Add support for triple quoted ASCII byte string (#19182)

Author: kerams

docs/release-notes/.FSharp.Compiler.Service/11.0.0.md

@@ -21,6 +21,7 @@
 * Type checker: recover on checking binding parameter constraints ([#19046](https://github.com/dotnet/fsharp/pull/19046))
 * Debugger: provide breakpoint ranges for short lambdas ([#19067](https://github.com/dotnet/fsharp/pull/19067))
 * FSharpDiagnostic: add default severity ([#19152](https://github.com/dotnet/fsharp/pull/19152))
+* Add support for triple quoted ASCII byte string ([#19182](https://github.com/dotnet/fsharp/pull/19182))
 
 ### Changed
 

src/Compiler/lex.fsl

@@ -1502,6 +1502,12 @@ and tripleQuoteString (sargs: LexerStringArgs) (skip: bool) = parse
       let cont = LexCont.Token(args.ifdefStack, args.stringNest)
       fin.Finish buf kind LexerStringFinisherContext.TripleQuote cont }
 
+ |  '"' '"' '"' 'B'
+    { let (buf, fin, _m, kind, args) = sargs
+      args.interpolationDelimiterLength <- 0
+      let cont = LexCont.Token(args.ifdefStack, args.stringNest)
+      fin.Finish buf { kind with IsByteString = true } LexerStringFinisherContext.TripleQuote cont }
+
  | newline
     { let (buf, _fin, m, kind, args) = sargs
       incrLine lexbuf

tests/fsharp/Compiler/Conformance/BasicGrammarElements/BasicConstants.fs

@@ -9,8 +9,10 @@ module ``Basic Grammar Element Constants`` =
 
     [<Fact>]
     let ``Basic constants compile `` () =
+        let tripleQuotedByteString = " \"\"\" \" \"\"\"B "
+
         CompilerAssert.Pass 
-            """
+            $"""
 let sbyteConst = 1y
 let int16Const = 1us
 let int32Const = 1ul
@@ -42,6 +44,8 @@ let charConst = '1'
 let stringConst = "1"
     
 let bytestringConst = "1"B
+
+let byteTripleQuotedStringConst = {tripleQuotedByteString}
     
 let bytecharConst = '1'B