From 581654e4087ca3c4e15d1f0e0b521fbd4424d0d1 Mon Sep 17 00:00:00 2001
From: Andrey Semashev <andrey.semashev@gmail.com>
Date: Tue, 3 May 2022 01:05:56 +0300
Subject: [PATCH] Use assert in string_view::remove_prefix/suffix to enforce
 preconditions.

This is in line with std::string_view::remove_prefix/suffix definition, where
calling the method with n > size() is UB. We're keeping the check to clamp
n to size() for now for backward compatibility so that it can be eventually
removed.

Closes https://github.com/boostorg/utility/issues/92.
---
 include/boost/utility/string_view.hpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/boost/utility/string_view.hpp b/include/boost/utility/string_view.hpp
index cf47c10..3d195b6 100644
--- a/include/boost/utility/string_view.hpp
+++ b/include/boost/utility/string_view.hpp
@@ -23,6 +23,7 @@
 #include <boost/io/ostream_put.hpp>
 #include <boost/utility/string_view_fwd.hpp>
 #include <boost/throw_exception.hpp>
+#include <boost/assert.hpp>
 
 #include <cstddef>
 #include <stdexcept>
@@ -140,6 +141,8 @@ namespace boost {
         void clear() BOOST_NOEXCEPT { len_ = 0; }          // Boost extension
 
         BOOST_CXX14_CONSTEXPR void remove_prefix(size_type n) {
+            BOOST_ASSERT(n <= size());
+            // This check is deprecated and is left for backward compatibility. It will be removed in the future.
             if ( n > len_ )
                 n = len_;
             ptr_ += n;
@@ -147,6 +150,8 @@ namespace boost {
             }
 
         BOOST_CXX14_CONSTEXPR void remove_suffix(size_type n) {
+            BOOST_ASSERT(n <= size());
+            // This check is deprecated and is left for backward compatibility. It will be removed in the future.
             if ( n > len_ )
                 n = len_;
             len_ -= n;