Warn about suspicious IFS, such as IFS="\n"

ShellCheck/Analytics.hs

@@ -197,6 +197,7 @@ nodeChecks = [
     ,checkUnsupported
     ,checkMultipleAppends
     ,checkAliasesExpandEarly
+    ,checkSuspiciousIFS
     ]
 
 
@@ -2723,3 +2724,22 @@ checkAliasesExpandEarly params =
         flip mapM_ (take 1 $ filter (not . isLiteral) $ getWordParts arg) $
             \x -> warn (getId x) 2139 "This expands when defined, not when used. Consider escaping."
     checkArg _ = return ()
+
+prop_checkSuspiciousIFS1 = verify checkSuspiciousIFS "IFS=\"\\n\""
+prop_checkSuspiciousIFS2 = verifyNot checkSuspiciousIFS "IFS=$'\\t'"
+checkSuspiciousIFS params (T_Assignment id Assign "IFS" Nothing value) =
+    potentially $ do
+        str <- getLiteralString value
+        return $ check str
+  where
+    n = if (shellType params == Sh) then "'<literal linefeed here>'" else "$'\\n'"
+    t = if (shellType params == Sh) then "\"$(printf '\\t')\"" else "$'\\t'"
+    check value =
+        case value of
+            "\\n" -> suggest n
+            "/n" -> suggest n
+            "\\t" -> suggest t
+            "/t" -> suggest t
+            _ -> return ()
+    suggest r = warn id 2141 $ "Did you mean IFS=" ++ r ++ " ?"
+checkSuspiciousIFS _ _ = return ()

ShellCheck/Parser.hs

@@ -965,10 +965,12 @@ readNormalEscaped = called "escaped char" $ do
         do
             next <- anyChar
             case escapedChar next of
-                Just name -> parseNoteAt pos WarningC 1012 $ "\\" ++ [next] ++ " is just literal '" ++ [next] ++ "' here. For " ++ name ++ ", use \"$(printf \"\\" ++ [next] ++ "\")\"."
+                Just name -> parseNoteAt pos WarningC 1012 $ "\\" ++ [next] ++ " is just literal '" ++ [next] ++ "' here. For " ++ name ++ ", use " ++ (alternative next) ++ " instead."
                 Nothing -> parseNoteAt pos InfoC 1001 $ "This \\" ++ [next] ++ " will be a regular '" ++ [next] ++ "' in this context."
             return [next]
   where
+    alternative 'n' = "a quoted, literal line feed"
+    alternative t = "\"$(printf \"\\" ++ [t] ++ "\")\""
     escapedChar 'n' = Just "line feed"
     escapedChar 't' = Just "tab"
     escapedChar 'r' = Just "carriage return"