Fix undefined behavior for good

(Where the range of values of LineEnd is [0, 2], see include/tools/lineend.hxx.)
7786bafdb8951aa3f0acda801ddb3704c81d00d8 "workaround
-Wenum-constexpr-conversion" had silenced the (unintended, see below) warning
about undefined behavior when eEnd was compared against LineEnd(-1), but failed
to address the undefined behavior when eEnd was initialized with LineEnd(-1).

(On Clang 16 trunk, the original
<https://github.com/llvm/llvm-project/commit/b3645353041818f61e2580635409ddb81ff5a272>
"[Clang] Diagnose ill-formed constant expression when setting a non fixed enum
to a value outside the range of the enumeration values" only emitted diagnostics
in constant evaluation contexts, then
<https://github.com/llvm/llvm-project/commit/cc104113ddecbdcec2cca848adbb6afa1214e9de>
"[Clang] Allow downgrading to a warning the diagnostic for setting a non fixed
enum to a value outside the range of the enumeration values" accidentally
extended that to other contexts, so caused the unintended warning here, and
finally
<https://github.com/llvm/llvm-project/commit/4e458765aaef7988e687e190d865f331727825c0>
"[Clang] Restrict non fixed enum to a value outside the range of the enumeration
values warning to context requiring a constant expression" fixed that mistake
and made the unintended warning go away again.)

Change-Id: I44c14ed9c9455d05d80baddcb63be97d0bfb0278
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/138385
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

1 files changed, 6 insertions, 4 deletions

diff --git a/sw/source/ui/dialog/ascfldlg.cxx b/sw/source/ui/dialog/ascfldlg.cxx
index 036159ec1aaa..6975cc72df8c 100644
--- a/sw/source/ui/dialog/ascfldlg.cxx
+++ b/sw/source/ui/dialog/ascfldlg.cxx
@@ -19,6 +19,7 @@
 
 #include <sal/config.h>
 
+#include <optional>
 #include <utility>
 
 #include <hintids.hxx>
@@ -364,7 +365,8 @@ void SwAsciiFilterDlg::UpdateIncludeBOMSensitiveState()
 
 IMPL_LINK_NOARG(SwAsciiFilterDlg, CharSetSelHdl, weld::ComboBox&, void)
 {
-    LineEnd eOldEnd = GetCRLF(), eEnd = LineEnd(-1);
+    LineEnd eOldEnd = GetCRLF();
+    std::optional<LineEnd> eEnd;
     LanguageType nLng = m_xFontLB->get_visible()
                     ? m_xLanguageLB->get_active_id()
                     : LANGUAGE_SYSTEM,
@@ -418,10 +420,10 @@ IMPL_LINK_NOARG(SwAsciiFilterDlg, CharSetSelHdl, weld::ComboBox&, void)
     }
 
     m_bSaveLineStatus = false;
-    if( static_cast<int>(eEnd) != -1 )       // changed?
+    if( eEnd )       // changed?
     {
-        if( eOldEnd != eEnd )
-            SetCRLF( eEnd );
+        if( eOldEnd != *eEnd )
+            SetCRLF( *eEnd );
     }
     else
     {