Add -fno-safe-haskell flag

This flag can be set to turn off the Safe Haskell checks.

Whether a module is marked Safe/Unsafe/Trustworthy is ignored when
this flag to set.

Reviewers: bgamari, tdammers

Reviewed By: tdammers

Subscribers: rwbarton, carter

GHC Trac Issues: #15920

Differential Revision: https://phabricator.haskell.org/D5360

1 files changed, 17 insertions, 0 deletions

diff --git a/docs/users_guide/safe_haskell.rst b/docs/users_guide/safe_haskell.rst
index adf70d2a90..6772d6abf6 100644
--- a/docs/users_guide/safe_haskell.rst
+++ b/docs/users_guide/safe_haskell.rst
@@ -206,6 +206,11 @@ run the plugin, it calls ``RIO.runRIO Danger.runMe`` within the ``IO``
 monad. The application is safe in the knowledge that the only ``IO`` to
 ensue will be to files whose paths were approved by the ``pathOK`` test.
 
+The Safe Haskell checks can be disabled for a module by passing the
+:ghc-flag:`-fno-safe-haskell` flag. This is useful in particular when compiling
+with source plugins as running a plugin marks the module as unsafe and can then
+cause downstream modules to fail the safety checks.
+
 .. _safe-language:
 
 Safe Language
@@ -710,6 +715,18 @@ In summary, Safe Haskell consists of the following three language flags:
     - *Imported Modules* — Under control of module author which ones must be
       trusted.
 
+A flag to disable Safe Haskell checks:
+
+.. ghc-flag:: -fno-safe-haskell
+    :shortdesc: Disable :ref:`Safe Haskell <safe-haskell>`
+    :type: dynamic
+
+    This flag can be enabled to override any declared safety property of the
+    module (Safe, Unsafe, Trustworthy) so compilation proceeds as if none of
+    these flags were specified. This is particularly useful when compiling
+    using plugins, which usually results in the compiled modules being marked
+    as unsafe.
+
 And one general flag:
 
 .. ghc-flag:: -fpackage-trust