refactor: simplify IsLatinLetter range test, document broad catch

csharp/PhoneNumbers.MetadataBuilder/Program.cs

@@ -57,6 +57,12 @@ public static int Main(string[] args)
             try { return Run(args); }
             finally { mutex.ReleaseMutex(); }
         }
+        // Deliberately broad: this is the process-wide handler for a build-time tool, and the
+        // work it guards reaches XML parsing, file I/O and named-mutex code that between them
+        // can throw a dozen unrelated types. Nothing is swallowed — the full exception goes to
+        // stderr and the non-zero exit code fails the MSBuild target that invoked us — so
+        // narrowing this would only trade a readable one-line diagnostic for an unhandled-
+        // exception crash dump, with no change to whether the build fails.
         catch (Exception ex)
         {
             Console.Error.WriteLine($"PhoneNumbers.MetadataBuilder failed: {ex.Message}");

csharp/PhoneNumbers.Test/TestPhoneNumberMatcher.cs

@@ -247,6 +247,11 @@ public void TestIsLatinLetter()
             Assert.True(PhoneNumberMatcher.IsLatinLetter('C'));
             Assert.True(PhoneNumberMatcher.IsLatinLetter('\u00C9'));
             Assert.True(PhoneNumberMatcher.IsLatinLetter('\u0301'));  // Combining acute accent
+            // One letter from each remaining accepted block, so every arm of the range test is
+            // exercised: these were the blocks no assertion reached.
+            Assert.True(PhoneNumberMatcher.IsLatinLetter('\u0100'));  // Latin Extended-A
+            Assert.True(PhoneNumberMatcher.IsLatinLetter('\u0180'));  // Latin Extended-B
+            Assert.True(PhoneNumberMatcher.IsLatinLetter('\u1E00'));  // Latin Extended Additional
             // Punctuation, digits and white-space are not considered "latin letters".
             Assert.False(PhoneNumberMatcher.IsLatinLetter(':'));
             Assert.False(PhoneNumberMatcher.IsLatinLetter('5'));

csharp/PhoneNumbers/PhoneNumberMatcher.cs

@@ -217,14 +217,15 @@ public static bool IsLatinLetter(char letter)
             // Combining marks are a subset of non-spacing-mark.
             if (!char.IsLetter(letter) && CharUnicodeInfo.GetUnicodeCategory(letter) != UnicodeCategory.NonSpacingMark)
                 return false;
-            return
-                letter <= 0x007F                             // BASIC_LATIN
-                || letter >= 0x0080 && letter <= 0x00FF     // LATIN_1_SUPPLEMENT
-                || letter >= 0x0100 && letter <= 0x017F     // LATIN_EXTENDED_A
-                || letter >= 0x1E00 && letter <= 0x1EFF     // LATIN_EXTENDED_ADDITIONAL
-                || letter >= 0x0180 && letter <= 0x024F     // LATIN_EXTENDED_B
-                || letter >= 0x0300 && letter <= 0x036F     // COMBINING_DIACRITICAL_MARKS
-                ;
+            // The Unicode blocks Java's isLatinLetter() accepts, expressed as the code point
+            // ranges that define them (C# has no Character.UnicodeBlock equivalent).
+            return letter is
+                <= '\u007F'                            // BASIC_LATIN
+                or (>= '\u0080' and <= '\u00FF')       // LATIN_1_SUPPLEMENT
+                or (>= '\u0100' and <= '\u017F')       // LATIN_EXTENDED_A
+                or (>= '\u1E00' and <= '\u1EFF')       // LATIN_EXTENDED_ADDITIONAL
+                or (>= '\u0180' and <= '\u024F')       // LATIN_EXTENDED_B
+                or (>= '\u0300' and <= '\u036F');      // COMBINING_DIACRITICAL_MARKS
         }
 
         private static bool IsInvalidPunctuationSymbol(char character)