Decimal-char in String can be `> 255` and is then wrapped to be inside `0..255`

[Booksbaum]

Decimal char notation:

\DDD (where D indicates a decimal digit; range of 000 - 255; for example, \231 = "ç")

BUT: a value > 255 is accepted too -- but gets wrapped into range (% 256):

> int 'Ω';;
val it: int = 937

> "\937";;
val it: string = "©"

> int ("\937"[0]);;
val it: int = 169
> 937 % 256;;
val it: int = 169

(fable repl)

Expected behavior

Should be compiler error, like in char:

> '\937';;
  ^^^^^^
stdin(85,1): error FS1158: This is not a valid character literal

Actual behavior

Decimal > 255 is accepted and wrapped into byte range.

I think issue is here:

fsharp/src/Compiler/lex.fsl

Lines 1185 to 1192 in 443b3ab

	| trigraph
	{ let (buf, _fin, m, kind, args) = sargs
	let s = lexeme lexbuf
	addByteChar buf (trigraph s.[1] s.[2] s.[3])
	if not skip then
	STRING_TEXT (LexCont.String(args.ifdefStack, args.stringNest, LexerStringStyle.SingleQuote, kind, args.interpolationDelimiterLength, m))
	else
	singleQuoteString sargs skip lexbuf }

There's no range check and addByteChar then wraps the value to byte range

I'm going to fix this together with the other char notations issues.

Related information

• Operating system: Windows 11 x64
• dotnet --version: 7.0.307, 8.0.100-preview.7.23376.3