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| author | Matthew Pickering <matthewtpickering@gmail.com> | 2022-12-13 12:30:36 +0000 |
|---|---|---|
| committer | Matthew Pickering <matthewtpickering@gmail.com> | 2022-12-23 11:22:25 +0000 |
| commit | 40c9da19decb68e1bf4be6fef7b0592c19a8cacd (patch) | |
| tree | da86ac3d580f161cb971bfba6edae205f11a9d7c /docs/users_guide/using-warnings.rst | |
| parent | 16a1bcd1d72c7a4567671f6a7f610df3fc477519 (diff) | |
| download | haskell-wip/22188.tar.gz | |
Add flag to control whether self-recompilation information is written to interfacewip/22188
This patch adds the flag -fwrite-self-recomp-info 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.
In addition to this, the change alerted me to the incorrect
implemenation of the reifyModule function. See #8489 for more discussion
about how to fix this if anyone was so inclined. For now I just added a
warning `-Wreify-module-missing-info` which triggers if the module you
are trying to reify doesn't have a suitable interface. Interfaces which
are unsuitable include:
* The GHC.Prim interface, which is a fake interface
* Interfaces compiled with -fno-write-self-recomp-info
The main tracking issue is #22188 but fixes issues such as #10424 in a
proper way.
Diffstat (limited to 'docs/users_guide/using-warnings.rst')
| -rw-r--r-- | docs/users_guide/using-warnings.rst | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/docs/users_guide/using-warnings.rst b/docs/users_guide/using-warnings.rst index 977bb69941..d61fc46319 100644 --- a/docs/users_guide/using-warnings.rst +++ b/docs/users_guide/using-warnings.rst @@ -2355,6 +2355,21 @@ of ``-W(no-)*``. triggered whenever this happens, and can be addressed by enabling the extension. +.. ghc-flag:: -Wreify-module-missing-info + :shortdesc: warn when `reifyModule` + :type: dynamic + :reverse: -Wno-reify-module-missing-info + + :since: 9.6.1 + + The `reifyModule` function in the Template Haskell API can fail to find the necessary + information when an interface file is generated with `-fno-write-self-recomp-info`. This + is due to a shortcoming in `reifyModule` tracked by :ghc-ticket:`8489`. + + This flag warns the user when they try to call `reifyModule` on a module where this + situation occurs so that they know the traversal has ended prematurely. + + If you're feeling really paranoid, the :ghc-flag:`-dcore-lint` option is a good choice. It turns on heavyweight intra-pass sanity-checking within GHC. (It checks GHC's sanity, not yours.) |