Do not cascade feature errors

src/Compilers/CSharp/Portable/Parser/Lexer.cs

@@ -932,26 +932,26 @@ private bool ScanInteger()
  return start < TextWindow.Position; 
  }
 
- // Allows underscores in integers, except at beginning and end
+ // Allows underscores in integers, except at beginning for decimal and end
  private void ScanNumericLiteralSingleInteger(ref bool underscoreInWrongPlace, ref bool usedUnderscore, bool isHex, bool isBinary)
  {
+ bool firstCharWasUnderscore = false;
  if (TextWindow.PeekChar() == '_')
  {
  if (isHex || isBinary)
  {
- CheckFeatureAvailability(MessageID.IDS_FeatureLeadingDigitSeparator);
+ firstCharWasUnderscore = true;
  }
  else
  {
  underscoreInWrongPlace = true;
  }
  }
 
- char ch;
  bool lastCharWasUnderscore = false;
  while (true)
  {
- ch = TextWindow.PeekChar();
+ char ch = TextWindow.PeekChar();
  if (ch == '_')
  {
  usedUnderscore = true;
@@ -971,10 +971,16 @@ private void ScanNumericLiteralSingleInteger(ref bool underscoreInWrongPlace, re
  TextWindow.AdvanceChar();
  }
 
- if (lastCharWasUnderscore)
+ if (lastCharWasUnderscore && !firstCharWasUnderscore)
  {
  underscoreInWrongPlace = true;
  }
+ else if (firstCharWasUnderscore)
+ {
+ CheckFeatureAvailability(MessageID.IDS_FeatureLeadingDigitSeparator);
+ // No need for cascading feature error
+ usedUnderscore = false;
+ }
  }
 
  private bool ScanNumericLiteral(ref TokenInfo info)

src/Compilers/CSharp/Test/Syntax/LexicalAndXml/LexicalTests.cs

@@ -2639,6 +2639,24 @@ public void TestNumericWithLeadingUnderscores()
  Assert.Equal(0, token.Errors().Length);
  Assert.Equal(1, token.Value);
  Assert.Equal(text, token.Text);
+
+ text = "0x__A_1L";
+ token = LexToken(text, _options72);
+
+ Assert.NotNull(token);
+ Assert.Equal(SyntaxKind.NumericLiteralToken, token.Kind());
+ Assert.Equal(0, token.Errors().Length);
+ Assert.Equal(0xA1L, token.Value);
+ Assert.Equal(text, token.Text);
+
+ text = "0b__1_1L";
+ token = LexToken(text, _options72);
+
+ Assert.NotNull(token);
+ Assert.Equal(SyntaxKind.NumericLiteralToken, token.Kind());
+ Assert.Equal(0, token.Errors().Length);
+ Assert.Equal(0b11L, token.Value);
+ Assert.Equal(text, token.Text);
  }
 
  [Fact]
@@ -2662,6 +2680,15 @@ public void TestNumericWithLeadingUnderscoresWithoutFeatureFlag()
  Assert.Equal(1, errors.Length);
  Assert.Equal((int)ErrorCode.ERR_FeatureNotAvailableInVersion7, errors[0].Code);
  Assert.Equal(text, token.Text);
+
+ text = "0x_1";
+ token = LexToken(text, _options6);
+
+ Assert.Equal(SyntaxKind.NumericLiteralToken, token.Kind());
+ errors = token.Errors();
+ Assert.Equal(1, errors.Length);
+ Assert.Equal((int)ErrorCode.ERR_FeatureNotAvailableInVersion6, errors[0].Code);
+ Assert.Equal(text, token.Text);
  }
 
  [Fact]
@@ -2766,6 +2793,17 @@ public void TestNumericWithBadUnderscores()
  Assert.Equal((int)ErrorCode.ERR_InvalidNumber, errors[0].Code);
  Assert.Equal("error CS1013: Invalid number", errors[0].ToString(EnsureEnglishUICulture.PreferredOrNull));
  Assert.Equal(text, token.Text);
+
+ text = "0x_";
+ token = LexToken(text, _options72);
+
+ Assert.NotNull(token);
+ Assert.Equal(SyntaxKind.NumericLiteralToken, token.Kind());
+ errors = token.Errors();
+ Assert.Equal(1, errors.Length);
+ Assert.Equal((int)ErrorCode.ERR_InvalidNumber, errors[0].Code);
+ Assert.Equal("error CS1013: Invalid number", errors[0].ToString(EnsureEnglishUICulture.PreferredOrNull));
+ Assert.Equal(text, token.Text);
  }
 
