Stop regex ByWordAll matching blank text

TextFilter.Test/TextFilterTests.cs

@@ -792,4 +792,30 @@
 				TextFilter.Filter(["file1.txt"], pattern, TextFilterType.Glob, TextFilterMatchOptions.ByWordAny, caseSensitivity).ToList());
 		}
 	}
+
+	[TestMethod]
+	[DataRow("", TextFilterType.Regex)]
+	[DataRow("   ", TextFilterType.Regex)]
+	[DataRow("", TextFilterType.Glob)]
+	[DataRow("   ", TextFilterType.Glob)]
+	public void ByWordAllDoesNotMatchTextWithNoWords(string text, TextFilterType filterType)
+	{
+		// Blank text splits into no words, and All over nothing is vacuously true, so the regex path
+		// used to match it against every pattern while the glob path did not. Both now agree.
+		Assert.IsFalse(TextFilter.IsMatch(text, "zzz", filterType, TextFilterMatchOptions.ByWordAll));
+		CollectionAssert.AreEqual(
+			new List<string>(),
+			TextFilter.Filter([text], "zzz", filterType, TextFilterMatchOptions.ByWordAll).ToList());
+	}
+
+	[TestMethod]
+	public void RegexByWordAllFilterDropsBlankEntries()
+	{
+		CollectionAssert.AreEqual(
+			new List<string>(),
+			TextFilter.Filter(["", "hello"], "zzz", TextFilterType.Regex, TextFilterMatchOptions.ByWordAll).ToList());
+		CollectionAssert.AreEqual(
+			new List<string> { "hello" },
+			TextFilter.Filter(["", "hello"], "hel", TextFilterType.Regex, TextFilterMatchOptions.ByWordAll).ToList());
+	}
 }

TextFilter/TextFilter.cs

@@ -123,7 +123,7 @@
 	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);
 
 	private static Glob GlobMatchAnything() => Glob.Parse("*");
 
@@ -277,7 +277,7 @@
 
 			return ExcludedTokenPrefixes.Contains(prefix)
 				? TextFilterTokenType.Excluded
 				: RequiredTokenPrefixes.Contains(prefix)
 				? TextFilterTokenType.Required
 				: TextFilterTokenType.Optional;
 		})
@@ -475,6 +475,14 @@
 			AddBounded(RegexCache, cacheKey, regex);
 		}
 
+		// Text with no words -- "" or "   " split by word -- has nothing for the pattern to match.
+		// Without this, Enumerable.All over the empty set is vacuously true, so under ByWordAll blank
+		// text matched every pattern while the glob path reported no match for the same input.
+		if (textTokens.Count == 0)
+		{
+			return false;
+		}
+
 		Func<IEnumerable<string>, Func<string, bool>, bool> matchFunc = textFilterMatchOptions is TextFilterMatchOptions.ByWordAny
 			? Enumerable.Any
 			: Enumerable.All;