In the route syntax, allow trailing backslashes to indicate line continuation.

yesod-core/Yesod/Routes/Parse.hs

@@ -65,7 +65,7 @@ parseRoutesNoCheck = QuasiQuoter
 -- invalid input.
 resourcesFromString :: String -> [ResourceTree String]
 resourcesFromString =
-    fst . parse 0 . filter (not . all (== ' ')) . lines . filter (/= '\r')
+    fst . parse 0 . filter (not . all (== ' ')) . foldr lineContinuations [] . lines . filter (/= '\r')
   where
     parse _ [] = ([], [])
     parse indent (thisLine:otherLines)
@@ -285,3 +285,10 @@ dropBracket str@('{':x) = case break (== '}') x of
     _ -> error $ "Unclosed bracket ('{'): " ++ str
 dropBracket x = x
 
+-- If this line ends with a backslash, concatenate it together with the next line.
+lineContinuations :: String -> [String] -> [String]
+lineContinuations this [] = [this]
+lineContinuations this below@(next:rest) = case unsnoc this of
+    Just (this', '\\') -> (this'++next):rest
+    _ -> this:below
+  where unsnoc s = if null s then Nothing else Just (init s, last s)

yesod-core/test/RouteSpec.hs

@@ -17,7 +17,7 @@ import Test.HUnit ((@?=))
 import Data.Text (Text, pack, unpack, singleton)
 import Yesod.Routes.Class hiding (Route)
 import qualified Yesod.Routes.Class as YRC
-import Yesod.Routes.Parse (parseRoutesNoCheck, parseTypeTree, TypeTree (..))
+import Yesod.Routes.Parse (parseRoutesFile, parseRoutesNoCheck, parseTypeTree, TypeTree (..))
 import Yesod.Routes.Overlap (findOverlapNames)
 import Yesod.Routes.TH hiding (Dispatch)
 import Language.Haskell.TH.Syntax
@@ -219,11 +219,17 @@ main = hspec $ do
         it "routes to subparam" $ disp "PUT" ["subparam", "6", "q"]
             @?= (pack "subparam 6 q", Just $ SubparamR 6 $ ParamRoute 'q')
 
-    describe "parsing" $ do
+    describe "route parsing" $ do
         it "subsites work" $ do
             parseRoute ([pack "subsite", pack "foo"], [(pack "bar", pack "baz")]) @?=
                 Just (SubsiteR $ MySubRoute ([pack "foo"], [(pack "bar", pack "baz")]))
 
+    describe "routing table parsing" $ do
+        it "recognizes trailing backslashes as line continuation directives" $ do
+            let routes :: [ResourceTree String]
+                routes = $(parseRoutesFile "test/fixtures/routes_with_line_continuations")
+            length routes @?= 3
+
     describe "overlap checking" $ do
         it "catches overlapping statics" $ do
             let routes :: [ResourceTree String]

yesod-core/test/fixtures/routes_with_line_continuations

@@ -0,0 +1,11 @@
+-- This fixture to test line continuations is in a separate file
+-- because when I put it in an in-line quasi-quotation, the compiler
+-- performed the line continuations processing itself.
+
+/foo1 \
+    Foo1
+/foo2 Foo2
+/foo3 \
+    Foo3 \
+    GET POST \
+    !foo