Warn if unicode bidirectional formatting characters are found in the source (#20263)

1 files changed, 18 insertions, 0 deletions

diff --git a/docs/users_guide/using-warnings.rst b/docs/users_guide/using-warnings.rst
index 4cae76ec5a..8cdd5677fe 100644
--- a/docs/users_guide/using-warnings.rst
+++ b/docs/users_guide/using-warnings.rst
@@ -55,6 +55,7 @@ To reverse ``-Werror``, which makes all warnings into errors, use ``-Wwarn``.
         * :ghc-flag:`-Wstar-binder`
         * :ghc-flag:`-Woperator-whitespace-ext-conflict`
         * :ghc-flag:`-Wambiguous-fields`
+        * :ghc-flag:`-Wunicode-bidirectional-format-characters`
 
 The following flags are simple ways to select standard "packages" of warnings:
 
@@ -2169,6 +2170,23 @@ of ``-W(no-)*``.
     This warning has no effect when :extension:`DuplicateRecordFields` is
     disabled.
 
+.. ghc-flag:: -Wunicode-bidirectional-format-characters
+    :shortdesc: warn about the usage of unicode bidirectional layout override characters
+    :type: dynamic
+    :category:
+
+    Explicit unicode bidirectional formatting characters can cause source code
+    to be rendered misleadingly in many viewers. We warn if any such character
+    is present in the source.
+
+    Specifically, the characters disallowed by this warning
+    are those which are a part of the 'Explicit Formatting`
+    category of the `Unicode Bidirectional Character Type Listing
+    <https://www.unicode.org/reports/tr9/#Bidirectional_Character_Types>`_
+
+    :since: 9.0.2
+
+
 If you're feeling really paranoid, the :ghc-flag:`-dcore-lint` option is a good choice.
 It turns on heavyweight intra-pass sanity-checking within GHC. (It checks GHC's
 sanity, not yours.)