Don't set C++ standard version in the CMake

[ednolan]

Doing so violates the [CMAKE.PASSIVE_PROJECT] requirement of the Beman Standard:
https://github.com/bemanproject/beman/blob/main/docs/BEMAN_STANDARD.md#cmakepassive_projects

Due to this setting, all the CI jobs were running with C++26 set, making the C++20 jobs spuriously pass. This commit removes them.

[coveralls]

coverage: 92.578% (+0.4%) from 92.179%
when pulling 2c8d96d on enolan_cppversionfix1
into 196e80d on main.

[dietmarkuehl]

I see you also disabled C++20. I thought the code would build with C++20. I may need to have a look at what breaks with C++20.

As an aside, I noticed the generic presets (debug and release) don't work with the setup from infra. That's a bit sad (I think I saw that Claus did have a PR for that but I haven't looked, yet).

[ednolan]

This was the error I got when I tried building with Clang 20 and C++20:

[374/396] /usr/local/bin/clang++ -DCMAKE_INTDIR=\"Release\" -I/home/eddie/sync/cpp/bemanproject/execution/include -stdlib=libc++ -O3  -O3 -DNDEBUG -std=gnu++20 -MD -MT examples/CMakeFiles/beman.execution.examples.intro-5-consumer.dir/Release/intro-5-consumer.cpp.o -MF examples/CMakeFiles/beman.execution.examples.intro-5-consumer.dir/Release/intro-5-consumer.cpp.o.d -o examples/CMakeFiles/beman.execution.examples.intro-
5-consumer.dir/Release/intro-5-consumer.cpp.o -c /home/eddie/sync/cpp/bemanproject/execution/examples/intro-5-consumer.cpp
FAILED: [code=1] examples/CMakeFiles/beman.execution.examples.intro-5-consumer.dir/Release/intro-5-consumer.cpp.o
/usr/local/bin/clang++ -DCMAKE_INTDIR=\"Release\" -I/home/eddie/sync/cpp/bemanproject/execution/include -stdlib=libc++ -O3  -O3 -DNDEBUG -std=gnu++20 -MD -MT examples/CMakeFiles/beman.execution.examples.intro-5-consumer.dir/Release/intro-5-consumer.cpp.o -MF examples/CMakeFiles/beman.execution.examples.intro-5-consumer.dir/Release/intro-5-consumer.cpp.o.d -o examples/CMakeFiles/beman.execution.examples.intro-5-consumer
.dir/Release/intro-5-consumer.cpp.o -c /home/eddie/sync/cpp/bemanproject/execution/examples/intro-5-consumer.cpp
/home/eddie/sync/cpp/bemanproject/execution/examples/intro-5-consumer.cpp:24:29: error: no template named 'expected' in namespace 'std'
   24 |         auto set_value(std::expected<Value, Error>&& exp) noexcept -> void {
      |                        ~~~~~^
/home/eddie/sync/cpp/bemanproject/execution/examples/intro-5-consumer.cpp:91:33: error: no member named 'expected' in namespace 'std'
   91 |     ex::sync_wait(ex::just(std::expected<success, failure>(success::one)) | expected_to_channel() |
      |                            ~~~~~^
/home/eddie/sync/cpp/bemanproject/execution/examples/intro-5-consumer.cpp:91:42: error: 'success' does not refer to a value
   91 |     ex::sync_wait(ex::just(std::expected<success, failure>(success::one)) | expected_to_channel() |
      |                                          ^
/home/eddie/sync/cpp/bemanproject/execution/examples/intro-5-consumer.cpp:15:12: note: declared here
   15 | enum class success : std::uint8_t { one };
      |            ^
/home/eddie/sync/cpp/bemanproject/execution/examples/intro-5-consumer.cpp:91:51: error: 'failure' does not refer to a value
   91 |     ex::sync_wait(ex::just(std::expected<success, failure>(success::one)) | expected_to_channel() |
      |                                                   ^
/home/eddie/sync/cpp/bemanproject/execution/examples/intro-5-consumer.cpp:16:12: note: declared here
   16 | enum class failure : std::uint8_t { fail_one };
      |            ^
4 errors generated.

