics machinery to generate the value-level function assigning
each diagnostic its error code; see Note [Diagnostic codes using generics]
in GHC.Types.Error.Codes.
The upshot is that, to add a new diagnostic code, contributors only need
to modify the two type families mentioned above. All logic relating to
diagnostic codes is thus contained to the GHC.Types.Error.Codes module,
with no code duplication.
This MR also refactors error message datatypes a bit, ensuring we can
derive Generic for them, and cleans up the logic around constraint
solver reports by splitting up 'TcSolverReportInfo' into separate
datatypes (see #20772).
Fixes #21684
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This patch fixes quite a tricky leak where we would end up retaining
stale ModDetails due to rehydrating modules against non-finalised
interfaces.
== Loops with multiple boot files
It is possible for a module graph to have a loop (SCC, when ignoring boot files)
which requires multiple boot files to break. In this case we must perform the
necessary hydration steps before and after compiling modules which have boot files
which are described above for corectness but also perform an additional hydration step
at the end of the SCC to remove space leaks.
Consider the following example:
┌───────┐ ┌───────┐
│ │ │ │
│ A │ │ B │
│ │ │ │
└─────┬─┘ └───┬───┘
│ │
┌────▼─────────▼──┐
│ │
│ C │
└────┬─────────┬──┘
│ │
┌────▼──┐ ┌───▼───┐
│ │ │ │
│ A-boot│ │ B-boot│
│ │ │ │
└───────┘ └───────┘
A, B and C live together in a SCC. Say we compile the modules in order
A-boot, B-boot, C, A, B then when we compile A we will perform the hydration steps
(because A has a boot file). Therefore C will be hydrated relative to A, and the
ModDetails for A will reference C/A. Then when B is compiled C will be rehydrated again,
and so B will reference C/A,B, its interface will be hydrated relative to both A and B.
Now there is a space leak because say C is a very big module, there are now two different copies of
ModDetails kept alive by modules A and B.
The way to avoid this space leak is to rehydrate an entire SCC together at the
end of compilation so that all the ModDetails point to interfaces for .hs files.
In this example, when we hydrate A, B and C together then both A and B will refer to
C/A,B.
See #21900 for some more discussion.
-------------------------------------------------------
In addition to this simple case, there is also the potential for a leak
during parallel upsweep which is also fixed by this patch. Transcibed is
Note [ModuleNameSet, efficiency and space leaks]
Note [ModuleNameSet, efficiency and space leaks]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
During unsweep the results of compiling modules are placed into a MVar, to find
the environment the module needs to compile itself in the MVar is consulted and
the HomeUnitGraph is set accordingly. The reason we do this is that precisely tracking
module dependencies and recreating the HUG from scratch each time is very expensive.
In serial mode (-j1), this all works out fine because a module can only be compiled after
its dependencies have finished compiling and not interleaved with compiling module loops.
Therefore when we create the finalised or no loop interfaces, the HUG only contains
finalised interfaces.
In parallel mode, we have to be more careful because the HUG variable can contain
non-finalised interfaces which have been started by another thread. In order to avoid
a space leak where a finalised interface is compiled against a HPT which contains a
non-finalised interface we have to restrict the HUG to only the visible modules.
The visible modules is recording in the ModuleNameSet, this is propagated upwards
whilst compiling and explains which transitive modules are visible from a certain point.
This set is then used to restrict the HUG before the module is compiled to only
the visible modules and thus avoiding this tricky space leak.
Efficiency of the ModuleNameSet is of utmost importance because a union occurs for
each edge in the module graph. Therefore the set is represented directly as an IntSet
which provides suitable performance, even using a UniqSet (which is backed by an IntMap) is
too slow. The crucial test of performance here is the time taken to a do a no-op build in --make mode.
See test "jspace" for an example which used to trigger this problem.
Fixes #21900
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to previous ModuleGraphs, in particular the lazy `mg_non_boot` field.
This manifests in `extendMG`.
Solution: Delete `mg_non_boot` as it is only used for `mgLookupModule`, which
is only called in two places in the compiler, and should only be called at most
once for every home unit:
GHC.Driver.Make:
mainModuleSrcPath :: Maybe String
mainModuleSrcPath = do
ms <- mgLookupModule mod_graph (mainModIs hue)
ml_hs_file (ms_location ms)
GHCI.UI:
listModuleLine modl line = do
graph <- GHC.getModuleGraph
let this = GHC.mgLookupModule graph modl
Instead `mgLookupModule` can be a linear function that looks through the entire
list of `ModuleGraphNodes`
Fixes #21816
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We were attempting to rehydrate all dependencies of a particular module,
but we actually only needed to rehydrate those of the current package
(as those are the ones participating in the loop).
