summaryrefslogtreecommitdiff
path: root/compiler/GHC/Unit/Module/ModGuts.hs
diff options
context:
space:
mode:
authorMatthew Pickering <matthewtpickering@gmail.com>2022-12-13 12:30:36 +0000
committerMatthew Pickering <matthewtpickering@gmail.com>2022-12-23 11:22:25 +0000
commit40c9da19decb68e1bf4be6fef7b0592c19a8cacd (patch)
treeda86ac3d580f161cb971bfba6edae205f11a9d7c /compiler/GHC/Unit/Module/ModGuts.hs
parent16a1bcd1d72c7a4567671f6a7f610df3fc477519 (diff)
downloadhaskell-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 'compiler/GHC/Unit/Module/ModGuts.hs')
-rw-r--r--compiler/GHC/Unit/Module/ModGuts.hs2
1 files changed, 1 insertions, 1 deletions
diff --git a/compiler/GHC/Unit/Module/ModGuts.hs b/compiler/GHC/Unit/Module/ModGuts.hs
index d54e836d71..9f14ba9165 100644
--- a/compiler/GHC/Unit/Module/ModGuts.hs
+++ b/compiler/GHC/Unit/Module/ModGuts.hs
@@ -52,7 +52,7 @@ data ModGuts
mg_exports :: ![AvailInfo], -- ^ What it exports
mg_deps :: !Dependencies, -- ^ What it depends on, directly or
-- otherwise
- mg_usages :: ![Usage], -- ^ What was used? Used for interfaces.
+ mg_usages :: !(Maybe [Usage]), -- ^ What was used? Used for interfaces.
mg_used_th :: !Bool, -- ^ Did we run a TH splice?
mg_rdr_env :: !GlobalRdrEnv, -- ^ Top-level lexical environment