Speed up regex comment detector pattern.

src/Workspaces/Core/Portable/EmbeddedLanguages/RegularExpressions/LanguageServices/RegexPatternDetector.cs

@@ -43,7 +43,7 @@ internal sealed class RegexPatternDetector
         /// Option names are the values from the <see cref="RegexOptions"/> enum.
         /// </summary>
         private static readonly Regex s_languageCommentDetector =
-            new Regex(@"\blang(uage)?\s*=\s*regex(p)?\b((\s*,\s*)(?<option>[a-zA-Z]+))*",
+            new Regex(@"^((//)|(')|(/\*))\s*lang(uage)?\s*=\s*regex(p)?\b((\s*,\s*)(?<option>[a-zA-Z]+))*",
                 RegexOptions.ExplicitCapture | RegexOptions.IgnoreCase | RegexOptions.Compiled);
 
         private static readonly Dictionary<string, RegexOptions> s_nameToOption =

src/Workspaces/CoreTest/EmbeddedLanguages/RegularExpressions/LanguageServices/RegexPatternDetectorTests.cs

@@ -10,9 +10,9 @@ namespace Microsoft.CodeAnalysis.UnitTests.EmbeddedLanguages.RegularExpressions.
 {
     public class RegexPatternDetectorTests
     {
-        private void Match(string value, RegexOptions? expectedOptions = null)
+        private void Match(string value, RegexOptions? expectedOptions = null, string prefix = "//")
         {
-            var (matched, options) = RegexPatternDetector.TestAccessor.TryMatch(value);
+            var (matched, options) = RegexPatternDetector.TestAccessor.TryMatch(prefix + value);
             Assert.True(matched);
 
             if (expectedOptions != null)
@@ -21,9 +21,9 @@ private void Match(string value, RegexOptions? expectedOptions = null)
             }
         }
 
-        private void NoMatch(string value)
+        private void NoMatch(string value, string prefix = "//")
         {
-            var (matched, options) = RegexPatternDetector.TestAccessor.TryMatch(value);
+            var (matched, _) = RegexPatternDetector.TestAccessor.TryMatch(prefix + value);
             Assert.False(matched);
         }
 
@@ -33,6 +33,18 @@ public void TestSimpleForm()
             Match("lang=regex");
         }
 
+        [Fact]
+        public void TestSimpleFormVB()
+        {
+            Match("' lang=regex", prefix: "");
+        }
+
+        [Fact]
+        public void TestSimpleFormCSharpMultiLine()
+        {
+            Match("/* lang=regex", prefix: "");
+        }
+
         [Fact]
         public void TestEndingInP()
         {
@@ -96,13 +108,13 @@ public void TestNotWithWordCharAtEnd()
         [Fact]
         public void TestWithNoNWordBeforeStart1()
         {
-            Match(":lang=regex");
+            NoMatch(":lang=regex");
         }
 
         [Fact]
         public void TestWithNoNWordBeforeStart2()
         {
-            Match(": lang=regex");
+            NoMatch(": lang=regex");
         }
 
         [Fact]
@@ -152,5 +164,11 @@ public void TestInvalidOption2()
         {
             NoMatch("lang=regex,ecmascript,ignore");
         }
+
+        [Fact]
+        public void TestNotOnDocComment()
+        {
+            NoMatch("/// lang=regex,ignore", prefix: "");
+        }
     }
 }