This fixes loading GHC into a multi-unit session.
Fixes #21814
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ModuleName used to live in GHC.Unit.Module.Name. In this commit, the
definition of ModuleName and its associated functions are moved to
Language.Haskell.Syntax.Module.Name according to the current plan
towards making the AST GHC-independent.
The instances for ModuleName for Outputable, Uniquable and Binary were
moved to the module in which the class is defined because these instances
depend on GHC.
The instance of Eq for ModuleName is slightly changed to no longer
depend on unique explicitly and instead uses FastString's instance of
Eq.
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Move the GHC-independent definitions from GHC.Hs.ImpExp to
Language.Haskell.Syntax.ImpExp with the required TTG extension fields
such as to keep the AST independent from GHC.
This is progress towards having the haskell-syntax package, as described
in #21592
Bumps haddock submodule
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Move the definition of HsModule defined in GHC.Hs to
Language.Haskell.Syntax with an added TTG parameter and corresponding
extension fields.
This is progress towards having the haskell-syntax package, as described
in #21592
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This patch typechecks record updates by desugaring them inside
the typechecker using the HsExpansion mechanism, and then typechecking
this desugared result.
Example:
data T p q = T1 { x :: Int, y :: Bool, z :: Char }
| T2 { v :: Char }
| T3 { x :: Int }
| T4 { p :: Float, y :: Bool, x :: Int }
| T5
The record update `e { x=e1, y=e2 }` desugars as follows
e { x=e1, y=e2 }
===>
let { x' = e1; y' = e2 } in
case e of
T1 _ _ z -> T1 x' y' z
T4 p _ _ -> T4 p y' x'
The desugared expression is put into an HsExpansion, and we typecheck
that.
The full details are given in Note [Record Updates] in GHC.Tc.Gen.Expr.
Fixes #2595 #3632 #10808 #10856 #16501 #18311 #18802 #21158 #21289
Updates haddock submodule
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With this change, `Backend` becomes an abstract type
(there are no more exposed value constructors).
Decisions that were formerly made by asking "is the
current back end equal to (or different from) this named value
constructor?" are now made by interrogating the back end about
its properties, which are functions exported by `GHC.Driver.Backend`.
There is a description of how to migrate code using `Backend` in the
user guide.
Clients using the GHC API can find a backdoor to access the Backend
datatype in GHC.Driver.Backend.Internal.
Bumps haddock submodule.
Fixes #20927
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This function is used by API clients (hls).
This supercedes !6922
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Fixes #20935 and #20924
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Names appearing in Haddock docstrings are lexed and renamed like any other names
appearing in the AST. We currently rename names irrespective of the namespace,
so both type and constructor names corresponding to an identifier will appear in
the docstring. Haddock will select a given name as the link destination based on
its own heuristics.
This patch also restricts the limitation of `-haddock` being incompatible with
`Opt_KeepRawTokenStream`.
The export and documenation structure is now computed in GHC and serialised in
.hi files. This can be used by haddock to directly generate doc pages without
reparsing or renaming the source. At the moment the operation of haddock
is not modified, that's left to a future patch.
Updates the haddock submodule with the minimum changes needed.
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As noted in #21071 we were missing adding this edge so there were
situations where the .hs file would get compiled before the .hs-boot
file which leads to issues with -j.
I fixed this properly by adding the edge in downsweep so the definition
of nodeDependencies can be simplified to avoid adding this dummy edge
in.
There are plenty of tests which seem to have these redundant boot files
anyway so no new test. #21094 tracks the more general issue of
identifying redundant hs-boot and SOURCE imports.
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In the case when we tell moduleGraphNodes to drop hs-boot files the idea
is to collapse hs-boot files into their hs file nodes. In the old code
* nodeDependencies changed edges from IsBoot to NonBoot
* moduleGraphNodes just dropped boot file nodes
The net result is that any dependencies of the hs-boot files themselves
were dropped. The correct thing to do is
* nodeDependencies changes edges from IsBoot to NonBoot
* moduleGraphNodes merges dependencies of IsBoot and NonBoot nodes.
