Fix reentrancy issues in wxMSW wxTextCtrl max length handling code.

The changes of r75940 didn't work correctly if the handler of wxEVT_TEXT in
some text control modified a (potentially) different text control, as the same
global variable was reused with disastrous results. Avoid this by keeping a
stack of insertion lengths instead.

Using a per-control field would work too, but would be a bit wasteful as the
size of the stack will rarely be more than 1 (and never much more) and this
change can also be applied to 3.0 branch without breaking ABI.

Additionally, fix another problem in r75940 which used 0 as a special marker
for the insertion length, which result in redoing each insertion of empty
string (which is another word for Remove()) twice unnecessarily, by using -1
instead.

Closes #15980.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76193 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/textctrl.cpp

@@ -40,6 +40,7 @@
     #include "wx/wxcrtvararg.h"
 #endif
 
+#include "wx/stack.h"
 #include "wx/sysopt.h"
 
 #if wxUSE_CLIPBOARD
@@ -176,14 +177,15 @@ private:
 namespace
 {
 
-// The length of the text being currently inserted into the control.
+// This stack stores the length of the text being currently inserted into the
+// current control.
 //
-// This is used to pass information from DoWriteText() to AdjustSpaceLimit()
-// and is global as text can only be inserted into one text control at a time
-// by a single thread and this operation can only be done from the main thread
-// (and we don't want to waste space in every wxTextCtrl object for this field
-// unnecessarily).
-int gs_lenOfInsertedText = 0;
+// It is used to pass information from DoWriteText() to AdjustSpaceLimit()
+// and is global as text can only be inserted into a few text controls at a
+// time (but possibly more than into one, if wxEVT_TEXT event handler does
+// something that results in another text control update), and we don't want to
+// waste space in every wxTextCtrl object for this field unnecessarily.
+wxStack<int> gs_lenOfInsertedText;
 
 } // anonymous namespace
 
@@ -1154,29 +1156,27 @@ void wxTextCtrl::DoWriteText(const wxString& value, int flags)
         // Remember the length of the text we're inserting so that
         // AdjustSpaceLimit() could adjust the limit to be big enough for it:
         // and also signal us whether it did it by resetting it to 0.
-        gs_lenOfInsertedText = valueDos.length();
+        gs_lenOfInsertedText.push(valueDos.length());
 
         ::SendMessage(GetHwnd(), selectionOnly ? EM_REPLACESEL : WM_SETTEXT,
                       // EM_REPLACESEL takes 1 to indicate the operation should be redoable
                       selectionOnly ? 1 : 0, wxMSW_CONV_LPARAM(valueDos));
 
-        if ( !gs_lenOfInsertedText )
+        const int lenActuallyInserted = gs_lenOfInsertedText.top();
+        gs_lenOfInsertedText.pop();
+
+        if ( lenActuallyInserted == -1 )
         {
             // Text size limit has been hit and added text has been truncated.
             // But the max length has been increased by the EN_MAXTEXT message
-            // handler, which also reset gs_lenOfInsertedText to 0), so we
-            // should be able to set it successfully now if we try again.
+            // handler, which also reset the top of the lengths stack to -1),
+            // so we should be able to set it successfully now if we try again.
             if ( selectionOnly )
                 Undo();
 
             ::SendMessage(GetHwnd(), selectionOnly ? EM_REPLACESEL : WM_SETTEXT,
                           selectionOnly ? 1 : 0, wxMSW_CONV_LPARAM(valueDos));
         }
-        else
-        {
-            // EN_MAXTEXT handler wasn't called, so reset the flag ourselves.
-            gs_lenOfInsertedText = 0;
-        }
 
         if ( !ucf.GotUpdate() && (flags & SetValue_SendEvent) )
         {
@@ -2159,10 +2159,10 @@ bool wxTextCtrl::AdjustSpaceLimit()
         // We need to increase the size of the buffer and to avoid increasing
         // it too many times make sure that we make it at least big enough to
         // fit all the text we are currently inserting into the control.
-        unsigned long increaseBy = gs_lenOfInsertedText;
+        unsigned long increaseBy = gs_lenOfInsertedText.top();
 
-        // Don't let it affect any future unrelated calls to this function.
-        gs_lenOfInsertedText = 0;
+        // Indicate to the caller that we increased the limit.
+        gs_lenOfInsertedText.top() = -1;
 
         // But also increase it by at least 32KB chunks -- again, to avoid
         // doing it too often -- and round it up to 32KB in any case.