[Git][ghc/ghc][wip/t25571] 3 commits: Add flag to control whether self-recompilation information is written to interface

[Matthew Pickering (@mpickering)]

Matthew Pickering pushed to branch wip/t25571 at Glasgow Haskell Compiler / GHC


Commits:
a510b861 by Matthew Pickering at 2025-03-06T11:43:23+00:00
Add flag to control whether self-recompilation information is written to interface

This patch adds the flag -fwrite-if-self-recomp which controls whether
interface files contain the information necessary to answer the
question:

  Do I need to recompile myself or is this current interface file
  suitable?

Why? Most packages are only built once either by a distribution or cabal
and then placed into an immutable store, after which we will never ask
this question. Therefore we can derive two benefits from omitting this
information.

* Primary motivation: It vastly reduces the surface area for creating
  non-deterministic interface files. See issue #10424 which motivated a
  proper fix to that issue. Distributions have long contained versions
  of GHC which just have broken self-recompilation checking (in order to
  get deterministic interface files).

* Secondary motivation: This reduces the size of interface files
  slightly.. the `mi_usages` field can be quite big but probably this
  isn't such a great benefit.

* Third motivation: Conceptually clarity about which parts of an
  interface file are used in order to **communicate** with subsequent
  packages about the **interface** for a module. And which parts are
  used to self-communicate during recompilation checking.

The main tracking issue is #22188 but fixes issues such as #10424 in a
proper way.

- - - - -
5b05c27b by Matthew Pickering at 2025-03-06T11:43:23+00:00
Disable self recomp in release flavour

The interface files that we distribute should not contain any
information which is used by the recompilation checking logic since
source file will never be compiled again.

I am not 100% sure this won't cause unexpected issues, there many be
downstream consumers which are incorrectly using the information from
interfaces, but this commit can be reverted if we detect issues.

- - - - -
21c971e0 by Matthew Pickering at 2025-03-06T11:43:23+00:00
iface: Store flags in interface files

When reporting the reason why a module is recompiled (using
`-dump-hi-diffs`), it is much more informative to inform the user about
which flag exactly has changed, rather than just an opaque reference to
a hash.

Now, when the user enables `-fwrite-if-self-recomp-flags`
there is a difference the precise part of the flags is
reported:

```
codegen flags changed:
before: [Opt_NoTypeableBinds, Opt_OmitYields]
after: [Opt_NoTypeableBinds, Opt_OmitYields, Opt_DictsStrict]
```

Fixes #25571

- - - - -


35 changed files:

- compiler/GHC.hs
- compiler/GHC/Core/Opt/CallerCC/Types.hs
- compiler/GHC/Driver/DynFlags.hs
- compiler/GHC/Driver/Flags.hs
- + compiler/GHC/Driver/IncludeSpecs.hs
- compiler/GHC/Driver/Main.hs
- compiler/GHC/Driver/Make.hs
- compiler/GHC/Driver/Session.hs
- compiler/GHC/HsToCore.hs
- compiler/GHC/Iface/Binary.hs
- compiler/GHC/Iface/Env.hs
- + compiler/GHC/Iface/Flags.hs
- compiler/GHC/Iface/Load.hs
- compiler/GHC/Iface/Make.hs
- compiler/GHC/Iface/Recomp.hs
- compiler/GHC/Iface/Recomp/Flags.hs
- + compiler/GHC/Iface/Recomp/Types.hs
- compiler/GHC/Types/ProfAuto.hs
- compiler/GHC/Types/SafeHaskell.hs
- compiler/GHC/Unit/Module/ModGuts.hs
- compiler/GHC/Unit/Module/ModIface.hs
- compiler/ghc.cabal.in
- docs/users_guide/phases.rst
- hadrian/doc/flavours.md
- hadrian/src/Flavour.hs
- hadrian/src/Settings/Flavours/Release.hs
- testsuite/tests/count-deps/CountDepsAst.stdout
- testsuite/tests/count-deps/CountDepsParser.stdout
- + testsuite/tests/driver/self-recomp/Makefile
- + testsuite/tests/driver/self-recomp/SelfRecomp01.hs
- + testsuite/tests/driver/self-recomp/SelfRecomp02.hs
- + testsuite/tests/driver/self-recomp/SelfRecomp03.hs
- + testsuite/tests/driver/self-recomp/SelfRecomp04.hs
- + testsuite/tests/driver/self-recomp/SelfRecomp04.stdout
- + testsuite/tests/driver/self-recomp/all.T


The diff was not included because it is too large.


View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/fbe973e4aff63e953415337cba57aad42fb9fc75...21c971e03ab175dd416b74931d245ed92d4f9634

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/fbe973e4aff63e953415337cba57aad42fb9fc75...21c971e03ab175dd416b74931d245ed92d4f9634
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