The result is a properly quotiented dependency graph which contains no
hs-boot files nor hs-boot file edges.
Why this didn't cause endless issues when compiling with boot files, we
will never know.
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It turns out this job hasn't been running for quite a while (perhaps
ever) so there are quite a few failures when running the linter locally.
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The idea of the needsTemplateHaskellOrQQ query is to check if any of the
modules in a module graph need Template Haskell then enable -dynamic-too
if necessary. This is quite imprecise though as it will enable
-dynamic-too for all modules in the module graph even if only one module
uses template haskell, with multiple home units, this is obviously even
worse.
With -fno-code we already have similar logic to enable code generation
just for the modules which are dependeded on my TemplateHaskell modules
so we use the same code path to decide whether to enable -dynamic-too
rather than using this big hammer.
This is part of the larger overall goal of moving as much statically
known configuration into the downsweep as possible in order to have
fully decided the build plan and all the options before starting to
build anything.
I also included a fix to #21095, a long standing bug with with the logic
which is supposed to enable the external interpreter if we don't have
the internal interpreter.
Fixes #20696 #21095
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It was unused in the compiler so I have removed it to streamline
ModuleGraph.
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`hscCompileCoreExprHook` is changed to return a list of `Module`s required
by a splice. These modules are accumulated in the TcGblEnv (tcg_th_needed_mods).
Dependencies on the object files of these modules are recording in the
interface.
The data structures in `LoaderState` are replaced with more efficient versions
to keep track of all the information required. The
MultiLayerModulesTH_Make allocations increase slightly but runtime is
faster.
Fixes #20604
-------------------------
Metric Increase:
MultiLayerModulesTH_Make
-------------------------
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This does three major things:
* Enforce the invariant that all strict fields must contain tagged
pointers.
* Try to predict the tag on bindings in order to omit tag checks.
* Allows functions to pass arguments unlifted (call-by-value).
The former is "simply" achieved by wrapping any constructor allocations with
a case which will evaluate the respective strict bindings.
The prediction is done by a new data flow analysis based on the STG
representation of a program. This also helps us to avoid generating
redudant cases for the above invariant.
StrictWorkers are created by W/W directly and SpecConstr indirectly.
See the Note [Strict Worker Ids]
Other minor changes:
* Add StgUtil module containing a few functions needed by, but
not specific to the tag analysis.
-------------------------
Metric Decrease:
T12545
T18698b
T18140
T18923
LargeRecord
Metric Increase:
LargeRecord
ManyAlternatives
ManyConstructors
T10421
T12425
T12707
T13035
T13056
T13253
T13253-spj
T13379
T15164
T18282
T18304
T18698a
T1969
T20049
T3294
T4801
T5321FD
T5321Fun
T783
T9233
T9675
T9961
T19695
WWRec
-------------------------
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Here we introduce a new data structure, RoughMap, inspired by the
previous `RoughTc` matching mechanism for checking instance matches.
This allows [Fam]InstEnv to be implemented as a trie indexed by these
RoughTc signatures, reducing the complexity of instance lookup and
FamInstEnv merging (done during the family instance conflict test)
from O(n) to O(log n).
The critical performance improvement currently realised by this patch is
in instance matching. In particular the RoughMap mechanism allows us to
discount many potential instances which will never match for constraints
involving type variables (see Note [Matching a RoughMap]). In realistic
code bases matchInstEnv was accounting for 50% of typechecker time due
to redundant work checking instances when simplifying instance contexts
when deriving instances. With this patch the cost is significantly
reduced.
The larger constants in InstEnv creation do mean that a few small
tests regress in allocations slightly. However, the runtime of T19703 is
reduced by a factor of 4. Moreover, the compilation time of the Cabal
library is slightly improved.
A couple of test cases are included which demonstrate significant
improvements in compile time with this patch.
This unfortunately does not fix the testcase provided in #19703 but does
fix #20933
-------------------------
Metric Decrease:
T12425
Metric Increase:
T13719
T9872a
T9872d
hard_hole_fits
-------------------------
Co-authored-by: Matthew Pickering <matthewtpickering@gmail.com>
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Multiple home units allows you to load different packages which may depend on
each other into one GHC session. This will allow both GHCi and HLS to support
multi component projects more naturally.
Public Interface
~~~~~~~~~~~~~~~~
In order to specify multiple units, the -unit @⟨filename⟩ flag
is given multiple times with a response file containing the arguments for each unit.