  [Fact]

src/Compilers/VisualBasic/Portable/Scanner/Scanner.vb

@@ -2097,17 +2097,15 @@ FullWidthRepeat2:
  result = DirectCast(result.AddError(ErrorFactory.ErrorInfo(ERRID.ERR_Overflow)), SyntaxToken)
  ElseIf UnderscoreInWrongPlace Then
  result = DirectCast(result.AddError(ErrorFactory.ErrorInfo(ERRID.ERR_Syntax)), SyntaxToken)
- End If
-
- If UnderscoreUsed Then
+ ElseIf LeadingUnderscoreUsed Then
+ result = CheckFeatureAvailability(result, Feature.LeadingDigitSeparator)
+ ElseIf UnderscoreUsed Then
  result = CheckFeatureAvailability(result, Feature.DigitSeparators)
  End If
+
  If Base = LiteralBase.Binary Then
  result = CheckFeatureAvailability(result, Feature.BinaryLiterals)
  End If
- If LeadingUnderscoreUsed Then
- result = CheckFeatureAvailability(result, Feature.LeadingDigitSeparator)
- End If
  Return result
  End Function
 

src/Compilers/VisualBasic/Test/Syntax/Scanner/ScannerTests.vb

@@ -16,6 +16,10 @@ Public Class ScannerTests
  Return SyntaxFactory.ParseToken(str, startStatement:=startStatement)
  End Function
 
+ Private Function ScanOnce(str As String, languageVersion As VisualBasic.LanguageVersion) As SyntaxToken
+ Return SyntaxFactory.ParseTokens(str, options:=New VisualBasicParseOptions(languageVersion:=languageVersion)).First()
+ End Function
+
  Private Function AsString(tokens As IEnumerable(Of SyntaxToken)) As String
  Dim str = String.Concat(From t In tokens Select t.ToFullString())
  Return str
@@ -1063,6 +1067,27 @@ End If]]>.Value,
  Assert.Equal(&O1, tk.Value)
  Assert.Equal(" &O_1 ", tk.ToFullString())
 
+ Str = " &H__1_1L "
+ tk = ScanOnce(Str)
+ Assert.Equal(SyntaxKind.IntegerLiteralToken, tk.Kind)
+ Assert.Equal(LiteralBase.Hexadecimal, tk.GetBase())
+ Assert.Equal(&H1, tk.Value)
+ Assert.Equal(" &H__1_1L ", tk.ToFullString())
+
+ Str = " &B__1_1L "
+ tk = ScanOnce(Str)
+ Assert.Equal(SyntaxKind.IntegerLiteralToken, tk.Kind)
+ Assert.Equal(LiteralBase.Binary, tk.GetBase())
+ Assert.Equal(&B11, tk.Value)
+ Assert.Equal(" &B__1_1L ", tk.ToFullString())
+
+ Str = " &O__1_1L "
+ tk = ScanOnce(Str)
+ Assert.Equal(SyntaxKind.IntegerLiteralToken, tk.Kind)
+ Assert.Equal(LiteralBase.Octal, tk.GetBase())
+ Assert.Equal(&O11, tk.Value)
+ Assert.Equal(" &O__1_1L ", tk.ToFullString())
+
  Str = " &H42L &H42& "
  Dim tks = ScanAllCheckDw(Str)
  Assert.Equal(SyntaxKind.IntegerLiteralToken, tks(0).Kind)
@@ -1265,6 +1290,25 @@ End If]]>.Value,
  Assert.Equal(SyntaxKind.FloatingLiteralToken, tk.Kind)
  Assert.Equal(30035, tk.GetSyntaxErrorsNoTree()(0).Code)
  Assert.Equal(0, CInt(tk.Value))
+
+ Str = "&H_"
+ tk = ScanOnce(Str)
+ Assert.Equal(SyntaxKind.IntegerLiteralToken, tk.Kind)
+ Dim errors = tk.Errors()
+ Assert.Equal(1, errors.Count)
+ Assert.Equal(30035, errors.First().Code)
+ Assert.Equal(0, CInt(tk.Value))
+ End Sub
+
+ <Fact>
+ Public Sub Scanner_UnderscoreFeatureFlag()
+ Dim Str = "&H_1"
+ Dim tk = ScanOnce(Str, LanguageVersion.VisualBasic14)
+ Assert.Equal(SyntaxKind.IntegerLiteralToken, tk.Kind)
+ Dim errors = tk.Errors()
+ Assert.Equal(1, errors.Count)
+ Assert.Equal(36716, errors.First().Code)
+ Assert.Equal(1, CInt(tk.Value))
  End Sub
 
  <Fact>