Merge pull request #2926 from Alex1005a/let-in-do

Add explicit error when using let-in in do block

src/Idris/Parser.idr

@@ -922,7 +922,10 @@ mutual
     <|> do decoratedKeyword fname "let"
            commit
            res <- nonEmptyBlock (letBlock fname)
-           atEnd indents
+           do b <- bounds (decoratedKeyword fname "in")
+              fatalLoc {c = True} b.bounds "Let-in not supported in do block. Did you mean (let ... in ...)?"
+             <|>
+           do atEnd indents
               pure (mkDoLets fname res)
     <|> do b <- bounds (decoratedKeyword fname "rewrite" *> expr pdef fname indents)
            atEnd indents

tests/Main.idr

@@ -96,7 +96,7 @@ idrisTestsError = MkTestPool "Error messages" [] Nothing
        "perror011", "perror012", "perror013", "perror014", "perror015",
        "perror016", "perror017", "perror018", "perror019", "perror020",
        "perror021", "perror022", "perror023", "perror024", "perror025",
-       "perror026", "perror027"]
+       "perror026", "perror027", "perror028"]
 
 idrisTestsInteractive : TestPool
 idrisTestsInteractive = MkTestPool "Interactive editing" [] Nothing

tests/idris2/perror028/LetInDo.idr

@@ -0,0 +1,6 @@
+module LetInDo
+
+letInDo : Monad m => m Int
+letInDo = do
+  y <- pure 10
+  let x = 5 in pure $ y + x

tests/idris2/perror028/expected

@@ -0,0 +1,11 @@
+1/1: Building LetInDo (LetInDo.idr)
+Error: Let-in not supported in do block. Did you mean (let ... in ...)?.
+
+LetInDo:6:13--6:15
+ 2 | 
+ 3 | letInDo : Monad m => m Int
+ 4 | letInDo = do
+ 5 |   y <- pure 10
+ 6 |   let x = 5 in pure $ y + x
+                 ^^
+

tests/idris2/perror028/run

@@ -0,0 +1,3 @@
+rm -rf build
+
+$1 --no-color --console-width 0 --check LetInDo.idr