The response file contains a newline separated list of arguments.
```
ghc -unit @unitLibCore -unit @unitLib
```
where the `unitLibCore` response file contains the normal arguments that cabal would pass to `--make` mode.
```
-this-unit-id lib-core-0.1.0.0
-i
-isrc
LibCore.Utils
LibCore.Types
```
The response file for lib, can specify a dependency on lib-core, so then modules in lib can use modules from lib-core.
```
-this-unit-id lib-0.1.0.0
-package-id lib-core-0.1.0.0
-i
-isrc
Lib.Parse
Lib.Render
```
Then when the compiler starts in --make mode it will compile both units lib and lib-core.
There is also very basic support for multiple home units in GHCi, at the
moment you can start a GHCi session with multiple units but only the
:reload is supported. Most commands in GHCi assume a single home unit,
and so it is additional work to work out how to modify the interface to
support multiple loaded home units.
Options used when working with Multiple Home Units
There are a few extra flags which have been introduced specifically for
working with multiple home units. The flags allow a home unit to pretend
it’s more like an installed package, for example, specifying the package
name, module visibility and reexported modules.
-working-dir ⟨dir⟩
It is common to assume that a package is compiled in the directory
where its cabal file resides. Thus, all paths used in the compiler
are assumed to be relative to this directory. When there are
multiple home units the compiler is often not operating in the
standard directory and instead where the cabal.project file is
located. In this case the -working-dir option can be passed which
specifies the path from the current directory to the directory the
unit assumes to be it’s root, normally the directory which contains
the cabal file.
When the flag is passed, any relative paths used by the compiler are
offset by the working directory. Notably this includes -i and
-I⟨dir⟩ flags.
-this-package-name ⟨name⟩
This flag papers over the awkward interaction of the PackageImports
and multiple home units. When using PackageImports you can specify
the name of the package in an import to disambiguate between modules
which appear in multiple packages with the same name.
This flag allows a home unit to be given a package name so that you
can also disambiguate between multiple home units which provide
modules with the same name.
-hidden-module ⟨module name⟩
This flag can be supplied multiple times in order to specify which
modules in a home unit should not be visible outside of the unit it
belongs to.
The main use of this flag is to be able to recreate the difference
between an exposed and hidden module for installed packages.
-reexported-module ⟨module name⟩
This flag can be supplied multiple times in order to specify which
modules are not defined in a unit but should be reexported. The
effect is that other units will see this module as if it was defined
in this unit.
The use of this flag is to be able to replicate the reexported
modules feature of packages with multiple home units.
Offsetting Paths in Template Haskell splices
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When using Template Haskell to embed files into your program,
traditionally the paths have been interpreted relative to the directory
where the .cabal file resides. This causes problems for multiple home
units as we are compiling many different libraries at once which have
.cabal files in different directories.
For this purpose we have introduced a way to query the value of the
-working-dir flag to the Template Haskell API. By using this function we
can implement a makeRelativeToProject function which offsets a path
which is relative to the original project root by the value of
-working-dir.
```
import Language.Haskell.TH.Syntax ( makeRelativeToProject )
foo = $(makeRelativeToProject "./relative/path" >>= embedFile)
```
> If you write a relative path in a Template Haskell splice you should use the makeRelativeToProject function so that your library works correctly with multiple home units.
A similar function already exists in the file-embed library. The
function in template-haskell implements this function in a more robust
manner by honouring the -working-dir flag rather than searching the file
system.
Closure Property for Home Units
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
For tools or libraries using the API there is one very important closure
property which must be adhered to:
> Any dependency which is not a home unit must not (transitively) depend
on a home unit.
For example, if you have three packages p, q and r, then if p depends on
q which depends on r then it is illegal to load both p and r as home
units but not q, because q is a dependency of the home unit p which
depends on another home unit r.
If you are using GHC by the command line then this property is checked,
but if you are using the API then you need to check this property
yourself. If you get it wrong you will probably get some very confusing
errors about overlapping instances.
Limitations of Multiple Home Units
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
There are a few limitations of the initial implementation which will be smoothed out on user demand.
* Package thinning/renaming syntax is not supported
* More complicated reexports/renaming are not yet supported.
* It’s more common to run into existing linker bugs when loading a
large number of packages in a session (for example #20674, #20689)
* Backpack is not yet supported when using multiple home units.
