No multiline string without newline

compiler/src/Parse/String.hs

@@ -170,7 +170,7 @@
 -- MULTI STRINGS
 
 multiString :: Ptr Word8 -> Ptr Word8 -> Row -> Col -> Ptr Word8 -> Row -> Col -> StringResult
 multiString pos end row col initialPos sr sc =
   if pos >= end
     then Err sr sc E.StringEndless_Multi
     else
@@ -179,7 +179,7 @@
             then
               let !pos1 = plusPtr pos 1
                in countLeadingWhiteSpaceThenMultiString 0 pos1 end (row + 1) 1 pos1 sr sc
-            else countLeadingWhiteSpaceThenMultiString 0 pos end row col initialPos sr sc
+            else Err sr sc E.StringMultilineWithoutLeadingNewline
 
 countLeadingWhiteSpaceThenMultiString :: Int -> Ptr Word8 -> Ptr Word8 -> Row -> Col -> Ptr Word8 -> Row -> Col -> StringResult
 countLeadingWhiteSpaceThenMultiString count pos end row col initialPos sr sc =

compiler/src/Reporting/Error/Syntax.hs

@@ -196,7 +196,8 @@ data CustomType
 -- EXPRESSIONS
 
 data Expr
-  = Let Let Row Col
+  = ExpressionBadEnd Row Col
+  | Let Let Row Col
   | Case Case Row Col
   | If If Row Col
   | Parenthesized Parenthesized Row Col
@@ -440,6 +441,7 @@ data String
   = StringEndless_Single
   | StringEndless_Multi
   | StringEscape Escape
+  | StringMultilineWithoutLeadingNewline
   deriving (Show)
 
 data Escape
@@ -2597,6 +2599,8 @@ isWithin desiredNode context =
 toExprReport :: Code.Source -> Context -> Expr -> Row -> Col -> Report.Report
 toExprReport source context expr startRow startCol =
   case expr of
+    ExpressionBadEnd row col ->
+      toWeirdEndReport source row col
     Let let_ row col ->
       toLetReport source context let_ row col
     Case case_ row col ->
@@ -2948,18 +2952,7 @@ toStringReport source string row col =
                     D.toSimpleNote $
                       "For a string that spans multiple lines, you can use the multi-line string\
                       \ syntax like this:",
-                    D.dullyellow $
-                      D.indent 4 $
-                        D.vcat $
-                          [ "\"\"\"",
-                            "# Multi-line Strings",
-                            "",
-                            "- start with triple double quotes",
-                            "- write whatever you want",
-                            "- no need to escape newlines or double quotes",
-                            "- end with triple double quotes",
-                            "\"\"\""
-                          ]
+                    D.dullyellow $ D.indent 3 validMultilineStringExample
                   ]
               )
     StringEndless_Multi ->
@@ -2975,22 +2968,38 @@ toStringReport source string row col =
                   [ D.reflow "Add a \"\"\" somewhere after this to end the string.",
                     D.toSimpleNote $
                       "Here is a valid multi-line string for reference:",
-                    D.dullyellow $
-                      D.indent 4 $
-                        D.vcat $
-                          [ "\"\"\"",
-                            "# Multi-line Strings",
-                            "",
-                            "- start with triple double quotes",
-                            "- write whatever you want",
-                            "- no need to escape newlines or double quotes",
-                            "- end with triple double quotes",
-                            "\"\"\""
-                          ]
+                    D.dullyellow $ D.indent 4 validMultilineStringExample
                   ]
               )
     StringEscape escape ->
       toEscapeReport source escape row col
+    StringMultilineWithoutLeadingNewline ->
+      let region = toRegion row col
+       in Report.Report "MULTILINE STRING WITHOUT NEWLINE" region [] $
+            Code.toSnippet
+              source
+              region
+              Nothing
+              ( D.reflow "The contents of a multiline sting must start on a new line",
+                D.stack
+                  [ D.reflow "Add a \"\"\" a new line right after the opening quotes.",
+                    D.toSimpleNote "Here is a valid multi-line string for reference:",
+                    D.dullyellow $ D.indent 4 validMultilineStringExample
+                  ]
+              )
+
+validMultilineStringExample :: D.Doc
+validMultilineStringExample =
+  D.vcat
+    [ "\"\"\"",
+      "# Multi-line Strings",
+      "",
+      "- start with triple double quotes",
+      "- write whatever you want",
+      "- no need to escape newlines or double quotes",
+      "- end with triple double quotes",
+      "\"\"\""
+    ]
 
 -- ESCAPES
 

tests/Parse/MultilineStringSpec.hs

@@ -7,22 +7,27 @@ import Data.ByteString qualified as BS
 import Data.Utf8 qualified as Utf8
 import Helpers.Instances ()
 import Helpers.Parse qualified as Helpers
+import Parse.Expression qualified as Expression
 import Parse.Pattern qualified as Pattern
+import Parse.Primitives qualified as P
+import Repl (Input (Help))
+import Reporting.Error.Syntax (Expr (ExpressionBadEnd))
 import Reporting.Error.Syntax qualified as Error.Syntax
 import Test.Hspec (Spec, describe, it)
+import Test.Hspec qualified as Hspec
 
 spec :: Spec
 spec = do
   describe "Multiline String" $ do
     it "regression test" $
       parse
         "normal string"
-        "\"\"\"normal string\"\"\""
+        "\"\"\"\nnormal string\"\"\""
 
     it "mixing quotes work" $ do
       parse
         "string with \" in it"
-        "\"\"\"string with \" in it\"\"\""
+        "\"\"\"\nstring with \" in it\"\"\""
 
     it "first newline, and leading whitespace, is dropped" $ do
       parse
@@ -39,6 +44,11 @@ spec = do
         "this is\\na test"
         "\"\"\"\n   this is\n a test\n\"\"\""
 
+    it "does not allow non-newline characters on the first line" $ do
+      let isCorrectError ((Error.Syntax.String Error.Syntax.StringMultilineWithoutLeadingNewline _ _)) = True
+          isCorrectError _ = False
+      Helpers.checkParseError Expression.expression ExpressionBadEnd isCorrectError "\"\"\"this is not allowed\"\"\""
+
 parse :: String -> BS.ByteString -> IO ()
 parse expectedStr =
   let isExpectedString :: Src.Pattern_ -> Bool