Add range checks for character classes.

src/Workspaces/Core/Portable/RegularExpressions/RegexParser.cs

@@ -1046,6 +1046,15 @@ private void ParseCharacterClassComponents(ArrayBuilder<RegexExpressionNode> com
                 {
                     var right = ParseCharacterClassComponentPiece(isFirst: false, afterRangeMinus: true);
 
+                    if (TryGetRangeComponentValue(left, out var leftCh) &&
+                        TryGetRangeComponentValue(right, out var rightCh) &&
+                        leftCh > rightCh)
+                    {
+                        minusToken = minusToken.AddDiagnosticIfNone(new RegexDiagnostic(
+                            WorkspacesResources.x_y_range_in_reverse_order,
+                            GetSpan(minusToken)));
+                    }
+
                     components.Add(new RegexCharacterClassRangeNode(left, minusToken, right));
                 }
             }
@@ -1055,6 +1064,131 @@ private void ParseCharacterClassComponents(ArrayBuilder<RegexExpressionNode> com
             }
         }
 
+        private bool TryGetRangeComponentValue(RegexPrimaryExpressionNode component, out char ch)
+        {
+            // Don't bother examining the component if it has any errors already.  This also means
+            // we don't have to worry about running into invalid escape sequences and the like.
+            if (!HasProblem(component))
+            {
+                return TryGetRangeComponentValueWorker(component, out ch);
+            }
+
+            ch = default;
+            return false;
+        }
+
+        private bool TryGetRangeComponentValueWorker(RegexPrimaryExpressionNode component, out char ch)
+        {
+            switch (component.Kind)
+            {
+                case RegexKind.SimpleEscape:
+                    ch = ((RegexSimpleEscapeNode)component).TypeToken.VirtualChars[0];
+                    return true;
+
+                case RegexKind.ControlEscape:
+                    var controlEscape = (RegexControlEscapeNode)component;
+                    var controlCh = controlEscape.TypeToken.VirtualChars[0].Char;
+                    ch = (char)(controlCh - '@');
+                    return true;
+
+                case RegexKind.OctalEscape:
+                    ch = GetCharValue(((RegexOctalEscapeNode)component).OctalText, withBase: 8);
+                    return true;
+
+                case RegexKind.HexEscape:
+                    ch = GetCharValue(((RegexHexEscapeNode)component).HexText, withBase: 16);
+                    return true;
+
+                case RegexKind.UnicodeEscape:
+                    ch = GetCharValue(((RegexUnicodeEscapeNode)component).HexText, withBase: 16);
+                    return true;
+
+                case RegexKind.PosixProperty:
+                    // When the native parser sees [:...:] it treats this as if it just saw '[' and skipped the 
+                    // rest.
+                    ch = '[';
+                    return true;
+
+                case RegexKind.Text:
+                    ch = ((RegexTextNode)component).TextToken.VirtualChars[0];
+                    return true;
+            }
+
+            ch = default;
+            return false;
+        }
+
+        private char GetCharValue(RegexToken hexText, int withBase)
+        {
+            var total = 0;
+            foreach (var vc in hexText.VirtualChars)
+            {
+                total *= withBase;
+                total += HexValue(vc.Char);
+            }
+
+            return (char)total;
+        }
+
+        private int HexValue(char ch)
+        {
+            unchecked
+            {
+                var temp = (uint)(ch - '0');
+                if (temp <= 9)
+                {
+                    return (int)temp;
+                }
+
+                temp = (uint)(ch - 'a');
+                if (temp <= 5)
+                {
+                    return (int)(temp + 10);
+                }
+
+                temp = (uint)(ch - 'A');
+                if (temp <= 5)
+                {
+                    return (int)(temp + 10);
+                }
+            }
+
+            throw new InvalidOperationException();
+        }
+
+        private bool HasProblem(RegexNodeOrToken component)
+        {
+            if (component.IsNode)
+            {
+                foreach (var child in component.Node)
+                {
+                    if (HasProblem(child))
+                    {
+                        return true;
+                    }
+                }
+            }
+            else
+            {
+                var token = component.Token;
+                if (token.IsMissing ||
+                    token.Diagnostics.Length > 0)
+                {
+                    return true;
+                }
+
+                foreach (var trivia in token.LeadingTrivia)
+                {
+                    if (trivia.Diagnostics.Length > 0)
+                    {
+                        return true;
+                    }
+                }
+            }
+
+            return false;
+        }
+
         private RegexPrimaryExpressionNode ParseCharacterClassComponentPiece(bool isFirst, bool afterRangeMinus)
         {
             if (_currentToken.Kind == RegexKind.BackslashToken && _lexer.Position < _lexer.Text.Length)

src/Workspaces/Core/Portable/WorkspacesResources.Designer.cs

@@ -1763,5 +1763,14 @@ internal class WorkspacesResources {
                 return ResourceManager.GetString("Workspace_is_not_empty", resourceCulture);
             }
         }
+        
+        /// <summary>
+        ///   Looks up a localized string similar to [x-y] range in reverse order.
+        /// </summary>
+        internal static string x_y_range_in_reverse_order {
+            get {
+                return ResourceManager.GetString("x_y_range_in_reverse_order", resourceCulture);
+            }
+        }
     }
 }

src/Workspaces/Core/Portable/WorkspacesResources.resx

@@ -703,4 +703,7 @@
   <data name="Unterminated_regex_comment" xml:space="preserve">
     <value>Unterminated (?#...) comment</value>
   </data>
+  <data name="x_y_range_in_reverse_order" xml:space="preserve">
+    <value>[x-y] range in reverse order</value>
+  </data>
 </root>
\ No newline at end of file

src/Workspaces/Core/Portable/xlf/WorkspacesResources.cs.xlf

@@ -947,6 +947,11 @@
         <target state="new">Unterminated (?#...) comment</target>
         <note />
       </trans-unit>
+      <trans-unit id="x_y_range_in_reverse_order">
+        <source>[x-y] range in reverse order</source>
+        <target state="new">[x-y] range in reverse order</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/Workspaces/Core/Portable/xlf/WorkspacesResources.de.xlf

