Let a regex that spans whitespace match under ByWordAny [patch]

TextFilter.Test/TextFilterTests.cs

@@ -452,6 +452,39 @@
 		Assert.IsFalse(result, "Non-matching regex should return false for ByWordAny.");
 	}
 
+	[TestMethod]
+	[DataRow("hello world", "hello world")]
+	[DataRow("hello world", @"o\sw")]
+	[DataRow("hello world", "o w")]
+	[DataRow("New York City", "New York")]
+	[DataRow("12 items left", @"\d+\s+items")]
+	public void IsMatchRegexSpanningWhitespaceMatchesUnderTheDefaults(string text, string pattern) =>
+		Assert.IsTrue(TextFilter.IsMatch(text, pattern, TextFilterType.Regex));
+
+	[TestMethod]
+	public void IsMatchRegexByWordAnyStillMatchesAWordAnchoredPattern()
+	{
+		Assert.IsTrue(TextFilter.IsMatch("hello world", "^world", TextFilterType.Regex, TextFilterMatchOptions.ByWordAny));
+		Assert.IsTrue(TextFilter.IsMatch("hello world", "hello$", TextFilterType.Regex, TextFilterMatchOptions.ByWordAny));
+		Assert.IsFalse(TextFilter.IsMatch("hello world", "hello  world", TextFilterType.Regex, TextFilterMatchOptions.ByWordAny));
+	}
+
+	[TestMethod]
+	public void FilterRegexSpanningWhitespaceKeepsMatchingItemsUnderTheDefaults()
+	{
+		List<string> strings = ["New York City", "York", "Newark"];
+		List<string> result = [.. TextFilter.Filter(strings, "New York", TextFilterType.Regex)];
+		CollectionAssert.AreEqual(new List<string> { "New York City" }, result);
+	}
+
+	[TestMethod]
+	public void DoesMatchRegexByWordAllStillRequiresEveryWordToMatchOnItsOwn()
+	{
+		// Documented: a whitespace-spanning pattern needs ByWholeString when every word must match.
+		Assert.IsFalse(TextFilter.DoesMatchRegex("hello world", "hello world", TextFilterMatchOptions.ByWordAll));
+		Assert.IsTrue(TextFilter.DoesMatchRegex("hello world", "hello world", TextFilterMatchOptions.ByWholeString));
+	}
+
 	[TestMethod]
 	public void DoesMatchRegexByWordAllReturnsFalse()
 	{

TextFilter/TextFilter.cs

@@ -124,7 +124,7 @@
 	private static readonly TimeSpan RegexMatchTimeout = TimeSpan.FromSeconds(1);
 
 	[System.Diagnostics.CodeAnalysis.SuppressMessage("Performance", "SYSLIB1045:Convert to 'GeneratedRegexAttribute'.", Justification = "Not available in older frameworks")]
 	private static Regex RegexMatchAnything() => new(".*", RegexOptions.Compiled);
 
 	/// <summary>
 	/// Gets a hint for the specified filter type.
@@ -276,7 +276,7 @@
 
 			return ExcludedTokenPrefixes.Contains(prefix)
 				? TextFilterTokenType.Excluded
 				: RequiredTokenPrefixes.Contains(prefix)
 				? TextFilterTokenType.Required
 				: TextFilterTokenType.Optional;
 		})
@@ -442,6 +442,13 @@
 	/// An invalid pattern matches everything. A pattern that cannot be evaluated within one second —
 	/// catastrophic backtracking, for instance — reports no match for the token that timed out
 	/// rather than throwing, so a caller-supplied pattern cannot hang the calling thread.
+	/// <para>
+	/// Under <see cref="TextFilterMatchOptions.ByWordAny"/> the pattern is tried against the whole text
+	/// before each word, so a pattern that spans whitespace, such as <c>New York</c> or <c>\d+\s+items</c>,
+	/// still matches. Under <see cref="TextFilterMatchOptions.ByWordAll"/> every word must match on its
+	/// own, so a pattern that spans whitespace never matches there; use
+	/// <see cref="TextFilterMatchOptions.ByWholeString"/> for those.
+	/// </para>
 	/// </remarks>
 	public static bool DoesMatchRegex(string text, string filter, TextFilterMatchOptions textFilterMatchOptions, TextFilterCaseSensitivity caseSensitivity = TextFilterCaseSensitivity.CaseSensitive)
 	{
@@ -485,24 +492,34 @@
 			return false;
 		}
 
+		// No single word contains whitespace, so a pattern like "hello world" or "o\sw" can only ever
+		// match the whole text. Under ByWordAny, try that first; the per-word pass below still runs,
+		// so a word-anchored pattern like "^world" keeps matching "hello world".
+		if (textFilterMatchOptions is TextFilterMatchOptions.ByWordAny && IsMatchWithinTimeout(regex, text))
+		{
+			return true;
+		}
+
 		Func<IEnumerable<string>, Func<string, bool>, bool> matchFunc = textFilterMatchOptions is TextFilterMatchOptions.ByWordAny
 			? Enumerable.Any
 			: Enumerable.All;
 
-		return matchFunc(textTokens, textToken =>
+		return matchFunc(textTokens, textToken => IsMatchWithinTimeout(regex, textToken));
+	}
+
+	private static bool IsMatchWithinTimeout(Regex regex, string input)
+	{
+		try
 		{
-			try
-			{
-				return regex.IsMatch(textToken);
-			}
-			catch (RegexMatchTimeoutException)
-			{
-				// A pattern that cannot be evaluated within the timeout is treated as not matching
-				// this token rather than thrown at the caller. Filtering is a predicate, and a list
-				// that throws mid-keystroke on a pathological pattern is a worse contract than one
-				// that returns nothing for it. This mirrors how an invalid pattern degrades above.
-				return false;
-			}
-		});
+			return regex.IsMatch(input);
+		}
+		catch (RegexMatchTimeoutException)
+		{
+			// A pattern that cannot be evaluated within the timeout is treated as not matching
+			// this input rather than thrown at the caller. Filtering is a predicate, and a list
+			// that throws mid-keystroke on a pathological pattern is a worse contract than one
+			// that returns nothing for it. This mirrors how an invalid pattern degrades in DoesMatchRegex.
+			return false;
+		}
 	}
 }