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| author | David Terei <davidterei@gmail.com> | 2013-08-19 16:00:55 -0700 |
|---|---|---|
| committer | David Terei <davidterei@gmail.com> | 2013-08-19 16:00:55 -0700 |
| commit | 6cc7d3f120d62d15ad6a2cc3393c3f744c93ff18 (patch) | |
| tree | ec059df0947c965bc70a24cec9f352a23c747197 | |
| parent | 4eeccc1ce80df7cc96bf72a5cd8a2397b03e2b35 (diff) | |
| download | haskell-6cc7d3f120d62d15ad6a2cc3393c3f744c93ff18.tar.gz | |
Add note on isSafeOverlap field.
| -rw-r--r-- | compiler/basicTypes/BasicTypes.lhs | 3 | ||||
| -rw-r--r-- | compiler/types/InstEnv.lhs | 18 |
2 files changed, 13 insertions, 8 deletions
diff --git a/compiler/basicTypes/BasicTypes.lhs b/compiler/basicTypes/BasicTypes.lhs index 35b0ac5b3d..838e368ea6 100644 --- a/compiler/basicTypes/BasicTypes.lhs +++ b/compiler/basicTypes/BasicTypes.lhs @@ -362,6 +362,9 @@ instance Outputable RecFlag where %************************************************************************ \begin{code} +-- | The semantics allowed for overlapping instances for a particular +-- instance. See Note [Safe Haskell isSafeOverlap] (in `InstEnv.lhs`) for a +-- explanation of the `isSafeOverlap` field. data OverlapFlag -- | This instance must not overlap another = NoOverlap { isSafeOverlap :: Bool } diff --git a/compiler/types/InstEnv.lhs b/compiler/types/InstEnv.lhs index 18d67d8053..6b6ddcdbb3 100644 --- a/compiler/types/InstEnv.lhs +++ b/compiler/types/InstEnv.lhs @@ -582,14 +582,16 @@ lookupInstEnv (pkg_ie, home_ie) cls tys -- misleading (complaining of multiple matches when some should be -- overlapped away) - -- Safe Haskell: We restrict code compiled in 'Safe' mode from - -- overriding code compiled in any other mode. The rational is - -- that code compiled in 'Safe' mode is code that is untrusted - -- by the ghc user. So we shouldn't let that code change the - -- behaviour of code the user didn't compile in 'Safe' mode - -- since that's the code they trust. So 'Safe' instances can only - -- overlap instances from the same module. A same instance origin - -- policy for safe compiled instances. + -- NOTE [Safe Haskell isSafeOverlap] + -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + -- We restrict code compiled in 'Safe' mode from overriding code + -- compiled in any other mode. The rational is that code compiled + -- in 'Safe' mode is code that is untrusted by the ghc user. So + -- we shouldn't let that code change the behaviour of code the + -- user didn't compile in 'Safe' mode since that's the code they + -- trust. So 'Safe' instances can only overlap instances from the + -- same module. A same instance origin policy for safe compiled + -- instances. check_safe match@(inst,_) others = case isSafeOverlap (is_flag inst) of -- most specific isn't from a Safe module so OK |