add iterator_traits to ChildInstanstiablesIterator

peckato1 · peckato1 · commit ffdaf3a90b96 · 2026-03-16T09:41:48.000+01:00
I have seen the following compile error on g++-13 when trying to use
std::find_if with ChildInstanstiablesIterator:

  [9/30] Building CXX object CMakeFiles/test_schema_node.dir/tests/schema_node.cpp.o
  FAILED: [code=1] CMakeFiles/test_schema_node.dir/tests/schema_node.cpp.o
  /usr/bin/g++-13 -DDOCTEST_CONFIG_SUPER_FAST_ASSERTS -I/home/tomas/zdrojaky/cesnet/libyang-cpp/include -I/home/tomas/zdrojaky/cesnet/libyang-cpp/build-gcc-asan -I/home/tomas/zdrojaky/cesnet/libyang-cpp/tests -I/home/tomas/zdrojaky/cesnet/libyang-cpp/src -I/home/tomas/zdrojaky/cesnet/libyang-cpp -isystem /home/tomas/zdrojaky/cesnet/build/prefixes/gcc-asan/include -Wall -Wextra -pedantic -Woverloaded-virtual -Wimplicit-fallthrough -Wsuggest-override -fsanitize=address,undefined -g -I/opt/boost1.88/include -std=gnu++23 -fvisibility=hidden -fvisibility-inlines-hidden -MD -MT CMakeFiles/test_schema_node.dir/tests/schema_node.cpp.o -MF CMakeFiles/test_schema_node.dir/tests/schema_node.cpp.o.d -o CMakeFiles/test_schema_node.dir/tests/schema_node.cpp.o -c /home/tomas/zdrojaky/cesnet/libyang-cpp/tests/schema_node.cpp
  In file included from /usr/lib/gcc/x86_64-pc-linux-gnu/13.4.1/include/c++/string:51,
                   from /usr/lib/gcc/x86_64-pc-linux-gnu/13.4.1/include/c++/stdexcept:39,
                   from /usr/lib/gcc/x86_64-pc-linux-gnu/13.4.1/include/c++/system_error:43,
                   from /usr/lib/gcc/x86_64-pc-linux-gnu/13.4.1/include/c++/bits/fs_fwd.h:35,
                   from /usr/lib/gcc/x86_64-pc-linux-gnu/13.4.1/include/c++/filesystem:48,
                   from /home/tomas/zdrojaky/cesnet/libyang-cpp/include/libyang-cpp/Context.hpp:10,
                   from /home/tomas/zdrojaky/cesnet/libyang-cpp/tests/schema_node.cpp:10:
  /usr/lib/gcc/x86_64-pc-linux-gnu/13.4.1/include/c++/bits/stl_algobase.h: In instantiation of &lsquo;constexpr _Iterator std::__find_if(_Iterator, _Iterator, _Predicate) [with _Iterator = libyang::ChildInstanstiablesIterator; _Predicate = __gnu_cxx::__ops::_Iter_pred&lt;DOCTEST_ANON_FUNC_2()::&lt;lambda(const libyang::SchemaNode&amp;)&gt; &gt;]&rsquo;:
  /usr/lib/gcc/x86_64-pc-linux-gnu/13.4.1/include/c++/bits/stl_algo.h:3923:28:   required from &lsquo;constexpr _IIter std::find_if(_IIter, _IIter, _Predicate) [with _IIter = libyang::ChildInstanstiablesIterator; _Predicate = DOCTEST_ANON_FUNC_2()::&lt;lambda(const libyang::SchemaNode&amp;)&gt;]&rsquo;
  /home/tomas/zdrojaky/cesnet/libyang-cpp/tests/schema_node.cpp:269:17:   required from here
  /usr/lib/gcc/x86_64-pc-linux-gnu/13.4.1/include/c++/bits/stl_algobase.h:2117:23: error: no matching function for call to &lsquo;__find_if(libyang::ChildInstanstiablesIterator&amp;, libyang::ChildInstanstiablesIterator&amp;, __gnu_cxx::__ops::_Iter_pred&lt;DOCTEST_ANON_FUNC_2()::&lt;lambda(const libyang::SchemaNode&amp;)&gt; &gt;&amp;, std::__iterator_traits&lt;libyang::ChildInstanstiablesIterator, void&gt;::iterator_category)&rsquo;
   2117 |       return __find_if(__first, __last, __pred,
        |              ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
   2118 |                        std::__iterator_category(__first));
        |                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  /usr/lib/gcc/x86_64-pc-linux-gnu/13.4.1/include/c++/bits/stl_algobase.h:2052:5: note: candidate: &lsquo;template&lt;class _InputIterator, class _Predicate&gt; constexpr _InputIterator std::__find_if(_InputIterator, _InputIterator, _Predicate, input_iterator_tag)&rsquo;
   2052 |     __find_if(_InputIterator __first, _InputIterator __last,
        |     ^~~~~~~~~
  /usr/lib/gcc/x86_64-pc-linux-gnu/13.4.1/include/c++/bits/stl_algobase.h:2052:5: note:   template argument deduction/substitution failed:
  /usr/lib/gcc/x86_64-pc-linux-gnu/13.4.1/include/c++/bits/stl_algobase.h:2118:48: note:   cannot convert &lsquo;std::__iterator_category&lt;libyang::ChildInstanstiablesIterator&gt;(__first)&rsquo; (type &lsquo;std::__iterator_traits&lt;libyang::ChildInstanstiablesIterator, void&gt;::iterator_category&rsquo; {aka &lsquo;std::output_iterator_tag&rsquo;}) to type &lsquo;std::input_iterator_tag&rsquo;
   2118 |                        std::__iterator_category(__first));
        |                        ~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~
  /usr/lib/gcc/x86_64-pc-linux-gnu/13.4.1/include/c++/bits/stl_algobase.h:2064:5: note: candidate: &lsquo;template&lt;class _RandomAccessIterator, class _Predicate&gt; constexpr _RandomAccessIterator std::__find_if(_RandomAccessIterator, _RandomAccessIterator, _Predicate, random_access_iterator_tag)&rsquo;
   2064 |     __find_if(_RandomAccessIterator __first, _RandomAccessIterator __last,
        |     ^~~~~~~~~
  /usr/lib/gcc/x86_64-pc-linux-gnu/13.4.1/include/c++/bits/stl_algobase.h:2064:5: note:   template argument deduction/substitution failed:
  /usr/lib/gcc/x86_64-pc-linux-gnu/13.4.1/include/c++/bits/stl_algobase.h:2118:48: note:   cannot convert &lsquo;std::__iterator_category&lt;libyang::ChildInstanstiablesIterator&gt;(__first)&rsquo; (type &lsquo;std::__iterator_traits&lt;libyang::ChildInstanstiablesIterator, void&gt;::iterator_category&rsquo; {aka &lsquo;std::output_iterator_tag&rsquo;}) to type &lsquo;std::random_access_iterator_tag&rsquo;
   2118 |                        std::__iterator_category(__first));
        |                        ~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~
  /usr/lib/gcc/x86_64-pc-linux-gnu/13.4.1/include/c++/bits/stl_algobase.h:2115:5: note: candidate: &lsquo;template&lt;class _Iterator, class _Predicate&gt; constexpr _Iterator std::__find_if(_Iterator, _Iterator, _Predicate)&rsquo;
   2115 |     __find_if(_Iterator __first, _Iterator __last, _Predicate __pred)
        |     ^~~~~~~~~
  /usr/lib/gcc/x86_64-pc-linux-gnu/13.4.1/include/c++/bits/stl_algobase.h:2115:5: note:   template argument deduction/substitution failed:
  /usr/lib/gcc/x86_64-pc-linux-gnu/13.4.1/include/c++/bits/stl_algobase.h:2117:23: note:   candidate expects 3 arguments, 4 provided
   2117 |       return __find_if(__first, __last, __pred,
        |              ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
   2118 |                        std::__iterator_category(__first));
        |                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  [21/30] Building CXX object CMakeFiles/test_data_node.dir/tests/data_node.cpp.o
  ninja: build stopped: subcommand failed.

