Fix comment handling with let-in

src-literatetests/10-tests.blt

@@ -612,6 +612,39 @@ func =
           _ -> True
       ]
 
+###############################################################################
+###############################################################################
+###############################################################################
+#group expression.let
+###############################################################################
+###############################################################################
+###############################################################################
+
+#test single-bind-comment-long
+testMethod foo bar baz qux =
+  let x = undefined foo bar baz qux qux baz bar :: String
+  -- some comment explaining the in expression
+  in  undefined foo x :: String
+
+#test single-bind-comment-short
+testMethod foo bar baz qux =
+  let x = undefined :: String
+  -- some comment explaining the in expression
+  in  undefined :: String
+
+#test single-bind-comment-before
+testMethod foo bar baz qux =
+  -- some comment explaining the in expression
+  let x = undefined :: String in undefined :: String
+
+#test multiple-binds-comment
+foo foo bar baz qux =
+  let a = 1
+      b = 2
+      c = 3
+  -- some comment explaining the in expression
+  in  undefined :: String
+
 
 ###############################################################################
 ###############################################################################

src/Language/Haskell/Brittany/Internal/Layouters/Expr.hs

@@ -727,8 +727,8 @@ layoutExpr lexpr@(L _ expr) = do
 #endif
       expDoc1     <- docSharedWrapper layoutExpr exp1
       -- We jump through some ugly hoops here to ensure proper sharing.
-      mBindDocs <- mapM (fmap (fmap return) . docWrapNodeRest lexpr . return)
-               =<< layoutLocalBinds binds
+      hasComments <- hasAnyCommentsBelow lexpr
+      mBindDocs   <- fmap (fmap (fmap pure)) $ layoutLocalBinds binds
       let
         ifIndentFreeElse :: a -> a -> a
         ifIndentFreeElse x y =
@@ -745,15 +745,17 @@ layoutExpr lexpr@(L _ expr) = do
       -- if "let" is moved horizontally as part of the transformation, as the
       -- comments before the first let item are moved horizontally with it.
       docSetBaseAndIndent $ case mBindDocs of
-        Just [bindDoc] -> docAlt
-          [ docSeq
+        Just [bindDoc] -> runFilteredAlternative $ do
+          addAlternativeCond (not hasComments) $ docSeq
             [ appSep $ docLit $ Text.pack "let"
-              , appSep $ docForceSingleline bindDoc
+            , docNodeAnnKW lexpr (Just AnnLet)
+            $ appSep $ docForceSingleline bindDoc
             , appSep $ docLit $ Text.pack "in"
             , docForceSingleline expDoc1
             ]
-          , docLines
-              [ docAlt
+          addAlternative $ docLines
+            [ docNodeAnnKW lexpr (Just AnnLet)
+            $ docAlt
                 [ docSeq
                     [ appSep $ docLit $ Text.pack "let"
                     , ifIndentFreeElse docSetBaseAndIndent docForceSingleline
@@ -775,7 +777,6 @@ layoutExpr lexpr@(L _ expr) = do
                   (docSetBaseY expDoc1)
                 ]
             ]
-          ]
         Just bindDocs@(_:_) -> runFilteredAlternative $ do
           --either
           --  let
@@ -805,7 +806,8 @@ layoutExpr lexpr@(L _ expr) = do
             IndentPolicyLeft     -> docLines noHangingBinds
             IndentPolicyMultiple -> docLines noHangingBinds
             IndentPolicyFree     -> docLines
-              [ docSeq
+              [ docNodeAnnKW lexpr (Just AnnLet)
+              $ docSeq
                 [ appSep $ docLit $ Text.pack "let"
                 , docSetBaseAndIndent $ docLines bindDocs
                 ]
@@ -816,7 +818,8 @@ layoutExpr lexpr@(L _ expr) = do
               ]
           addAlternative
             $ docLines
-            [ docAddBaseY BrIndentRegular
+            [ docNodeAnnKW lexpr (Just AnnLet)
+            $ docAddBaseY BrIndentRegular
             $ docPar
               (docLit $ Text.pack "let")
               (docSetBaseAndIndent $ docLines $ bindDocs)