Handle `let { body = ... }` expressions

Nix/Parser.hs

@@ -140,10 +140,20 @@ nixPath = annotateLocation1 $ token $ fmap (mkPathF False) $ ((++)
     <?> "path"
 
 nixLet :: Parser NExprLoc
-nixLet = annotateLocation1 $ NLet
-      <$> (reserved "let" *> nixBinders)
-      <*> (whiteSpace *> reserved "in" *> nixExprLoc)
-      <?> "let"
+nixLet = annotateLocation1 $ reserved "let"
+    *> whiteSpace
+    *> (letBody <|> letBinders)
+    <?> "let block"
+  where
+    letBinders = NLet
+        <$> nixBinders
+        <*> (whiteSpace *> reserved "in" *> nixExprLoc)
+    -- Let expressions `let {..., body = ...}' are just desugared
+    -- into `(rec {..., body = ...}).body'.
+    letBody = (\x -> NSelect x ([StaticKey "body"]) Nothing) <$> aset
+    aset = annotateLocation1 $ NRecSet
+        <$> (braces nixBinders)
+
 
 nixIf :: Parser NExprLoc
 nixIf = annotateLocation1 $ NIf

tests/ParserTests.hs

@@ -184,6 +184,13 @@ case_simple_let = do
  where
   binds = [NamedVar (mkSelector "a") $ mkInt 4]
 
+case_let_body :: Assertion
+case_let_body = do
+  assertParseString "let { body = 1; }" letBody
+  where
+    letBody = Fix $ NSelect aset (mkSelector "body") Nothing
+    aset = Fix $ NRecSet [NamedVar (mkSelector "body") (mkInt 1)]
+
 case_nested_let :: Assertion
 case_nested_let = do
   assertParseString "let a = 4; in let b = 5; in a" $ Fix $ NLet