@@ -947,6 +947,11 @@
         <target state="new">Unterminated (?#...) comment</target>
         <note />
       </trans-unit>
+      <trans-unit id="x_y_range_in_reverse_order">
+        <source>[x-y] range in reverse order</source>
+        <target state="new">[x-y] range in reverse order</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/Workspaces/Core/Portable/xlf/WorkspacesResources.es.xlf

@@ -947,6 +947,11 @@
         <target state="new">Unterminated (?#...) comment</target>
         <note />
       </trans-unit>
+      <trans-unit id="x_y_range_in_reverse_order">
+        <source>[x-y] range in reverse order</source>
+        <target state="new">[x-y] range in reverse order</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/Workspaces/Core/Portable/xlf/WorkspacesResources.fr.xlf

@@ -947,6 +947,11 @@
         <target state="new">Unterminated (?#...) comment</target>
         <note />
       </trans-unit>
+      <trans-unit id="x_y_range_in_reverse_order">
+        <source>[x-y] range in reverse order</source>
+        <target state="new">[x-y] range in reverse order</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/Workspaces/Core/Portable/xlf/WorkspacesResources.it.xlf

@@ -947,6 +947,11 @@
         <target state="new">Unterminated (?#...) comment</target>
         <note />
       </trans-unit>
+      <trans-unit id="x_y_range_in_reverse_order">
+        <source>[x-y] range in reverse order</source>
+        <target state="new">[x-y] range in reverse order</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/Workspaces/Core/Portable/xlf/WorkspacesResources.ja.xlf

@@ -947,6 +947,11 @@
         <target state="new">Unterminated (?#...) comment</target>
         <note />
       </trans-unit>
+      <trans-unit id="x_y_range_in_reverse_order">
+        <source>[x-y] range in reverse order</source>
+        <target state="new">[x-y] range in reverse order</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/Workspaces/Core/Portable/xlf/WorkspacesResources.ko.xlf

@@ -947,6 +947,11 @@
         <target state="new">Unterminated (?#...) comment</target>
         <note />
       </trans-unit>
+      <trans-unit id="x_y_range_in_reverse_order">
+        <source>[x-y] range in reverse order</source>
+        <target state="new">[x-y] range in reverse order</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/Workspaces/Core/Portable/xlf/WorkspacesResources.pl.xlf

@@ -947,6 +947,11 @@
         <target state="new">Unterminated (?#...) comment</target>
         <note />
       </trans-unit>
+      <trans-unit id="x_y_range_in_reverse_order">
+        <source>[x-y] range in reverse order</source>
+        <target state="new">[x-y] range in reverse order</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/Workspaces/Core/Portable/xlf/WorkspacesResources.pt-BR.xlf

@@ -947,6 +947,11 @@
         <target state="new">Unterminated (?#...) comment</target>
         <note />
       </trans-unit>
+      <trans-unit id="x_y_range_in_reverse_order">
+        <source>[x-y] range in reverse order</source>
+        <target state="new">[x-y] range in reverse order</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/Workspaces/Core/Portable/xlf/WorkspacesResources.ru.xlf

@@ -947,6 +947,11 @@
         <target state="new">Unterminated (?#...) comment</target>
         <note />
       </trans-unit>
+      <trans-unit id="x_y_range_in_reverse_order">
+        <source>[x-y] range in reverse order</source>
+        <target state="new">[x-y] range in reverse order</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/Workspaces/Core/Portable/xlf/WorkspacesResources.tr.xlf

@@ -947,6 +947,11 @@
         <target state="new">Unterminated (?#...) comment</target>
         <note />
       </trans-unit>
+      <trans-unit id="x_y_range_in_reverse_order">
+        <source>[x-y] range in reverse order</source>
+        <target state="new">[x-y] range in reverse order</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/Workspaces/Core/Portable/xlf/WorkspacesResources.zh-Hans.xlf

@@ -947,6 +947,11 @@
         <target state="new">Unterminated (?#...) comment</target>
         <note />
       </trans-unit>
+      <trans-unit id="x_y_range_in_reverse_order">
+        <source>[x-y] range in reverse order</source>
+        <target state="new">[x-y] range in reverse order</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file

src/Workspaces/Core/Portable/xlf/WorkspacesResources.zh-Hant.xlf

@@ -947,6 +947,11 @@
         <target state="new">Unterminated (?#...) comment</target>
         <note />
       </trans-unit>
+      <trans-unit id="x_y_range_in_reverse_order">
+        <source>[x-y] range in reverse order</source>
+        <target state="new">[x-y] range in reverse order</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>
\ No newline at end of file