From 357f273838e874d29717c90ab2cf3ea802550e97 Mon Sep 17 00:00:00 2001
From: Sebastian Graf <sebastian.graf@kit.edu>
Date: Fri, 5 May 2023 09:44:30 +0200
Subject: [PATCH] Deactivate -fcatch-nonexhaustive-cases in ghc-bignum (#23345)
---
libraries/ghc-bignum/ghc-bignum.cabal | 12 ++++++++----
libraries/ghc-bignum/src/GHC/Num/BigNat.hs | 19 +++++++++++++++++++
2 files changed, 27 insertions(+), 4 deletions(-)
diff --git a/libraries/ghc-bignum/ghc-bignum.cabal b/libraries/ghc-bignum/ghc-bignum.cabal
index 45bb2b904dea..994a4a6aeabe 100644
--- a/libraries/ghc-bignum/ghc-bignum.cabal
+++ b/libraries/ghc-bignum/ghc-bignum.cabal
@@ -84,10 +84,14 @@ library
ghc-options: -Wall
cc-options: -std=c99 -Wall
- -- GHC has wired-in IDs from the ghc-bignum package. Hence the unit-id
- -- of the package should not contain the version: i.e. it must be
- -- "ghc-bignum" and not "ghc-bignum-1.0".
- ghc-options: -this-unit-id ghc-bignum
+ ghc-options:
+ -- GHC has wired-in IDs from the ghc-bignum package. Hence the unit-id
+ -- of the package should not contain the version: i.e. it must be
+ -- "ghc-bignum" and not "ghc-bignum-1.0".
+ -this-unit-id ghc-bignum
+
+ -- See Note [ghc-bignum and error symbols]
+ -fno-catch-nonexhaustive-cases
if flag(gmp)
cpp-options: -DBIGNUM_GMP
diff --git a/libraries/ghc-bignum/src/GHC/Num/BigNat.hs b/libraries/ghc-bignum/src/GHC/Num/BigNat.hs
index efe78f10c901..21b07cb8300f 100644
--- a/libraries/ghc-bignum/src/GHC/Num/BigNat.hs
+++ b/libraries/ghc-bignum/src/GHC/Num/BigNat.hs
@@ -1645,3 +1645,22 @@ instance Ord BigNat where
BN# a > BN# b = bigNatGt a b
BN# a >= BN# b = bigNatGe a b
+{- Note [ghc-bignum and error symbols]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ghc-bignum only depends on ghc-prim, not base.
+Hence it may not introduce any symbol references to the error symbols in
+Control.Exception.Base such as `patError` or `impossibleError`, otherwise
+we get linker errors.
+
+This implies that
+
+ * Every pattern match must be "obviously complete", otherwise GHC's desugaring
+ inserts `patError`s for the missing cases. "Obviously complete" in the sense
+ that the desugarer is able to infer completeness, so considering type info
+ but not long distance information (as the pattern-match checker would do).
+ * We compile with -fno-catch-nonexhaustive-cases so that we don't risk
+ introducing `impossibleError`
+ * ... probably other similar observations that will be added to this list in
+ the future ...
+
+-}
--
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