Fix pasting long strings in wxTextCtrl under MSW

Adjust the length limit before pasting to ensure that all text on
clipboard will be successfully pasted, instead of only pasting the part
of it which fits.

Add a unit test checking that this works.

Closes #4646.

tests/controls/textctrltest.cpp

@@ -27,6 +27,11 @@
 #include "wx/scopeguard.h"
 #include "wx/uiaction.h"
 
+#if wxUSE_CLIPBOARD
+    #include "wx/clipbrd.h"
+    #include "wx/dataobj.h"
+#endif // wxUSE_CLIPBOARD
+
 #ifdef __WXGTK__
     #include "wx/stopwatch.h"
 #endif
@@ -1341,4 +1346,74 @@ TEST_CASE("wxTextCtrl::GetBestSize", "[wxTextCtrl][best-size]")
     CHECK( sizeVeryLong.y == sizeLong.y );
 }
 
+#if wxUSE_CLIPBOARD
+
+TEST_CASE("wxTextCtrl::LongPaste", "[wxTextCtrl][clipboard][paste]")
+{
+    long style = 0;
+
+    SECTION("Plain")
+    {
+        style = wxTE_MULTILINE;
+    }
+
+    // wxTE_RICH[2] style only makes any different under MSW, so don't bother
+    // testing it under the other platforms.
+#ifdef __WXMSW__
+    SECTION("Rich")
+    {
+        style = wxTE_MULTILINE | wxTE_RICH;
+    }
+
+    SECTION("Rich v2")
+    {
+        style = wxTE_MULTILINE | wxTE_RICH2;
+    }
+#endif // __WXMSW__
+
+    if ( !style )
+    {
+        // This can happen when explicitly selecting just a single section to
+        // execute -- this code still runs even if the corresponding section is
+        // skipped, so we have to explicitly skip it too in this case.
+        return;
+    }
+
+    wxScopedPtr<wxTextCtrl>
+        text(new wxTextCtrl(wxTheApp->GetTopWindow(), wxID_ANY, wxString(),
+                            wxDefaultPosition, wxDefaultSize, style));
+
+    // This could actually be much higher, but it makes the test proportionally
+    // slower, so use a relatively small (but still requiring more space than
+    // the default maximum length under MSW) number here.
+    const int NUM_LINES = 10000;
+
+    {
+        wxClipboardLocker lock;
+
+        // Build a longish string.
+        wxString s;
+        s.reserve(NUM_LINES*5 + 10);
+        for ( int n = 0; n < NUM_LINES; ++n )
+        {
+            s += wxString::Format("%04d\n", n);
+        }
+
+        s += "THE END";
+
+        wxTheClipboard->AddData(new wxTextDataObject(s));
+    }
+
+    text->ChangeValue("THE BEGINNING\n");
+    text->SetInsertionPointEnd();
+    text->Paste();
+
+    const int numLines = text->GetNumberOfLines();
+
+    CHECK( numLines == NUM_LINES + 2 );
+    CHECK( text->GetLineText(numLines - 1) == "THE END" );
+}
+
+#endif // wxUSE_CLIPBOARD
+
 #endif //wxUSE_TEXTCTRL