[committed] libstdc++: Add assertion to std::string_view::remove_suffix [PR112314]

[Jonathan Wakely]

Tested x86_64-linux. Pushed to trunk.

Backports seem reasonable.

-- >8 --

libstdc++-v3/ChangeLog:

        PR libstdc++/112314
        * include/std/string_view (string_view::remove_suffix): Add
        debug assertion.
        * 
testsuite/21_strings/basic_string_view/modifiers/remove_prefix/debug.cc:
        New test.
        * 
testsuite/21_strings/basic_string_view/modifiers/remove_suffix/debug.cc:
        New test.
---
 libstdc++-v3/include/std/string_view               |  5 ++++-
 .../modifiers/remove_prefix/debug.cc               | 14 ++++++++++++++
 .../modifiers/remove_suffix/debug.cc               | 14 ++++++++++++++
 3 files changed, 32 insertions(+), 1 deletion(-)
 create mode 100644 
libstdc++-v3/testsuite/21_strings/basic_string_view/modifiers/remove_prefix/debug.cc
 create mode 100644 
libstdc++-v3/testsuite/21_strings/basic_string_view/modifiers/remove_suffix/debug.cc

diff --git a/libstdc++-v3/include/std/string_view 
b/libstdc++-v3/include/std/string_view
index d103abda668..9deae25f712 100644
--- a/libstdc++-v3/include/std/string_view
+++ b/libstdc++-v3/include/std/string_view
@@ -301,7 +301,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       constexpr void
       remove_suffix(size_type __n) noexcept
-      { this->_M_len -= __n; }
+      {
+       __glibcxx_assert(this->_M_len >= __n);
+       this->_M_len -= __n;
+      }
 
       constexpr void
       swap(basic_string_view& __sv) noexcept
diff --git 
a/libstdc++-v3/testsuite/21_strings/basic_string_view/modifiers/remove_prefix/debug.cc
 
b/libstdc++-v3/testsuite/21_strings/basic_string_view/modifiers/remove_prefix/debug.cc
new file mode 100644
index 00000000000..37204583b71
--- /dev/null
+++ 
b/libstdc++-v3/testsuite/21_strings/basic_string_view/modifiers/remove_prefix/debug.cc
@@ -0,0 +1,14 @@
+// { dg-do compile { target c++17 } }
+
+#include <string_view>
+
+constexpr bool
+check_remove_prefix()
+{
+  std::string_view sv("123");
+  sv.remove_prefix(4);
+  // { dg-error "not a constant expression" "" { target *-*-* } 0 }
+  return true;
+}
+
+constexpr bool test = check_remove_prefix();
diff --git 
a/libstdc++-v3/testsuite/21_strings/basic_string_view/modifiers/remove_suffix/debug.cc
 
b/libstdc++-v3/testsuite/21_strings/basic_string_view/modifiers/remove_suffix/debug.cc
new file mode 100644
index 00000000000..a549e4c2471
--- /dev/null
+++ 
b/libstdc++-v3/testsuite/21_strings/basic_string_view/modifiers/remove_suffix/debug.cc
@@ -0,0 +1,14 @@
+// { dg-do compile { target c++17 } }
+
+#include <string_view>
+
+constexpr bool
+check_remove_suffix()
+{
+  std::string_view sv("123");
+  sv.remove_suffix(4);
+  // { dg-error "not a constant expression" "" { target *-*-* } 0 }
+  return true;
+}
+
+constexpr bool test = check_remove_suffix();
-- 
2.41.0