From 1921b0c043014cdcc9981eefb674f2cab3a9d72e Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <jwakely@redhat.com>
Date: Fri, 15 Nov 2024 22:03:20 +0000
Subject: [PATCH] libstdc++: Add debug assertions to std::list and
 std::forward_list

While working on fancy pointer support for the linked lists I noticed
they didn't have any debug assertions. This adds the obvious non-empty
assertions to front() and back().

libstdc++-v3/ChangeLog:

	* include/bits/forward_list.h (forward_list::front): Add
	non-empty assertions.
	* include/bits/stl_list.h (list::front, list::back): Add
	non-empty assertions.

(cherry picked from commit e7aa614d7372b5d3cbcd2400838c80ef905ba381)
---
 libstdc++-v3/include/bits/forward_list.h |  3 +++
 libstdc++-v3/include/bits/stl_list.h     | 13 +++++++++++--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/bits/forward_list.h b/libstdc++-v3/include/bits/forward_list.h
index 5ab2253f6093..1dae56c4734e 100644
--- a/libstdc++-v3/include/bits/forward_list.h
+++ b/libstdc++-v3/include/bits/forward_list.h
@@ -40,6 +40,7 @@
 #include <bits/allocator.h>
 #include <ext/alloc_traits.h>
 #include <ext/aligned_buffer.h>
+#include <debug/assertions.h>
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
@@ -821,6 +822,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       reference
       front()
       {
+	__glibcxx_requires_nonempty();
 	_Node* __front = static_cast<_Node*>(this->_M_impl._M_head._M_next);
 	return *__front->_M_valptr();
       }
@@ -833,6 +835,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       const_reference
       front() const
       {
+	__glibcxx_requires_nonempty();
 	_Node* __front = static_cast<_Node*>(this->_M_impl._M_head._M_next);
 	return *__front->_M_valptr();
       }
diff --git a/libstdc++-v3/include/bits/stl_list.h b/libstdc++-v3/include/bits/stl_list.h
index 8b2521960a8f..089484844684 100644
--- a/libstdc++-v3/include/bits/stl_list.h
+++ b/libstdc++-v3/include/bits/stl_list.h
@@ -59,6 +59,7 @@
 
 #include <bits/concept_check.h>
 #include <ext/alloc_traits.h>
+#include <debug/assertions.h>
 #if __cplusplus >= 201103L
 #include <initializer_list>
 #include <bits/allocated_ptr.h>
@@ -1203,7 +1204,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       _GLIBCXX_NODISCARD
       reference
       front() _GLIBCXX_NOEXCEPT
-      { return *begin(); }
+      {
+	__glibcxx_requires_nonempty();
+	return *begin();
+      }
 
       /**
        *  Returns a read-only (constant) reference to the data at the first
@@ -1212,7 +1216,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       _GLIBCXX_NODISCARD
       const_reference
       front() const _GLIBCXX_NOEXCEPT
-      { return *begin(); }
+      {
+	__glibcxx_requires_nonempty();
+	return *begin();
+      }
 
       /**
        *  Returns a read/write reference to the data at the last element
@@ -1222,6 +1229,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       reference
       back() _GLIBCXX_NOEXCEPT
       {
+	__glibcxx_requires_nonempty();
 	iterator __tmp = end();
 	--__tmp;
 	return *__tmp;
@@ -1235,6 +1243,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       const_reference
       back() const _GLIBCXX_NOEXCEPT
       {
+	__glibcxx_requires_nonempty();
 	const_iterator __tmp = end();
 	--__tmp;
 	return *__tmp;
-- 
2.47.2