Use const for constant local variables in wxWidgets headers

This avoids warnings from MSVS 2017 static analyzer when C++ core rule
set is activated.

Closes https://github.com/wxWidgets/wxWidgets/pull/819

include/wx/arrstr.h

@@ -280,9 +280,9 @@ public:
     pointer operator->() const { return m_ptr; }
     itor& operator++() { --m_ptr; return *this; }
     const itor operator++(int)
-      { reverse_iterator tmp = *this; --m_ptr; return tmp; }
+      { const reverse_iterator tmp = *this; --m_ptr; return tmp; }
     itor& operator--() { ++m_ptr; return *this; }
-    const itor operator--(int) { itor tmp = *this; ++m_ptr; return tmp; }
+    const itor operator--(int) { const itor tmp = *this; ++m_ptr; return tmp; }
     bool operator ==(const itor& it) const { return m_ptr == it.m_ptr; }
     bool operator !=(const itor& it) const { return m_ptr != it.m_ptr; }
   };
@@ -307,9 +307,9 @@ public:
     pointer operator->() const { return m_ptr; }
     itor& operator++() { --m_ptr; return *this; }
     const itor operator++(int)
-      { itor tmp = *this; --m_ptr; return tmp; }
+      { const itor tmp = *this; --m_ptr; return tmp; }
     itor& operator--() { ++m_ptr; return *this; }
-    const itor operator--(int) { itor tmp = *this; ++m_ptr; return tmp; }
+    const itor operator--(int) { const itor tmp = *this; ++m_ptr; return tmp; }
     bool operator ==(const itor& it) const { return m_ptr == it.m_ptr; }
     bool operator !=(const itor& it) const { return m_ptr != it.m_ptr; }
   };
@@ -421,7 +421,7 @@ public:
     wxString* GetStrings()
     {
         if( m_strings ) return m_strings;
-        size_t count = m_array.GetCount();
+        const size_t count = m_array.GetCount();
         m_strings = new wxString[count];
         for( size_t i = 0; i < count; ++i )
             m_strings[i] = m_array[i];

include/wx/clntdata.h

@@ -47,7 +47,7 @@ public:
         if (it == m_methods.end())
             return false;
         wxShadowObjectMethod method = it->second;
-        int ret = (*method)(window, param);
+        const int ret = (*method)(window, param);
         if (returnValue)
             *returnValue = ret;
         return true;

include/wx/event.h

@@ -972,7 +972,7 @@ public:
     // propagation level value
     int StopPropagation()
     {
-        int propagationLevel = m_propagationLevel;
+        const int propagationLevel = m_propagationLevel;
         m_propagationLevel = wxEVENT_PROPAGATE_NONE;
         return propagationLevel;
     }

include/wx/file.h

@@ -65,7 +65,7 @@ public:
 
   // assign an existing file descriptor and get it back from wxFile object
   void Attach(int lfd) { Close(); m_fd = lfd; m_lasterror = 0; }
-  int  Detach() { int fdOld = m_fd; m_fd = fd_invalid; return fdOld; }
+  int  Detach() { const int fdOld = m_fd; m_fd = fd_invalid; return fdOld; }
   int  fd() const { return m_fd; }
 
   // read/write (unbuffered)

include/wx/log.h

@@ -244,7 +244,7 @@ public:
         if ( !m_data )
             return false;
 
-        wxStringToNumHashMap::const_iterator it = m_data->numValues.find(key);
+        const wxStringToNumHashMap::const_iterator it = m_data->numValues.find(key);
         if ( it == m_data->numValues.end() )
             return false;
 
@@ -258,7 +258,7 @@ public:
         if ( !m_data )
             return false;
 
-        wxStringToStringHashMap::const_iterator it = m_data->strValues.find(key);
+        const wxStringToStringHashMap::const_iterator it = m_data->strValues.find(key);
         if ( it == m_data->strValues.end() )
             return false;
 
@@ -379,7 +379,7 @@ public:
             return EnableThreadLogging(enable);
 #endif // wxUSE_THREADS
 
-        bool doLogOld = ms_doLog;
+        const bool doLogOld = ms_doLog;
         ms_doLog = enable;
         return doLogOld;
     }

include/wx/longlong.h

@@ -1060,7 +1060,7 @@ inline wxULongLong operator+(unsigned long l, const wxULongLong& ull) { return u
 
 inline wxLongLong operator-(unsigned long l, const wxULongLong& ull)
 {
-    wxULongLong ret = wxULongLong(l) - ull;
+    const wxULongLong ret = wxULongLong(l) - ull;
     return wxLongLong((wxInt32)ret.GetHi(),ret.GetLo());
 }
 

include/wx/msw/ole/oleutils.h

@@ -38,7 +38,7 @@
 // return true if ok, false otherwise
 inline bool wxOleInitialize()
 {
-    HRESULT
+    const HRESULT
     hr = ::OleInitialize(NULL);
 
     // RPC_E_CHANGED_MODE indicates that OLE had been already initialized

include/wx/msw/private/fswatcher.h

@@ -207,7 +207,7 @@ public:
         wxCHECK_MSG( m_iocp != INVALID_HANDLE_VALUE, false, "IOCP not init" );
 
         // The special values of 0 will make GetStatus() return Status_Exit.
-        int ret = PostQueuedCompletionStatus(m_iocp, 0, 0, NULL);
+        const int ret = PostQueuedCompletionStatus(m_iocp, 0, 0, NULL);
         if (!ret)
         {
             wxLogSysError(_("Unable to post completion status"));
@@ -244,7 +244,7 @@ public:
         wxCHECK_MSG( count && watch && overlapped, Status_Error,
                      "Output parameters can't be NULL" );
 
-        int ret = GetQueuedCompletionStatus(m_iocp, count, (ULONG_PTR *)watch,
+        const int ret = GetQueuedCompletionStatus(m_iocp, count, (ULONG_PTR *)watch,
                                             overlapped, INFINITE);
         if ( ret != 0 )
         {

include/wx/string.h

@@ -994,7 +994,7 @@ public:
       // This is logically equivalent to strlen(str.mb_str()) but avoids
       // actually converting the string to multibyte and just computes the
       // length that it would have after conversion.
-      size_t ofs = wxConvLibc.FromWChar(NULL, 0, str.wc_str(), str.length());
+      const size_t ofs = wxConvLibc.FromWChar(NULL, 0, str.wc_str(), str.length());
       return ofs == wxCONV_FAILED ? 0 : static_cast<ptrdiff_t>(ofs);
   }
 
@@ -2161,17 +2161,17 @@ public:
       // searching (return starting index, or -1 if not found)
   int Find(const wxString& sub) const               // like strstr
   {
-    size_type idx = find(sub);
+    const size_type idx = find(sub);
     return (idx == npos) ? wxNOT_FOUND : (int)idx;
   }
   int Find(const char *sub) const               // like strstr
   {
-    size_type idx = find(sub);
+    const size_type idx = find(sub);
     return (idx == npos) ? wxNOT_FOUND : (int)idx;
   }
   int Find(const wchar_t *sub) const               // like strstr
   {
-    size_type idx = find(sub);
+    const size_type idx = find(sub);
     return (idx == npos) ? wxNOT_FOUND : (int)idx;
   }