[ednolan]

As an aside, I noticed the generic presets (debug and release) don't work with the setup from infra. That's a bit sad (I think I saw that Claus did have a PR for that but I haven't looked, yet).

I would like to upstream the fix for this into exemplar.

[dietmarkuehl]

As an aside, I noticed the generic presets (debug and release) don't work with the setup from infra. That's a bit sad (I think I saw that Claus did have a PR for that but I haven't looked, yet).

I would like to upstream the fix for this into exemplar.

I have accepted Claus’s change. It did restore something you removed (there was a conflict about it which I resolved in favor of Claus’s version).

[dietmarkuehl]

This was the error I got when I tried building with Clang 20 and C++20:

[374/396] /usr/local/bin/clang++ -DCMAKE_INTDIR=\"Release\" -I/home/eddie/sync/cpp/bemanproject/execution/include -stdlib=libc++ -O3  -O3 -DNDEBUG -std=gnu++20 -MD -MT examples/CMakeFiles/beman.execution.examples.intro-5-consumer.dir/Release/intro-5-consumer.cpp.o -MF examples/CMakeFiles/beman.execution.examples.intro-5-consumer.dir/Release/intro-5-consumer.cpp.o.d -o examples/CMakeFiles/beman.execution.examples.intro-
5-consumer.dir/Release/intro-5-consumer.cpp.o -c /home/eddie/sync/cpp/bemanproject/execution/examples/intro-5-consumer.cpp
FAILED: [code=1] examples/CMakeFiles/beman.execution.examples.intro-5-consumer.dir/Release/intro-5-consumer.cpp.o
/usr/local/bin/clang++ -DCMAKE_INTDIR=\"Release\" -I/home/eddie/sync/cpp/bemanproject/execution/include -stdlib=libc++ -O3  -O3 -DNDEBUG -std=gnu++20 -MD -MT examples/CMakeFiles/beman.execution.examples.intro-5-consumer.dir/Release/intro-5-consumer.cpp.o -MF examples/CMakeFiles/beman.execution.examples.intro-5-consumer.dir/Release/intro-5-consumer.cpp.o.d -o examples/CMakeFiles/beman.execution.examples.intro-5-consumer
.dir/Release/intro-5-consumer.cpp.o -c /home/eddie/sync/cpp/bemanproject/execution/examples/intro-5-consumer.cpp
/home/eddie/sync/cpp/bemanproject/execution/examples/intro-5-consumer.cpp:24:29: error: no template named 'expected' in namespace 'std'
   24 |         auto set_value(std::expected<Value, Error>&& exp) noexcept -> void {
      |                        ~~~~~^
/home/eddie/sync/cpp/bemanproject/execution/examples/intro-5-consumer.cpp:91:33: error: no member named 'expected' in namespace 'std'
   91 |     ex::sync_wait(ex::just(std::expected<success, failure>(success::one)) | expected_to_channel() |
      |                            ~~~~~^
/home/eddie/sync/cpp/bemanproject/execution/examples/intro-5-consumer.cpp:91:42: error: 'success' does not refer to a value
   91 |     ex::sync_wait(ex::just(std::expected<success, failure>(success::one)) | expected_to_channel() |
      |                                          ^
/home/eddie/sync/cpp/bemanproject/execution/examples/intro-5-consumer.cpp:15:12: note: declared here
   15 | enum class success : std::uint8_t { one };
      |            ^
/home/eddie/sync/cpp/bemanproject/execution/examples/intro-5-consumer.cpp:91:51: error: 'failure' does not refer to a value
   91 |     ex::sync_wait(ex::just(std::expected<success, failure>(success::one)) | expected_to_channel() |
      |                                                   ^
/home/eddie/sync/cpp/bemanproject/execution/examples/intro-5-consumer.cpp:16:12: note: declared here
   16 | enum class failure : std::uint8_t { fail_one };
      |            ^
4 errors generated.

OK, that makes sense: I guess I should disable this example (and possibly others) when building with a C++ version which doesn’t have the corresponding components.