* Dependency chasing can be quite slow with a large number of
modules and packages.
* Loading wired-in packages as home units is currently not supported
(this only really affects GHC developers attempting to load
template-haskell).
* Barely any normal GHCi features are supported, it would be good to
support enough for ghcid to work correctly.
Despite these limitations, the implementation works already for nearly
all packages. It has been testing on large dependency closures,
including the whole of head.hackage which is a total of 4784 modules
from 452 packages.
Internal Changes
~~~~~~~~~~~~~~~~
* The biggest change is that the HomePackageTable is replaced with the
HomeUnitGraph. The HomeUnitGraph is a map from UnitId to HomeUnitEnv,
which contains information specific to each home unit.
* The HomeUnitEnv contains:
- A unit state, each home unit can have different package db flags
- A set of dynflags, each home unit can have different flags
- A HomePackageTable
* LinkNode: A new node type is added to the ModuleGraph, this is used to
place the linking step into the build plan so linking can proceed in
parralel with other packages being built.
* New invariant: Dependencies of a ModuleGraphNode can be completely
determined by looking at the value of the node. In order to achieve
this, downsweep now performs a more complete job of downsweeping and
then the dependenices are recorded forever in the node rather than
being computed again from the ModSummary.
* Some transitive module calculations are rewritten to use the
ModuleGraph which is more efficient.
* There is always an active home unit, which simplifies modifying a lot
of the existing API code which is unit agnostic (for example, in the
driver).
The road may be bumpy for a little while after this change but the
basics are well-tested.
One small metric increase, which we accept and also submodule update to
haddock which removes ExtendedModSummary.
Closes #10827
-------------------------
Metric Increase:
MultiLayerModules
-------------------------
Co-authored-by: Fendor <power.walross@gmail.com>
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Instead, introduce plusInstalledModuleEnv
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There is more than one possible Semigroup and it is not needed since plusModuleEnv can be used directly
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Note [Hydrating Modules]
~~~~~~~~~~~~~~~~~~~~~~~~
What is hydrating a module?
* There are two versions of a module, the ModIface is the on-disk version and the ModDetails is a fleshed-out in-memory version.
* We can **hydrate** a ModIface in order to obtain a ModDetails.
Hydration happens in three different places
* When an interface file is initially loaded from disk, it has to be hydrated.
* When a module is finished compiling, we hydrate the ModIface in order to generate
the version of ModDetails which exists in memory (see Note)
* When dealing with boot files and module loops (see Note [Rehydrating Modules])
Note [Rehydrating Modules]
~~~~~~~~~~~~~~~~~~~~~~~~~~~
If a module has a boot file then it is critical to rehydrate the modules on
the path between the two.
Suppose we have ("R" for "recursive"):
```
R.hs-boot: module R where
data T
g :: T -> T
A.hs: module A( f, T, g ) where
import {-# SOURCE #-} R
data S = MkS T
f :: T -> S = ...g...
R.hs: module R where
data T = T1 | T2 S
g = ...f...
```
After compiling A.hs we'll have a TypeEnv in which the Id for `f` has a type
type uses the AbstractTyCon T; and a TyCon for `S` that also mentions that same
AbstractTyCon. (Abstract because it came from R.hs-boot; we know nothing about
it.)
When compiling R.hs, we build a TyCon for `T`. But that TyCon mentions `S`, and
it currently has an AbstractTyCon for `T` inside it. But we want to build a
fully cyclic structure, in which `S` refers to `T` and `T` refers to `S`.
Solution: **rehydration**. *Before compiling `R.hs`*, rehydrate all the
ModIfaces below it that depend on R.hs-boot. To rehydrate a ModIface, call
`typecheckIface` to convert it to a ModDetails. It's just a de-serialisation
step, no type inference, just lookups.
Now `S` will be bound to a thunk that, when forced, will "see" the final binding
for `T`; see [Tying the knot](https://gitlab.haskell.org/ghc/ghc/-/wikis/commentary/compiler/tying-the-knot).
But note that this must be done *before* compiling R.hs.
When compiling R.hs, the knot-tying stuff above will ensure that `f`'s unfolding
mentions the `LocalId` for `g`. But when we finish R, we carefully ensure that
all those `LocalIds` are turned into completed `GlobalIds`, replete with
unfoldings etc. Alas, that will not apply to the occurrences of `g` in `f`'s
unfolding. And if we leave matters like that, they will stay that way, and *all*
subsequent modules that import A will see a crippled unfolding for `f`.
