fix: align %p behavior with native C Lua

src/Lua/Standard/Internal/MatchState.cs

@@ -460,7 +460,13 @@ static bool MatchClass(char c, char cl)
                 res = char.IsLower(c);
                 break;
             case 'p':
-                res = char.IsPunctuation(c);
+                // Emulate C ispunct; .NET's char.IsPunctuation does not include symbols like '='.
+                res =
+                    c
+                        is (>= '!' and <= '/')
+                            or (>= ':' and <= '@')
+                            or (>= '[' and <= '`')
+                            or (>= '{' and <= '~');
                 break;
             case 's':
                 res = char.IsWhiteSpace(c);

tests/Lua.Tests/PatternMatchingTests.cs

@@ -597,6 +597,50 @@ public async Task Test_StringGSub_PatternReplacements()
         Assert.That(result[1].Read<double>(), Is.EqualTo(1));
     }
 
+    [Test]
+    public async Task Test_StringGSub_PunctuationClassCapturesAsciiSymbolCharacters()
+    {
+        var state = LuaState.Create();
+        state.OpenStringLibrary();
+
+        var result = await state.DoStringAsync(
+            """
+            local punctuation = [=[!"#$%&'()*+,-./
+            :;<=>?@
+            [\]^_`
+            {|}~]=]
+            local matched = ''
+            local count = 0
+            string.gsub(punctuation, '%p', function(c)
+                matched = matched .. c
+                count = count + 1
+            end)
+            return matched, count
+            """
+        );
+
+        Assert.That(result[0].Read<string>(), Is.EqualTo("!\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~"));
+        Assert.That(result[1].Read<double>(), Is.EqualTo(32));
+
+        // Lua %p does not capture non-ASCII punctuation characters
+        result = await state.DoStringAsync(
+            """
+            local text = '’،。、！？'
+            return string.gsub(text, '%p', 'X')
+            """
+        );
+
+        Assert.That(result[0].Read<string>(), Is.EqualTo("’،。、！？"));
+        Assert.That(result[1].Read<double>(), Is.EqualTo(0));
+
+        result = await state.DoStringAsync(
+            "return string.gsub('abc=xyz', '(%w*)(%p)(%w+)', '%3%2%1-%0')"
+        );
+
+        Assert.That(result[0].Read<string>(), Is.EqualTo("xyz=abc-abc=xyz"));
+        Assert.That(result[1].Read<double>(), Is.EqualTo(1));
+    }
+
     [Test]
     public async Task Test_StringGSub_FunctionReplacements()
     {