It seems our iterator category is wrongly deduced to
std::output_iterator_tag which does not work with std::find_if.

This patch adds the necessary typedefs to ChildInstanstiablesIterator
to make it a valid input iterator.

Interestingly, I have not seen this on my clang++-21, only on CI's
g++-13.

Change-Id: I0c4503cb3bd6166f3c79037ea2c4e3bed1520042
diff --git a/include/libyang-cpp/ChildInstantiables.hpp b/include/libyang-cpp/ChildInstantiables.hpp
@@ -6,6 +6,7 @@
  * SPDX-License-Identifier: BSD-3-Clause
 */
 #pragma once
+#include <iterator>
 #include <libyang-cpp/SchemaNode.hpp>
 #include <libyang-cpp/export.h>
 
@@ -16,6 +17,11 @@ class Module;
 
 class LIBYANG_CPP_EXPORT ChildInstanstiablesIterator {
 public:
+    using iterator_category = std::input_iterator_tag;
+    using value_type = SchemaNode;
+    using reference = void;
+    using difference_type = std::ptrdiff_t;
+
     friend ChildInstanstiables;
     SchemaNode operator*() const;
     ChildInstanstiablesIterator& operator++();
diff --git a/tests/schema_node.cpp b/tests/schema_node.cpp
@@ -264,6 +264,10 @@ TEST_CASE("SchemaNode")
             }
 
             REQUIRE(expectedPaths == actualPaths);
+
+            for (const auto& path : expectedPaths) {
+                REQUIRE(std::find_if(children->begin(), children->end(), [&path](const libyang::SchemaNode& node) { return node.path() == path; }) != children->end());
+            }
         }
 
         DOCTEST_SUBCASE("unimplemented module")

Original file line number	Diff line number	Diff line change
`@@ -264,6 +264,10 @@ TEST_CASE("SchemaNode")`
`264`	`264`	`}`
`265`	`265`
`266`	`266`	`REQUIRE(expectedPaths == actualPaths);`
	`267`	`+`
	`268`	`+ for (const auto& path : expectedPaths) {`
	`269`	`+ REQUIRE(std::find_if(children->begin(), children->end(), [&path](const libyang::SchemaNode& node) { return node.path() == path; }) != children->end());`
	`270`	`+ }`
`267`	`271`	`}`
`268`	`272`
`269`	`273`	`DOCTEST_SUBCASE("unimplemented module")`