Solution: rehydrate both R and A's ModIface together, right after completing R.hs.
We only need rehydrate modules that are
* Below R.hs
* Above R.hs-boot
There might be many unrelated modules (in the home package) that don't need to be
rehydrated.
This dark corner is the subject of #14092.
Suppose we add to our example
```
X.hs module X where
import A
data XT = MkX T
fx = ...g...
```
If in `--make` we compile R.hs-boot, then A.hs, then X.hs, we'll get a `ModDetails` for `X` that has an AbstractTyCon for `T` in the the argument type of `MkX`. So:
* Either we should delay compiling X until after R has beeen compiled.
* Or we should rehydrate X after compiling R -- because it transitively depends on R.hs-boot.
Ticket #20200 has exposed some issues to do with the knot-tying logic in GHC.Make, in `--make` mode.
this particular issue starts [here](https://gitlab.haskell.org/ghc/ghc/-/issues/20200#note_385758).
The wiki page [Tying the knot](https://gitlab.haskell.org/ghc/ghc/-/wikis/commentary/compiler/tying-the-knot) is helpful.
Also closely related are
* #14092
* #14103
Fixes tickets #20200 #20561
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Two reasons for this change:
1. Avoid computing the transitive dependencies when compiling each
module, this can save a lot of repeated work.
2. More robust to forthcoming changes to support multiple home units.
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Use an (Raw)PkgQual datatype instead of `Maybe FastString` to represent
package imports. Factorize the code that renames RawPkgQual into PkgQual
in function `rnPkgQual`. Renaming consists in checking if the FastString
is the magic "this" keyword, the home-unit unit-id or something else.
Bump haddock submodule
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When we are not writing a ModIface to disk then the result can retain a
lot of stuff. For example, in the case I was debugging the DocDeclsMap
field was holding onto the entire HomePackageTable due to a single
unforced thunk. Therefore, now if we're not going to write the interface
then we still force deeply it in order to remove these thunks.
The fields in the data structure are not made strict because when we
read the field from the interface we don't want to load it immediately
as there are parts of an interface which are unused a lot of the time.
Also added a note to explain why not all the fields in a ModIface field
are strict.
The result of this is being able to load Agda in ghci and not leaking
information across subsequent reloads.
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At the moment if `-dynamic-too` fails then we rerun the whole pipeline
as if we were just in `-dynamic` mode. I argue this is a misfeature and
we should remove the so-called `DT_Failed` mode.
In what situations do we fall back to `DT_Failed`?
1. If the `dyn_hi` file corresponding to a `hi` file is missing completely.
2. If the interface hash of `dyn_hi` doesn't match the interface hash of `hi`.
What happens in `DT_Failed` mode?
* The whole compiler pipeline is rerun as if the user had just passed `-dynamic`.
* Therefore `dyn_hi/dyn_o` files are used which don't agree with the
`hi/o` files. (As evidenced by `dynamicToo001` test).
* This is very confusing as now a single compiler invocation has
produced further `hi`/`dyn_hi` files which are different to each
other.
Why should we remove it?
* In `--make` mode, which is predominately used `DT_Failed` does not
work (#19782), there can't be users relying on this functionality.
* In `-c` mode, the recovery doesn't fix the root issue, which is the
`dyn_hi` and `hi` files are mismatched. We should instead produce an
error and pass responsibility to the build system using `-c` to ensure
that the prerequisites for `-dynamic-too` (dyn_hi/hi) files are there
before we start compiling.
* It is a misfeature to support use cases like `dynamicToo001` which
allow you to mix different versions of dynamic/non-dynamic interface
files. It's more likely to lead to subtle bugs in your resulting
programs where out-dated build products are used rather than a
deliberate choice.
* In practice, people are usually compiling with `-dynamic-too` rather
than separately with `-dynamic` and `-static`, so the build products
always match and `DT_Failed` is only entered due to compiler bugs (see
!6583)
What should we do instead?
* In `--make` mode, for home packages check during recompilation
checking that `dyn_hi` and `hi` are both present and agree, recompile
the modules if they do not.
* For package modules, when loading the interface check that `dyn_hi`
and `hi` are there and that they agree but fail with an
error message if they are not.
* In `--oneshot` mode, fail with an error message if the right files
aren't already there.
Closes #19782 #20446 #9176 #13616
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