Fix caching wrong length in wxString(str, len) ctor in UTF-8 build.

A length greater than that of the source string could be passed to this ctor.
This worked correctly, i.e. created a string which was a copy of the source
one but cached a wrong length for it.

Avoid this by explicitly checking the length before caching it in
wxString::assign(str, len).

See #14130.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70986 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/string.h

@@ -2613,9 +2613,21 @@ public:
       return *this;
   }
 
+    // This is a non-standard-compliant overload taking the first "len"
+    // characters of the source string.
   wxString& assign(const wxString& str, size_t len)
   {
+#if wxUSE_STRING_POS_CACHE
+      // It is legal to pass len > str.length() to wxStringImpl::assign() but
+      // by restricting it here we save some work for that function so it's not
+      // really less efficient and, at the same time, ensure that we don't
+      // cache invalid length.
+      const size_t lenSrc = str.length();
+      if ( len > lenSrc )
+          len = lenSrc;
+
       wxSTRING_SET_CACHED_LENGTH(len);
+#endif // wxUSE_STRING_POS_CACHE
 
       m_impl.assign(str.m_impl, 0, str.LenToImpl(len));
 

tests/strings/strings.cpp

@@ -190,6 +190,8 @@ void StringTestCase::Constructors()
     CPPUNIT_ASSERT_EQUAL( L"Hello", wxString(L"Hello", 5) );
 #endif // wxUSE_UNICODE
 
+    CPPUNIT_ASSERT_EQUAL( 0, wxString(wxString(), 17).length() );
+
     static const char *s = "?really!";
     const char *start = wxStrchr(s, 'r');
     const char *end = wxStrchr(s, '!');