Add -Wmissing-safe-haskell-mode warning

2 files changed, 27 insertions, 1 deletions

diff --git a/compiler/main/HscMain.hs b/compiler/main/HscMain.hs
index 91a1f1d1e6..aa29554e9d 100644
--- a/compiler/main/HscMain.hs
+++ b/compiler/main/HscMain.hs
@@ -498,6 +498,14 @@ tcRnModule' sum save_rn_syntax mod = do
     hsc_env <- getHscEnv
     dflags   <- getDynFlags
 
+    -- -Wmissing-safe-haskell-mode
+    when (not (safeHaskellModeEnabled dflags)
+          && wopt Opt_WarnMissingSafeHaskellMode dflags) $
+        logWarnings $ unitBag $
+        makeIntoWarning (Reason Opt_WarnMissingSafeHaskellMode) $
+        mkPlainWarnMsg dflags (getLoc (hpm_module mod)) $
+        warnMissingSafeHaskellMode
+
     tcg_res <- {-# SCC "Typecheck-Rename" #-}
                ioMsgMaybe $
                    tcRnModule hsc_env sum
@@ -544,6 +552,8 @@ tcRnModule' sum save_rn_syntax mod = do
     errSafe t = quotes (pprMod t) <+> text "has been inferred as safe!"
     errTwthySafe t = quotes (pprMod t)
       <+> text "is marked as Trustworthy but has been inferred as safe!"
+    warnMissingSafeHaskellMode = ppr (moduleName (ms_mod sum))
+      <+> text "is missing Safe Haskell mode"
 
 -- | Convert a typechecked module to Core
 hscDesugar :: HscEnv -> ModSummary -> TcGblEnv -> IO ModGuts
diff --git a/docs/users_guide/safe_haskell.rst b/docs/users_guide/safe_haskell.rst
index af016194bf..3911b9f41d 100644
--- a/docs/users_guide/safe_haskell.rst
+++ b/docs/users_guide/safe_haskell.rst
@@ -740,7 +740,7 @@ And one general flag:
     requiring the package that ``M`` resides in be considered trusted, for ``M``
     to be considered trusted.
 
-And four warning flags:
+And five warning flags:
 
 .. ghc-flag:: -Wunsafe
     :shortdesc: warn if the module being compiled is regarded to be unsafe.
@@ -809,6 +809,22 @@ And four warning flags:
     ``B``, it will cause compilation error of ``A``.  When
     :ghc-flag:`-Winferred-safe-imports` is enabled, the compiler will emit a
     warning about this.
+    This option is off by default.
+
+.. ghc-flag:: -Wmissing-safe-haskell-mode
+    :shortdesc: warn when the Safe Haskell mode is not explicitly specified.
+    :type: dynamic
+    :reverse: -Wno-missing-safe-haskell-mode
+    :category:
+
+    :since: 8.10.1
+
+    .. index::
+       single: safe haskell mode, missing
+
+    The compiler will warn when none of  :extension:`Safe`,
+    :extension:`Trustworthy` or :extension:`Unsafe` is specified.
+    This option is off by default.
 
 .. _safe-compilation: