VS2017 + conan usage

[malachib]

Hey, firstly thank you for this amazing library!

Although this is primarily a conan issue, I'm hoping you have some expertise to help me out because the conan discussions go on for miles on the topic.

I am unable to do a conan install when using VS2017 due to:

ERROR: entt/3.5.2: Invalid configuration: entt requires a compiler that supports at least C++17

This is primarily because compiler.version=15 was the first release of VS2017 which had no C++17, but now it does. Conan has no notion of compiler.version=15.9, and conan's cppstd=17 isn't noticed because the compiler test fails first.

Do you have any suggestions for using VS2017 + conan + C++17? It seems a shame to go down the C++14 route (though I am doubly thankful, that you've provided that option)

[skypjack]

I've just enabled EnTT discussions here (finally, thanks GH!) and this questions is probably better suited for that.
Though, let's continue here anyway. Unfortunately, I'm not an expert of Conan, so I don't know how we can solve it but I'm interested in knowing this.
Maybe @Lawrencemm knows it? He uses Conan afaik and is by far more skilled than me.

[Lawrencemm]

Since this package doesn't need to be built, you can do a separate install: conan install entt/3.5.2 -s compiler.version=6 and it should work as a workaround until you find a better solution. (don't quote me on that command, I'm pretty sure you can install a single package but I can't remember the exact invocation)

[malachib]

The trouble we run in to is conan itself performs a compiler check during cmake scan. The conan VS/MSVC version managing is complicated to say the least. At any rate, at this point cmake halts because it:

"Detected a mismatch for the compiler version between your profile settings and CMake"

Which is actually technically true, since compiler.version=16 is VS2019

A workaround seems possible by using CONAN_DISABLE_CHECK_COMPILER but, kinda ew. Will try that and share my findings

UPDATE

Am met with error error C1007: unrecognized flag "-pdbrpc" in "p2" which is likely VS2017 attempting to use VS2019 link flags. Described more in detail here https://stackoverflow.com/questions/54664134/cannot-compile-unknown-flag-pdbrpc-in-p2
Also a ton of C4307 warnings about integral constant overflow. That's all kind of a rabbit hole.

Rather than going that way, I wonder - would be possible for entt packaging to be upgraded to permit compiler.version=15 if cppstd=17 is in effect?

[Lawrencemm]

Umm are you using the cmake generator for conan? If so I recommend switching to the cmake_find_package generator, it doesn't have these weird interactions and decouples the package manager from the build system.

Just remember to set the CMAKE_MODULE_PATH to the build directory when doing so, so that cmake finds the scripts conan generates.

[skypjack]

@malachib I'm more than willing to do what is needed in EnTT but you've to guide me because I've no clue of what is wrong and how to make it work. 🙂

[malachib]

Yeah, I am using the cmake generator. Giving cmake_find_package a try, it looks like a big improvement.

UPDATE

I've reworked things to use the suggested cmake_find_package generator. It's a universal improvement, but all the aforementioned compile/link issues persist.

It's a little mysterious to me what piece of conan is actually generating that requires a compiler message in the first place. This link: https://stackoverflow.com/questions/64694269/getting-uwebsockets-for-visual-2017-via-conan is seemingly exactly our issue, but the big difference is their conanfile.py actually includes that error message - where we quite reasonably do not. I figure if I can find the chunk of code generating it, maybe can work backwards to accommodate its wishes. Closest I can find is:

https://github.com/conan-io/conan-center-index/blob/master/recipes/cpp-taskflow/all/conanfile.py but frankly that seems like a random shot in the dark.

I'm confused 😕

[skypjack]

What about contacting someone from Conan for this? Maybe they can provide a solution that we don't see.

[Lawrencemm]

@malachib I'd be happy to help further, maybe move this to the discussions area or the discord so we can keep the EnTT issues clean 😅

[jgsogo]

Hi!

The error comes from this condition in the conanfile.py (https://github.com/conan-io/conan-center-index/blob/master/recipes/entt/3.x.x/conanfile.py#L42)... assuming you are using the reference from ConanCenter. The recipe is wrong, you should be able to provide a profile like:

[settings]
...
compiler.version=15
compiler.cppstd=17

and it should work, Conan would inject the flag to use C++17 and the library will compile... but given the checks in the recipe, that configuration will fail too.

Let me submit a PR to ConanCenter to fix the issue.

[malachib]

Creating #612 as suggested 😄

[skypjack]

We can directly convert the issue in a discussion. I think it's better, so as to maintain the history.
Don't get offense, but I'm deleting #612 and moving on this one. 🙂

Here is the last comment by @malachib from the discussion he created:

I didn't anticipate that in conan's own github repo there would be some entt configurations! Fascinating
@skypjack @Lawrencemm I appreciate how much you two dug into this, knowing full well it was a conan-sided thing all along

[malachib]

Relinking conan-io/conan-center-index#3840 for fun and profit
Really digging cmake_find_packages !

[Lawrencemm]

Ah that's good to hear @malachib. @jgsogo thank you very much for helping us out

[skypjack]

So, the conan-sided issue is solved as far as I can tell and EnTT works correctly also when using conan with VS2017.
Can you confirm this @malachib (because I didn't try it actually 🙂)? Thanks!

[malachib]

Been so slammed!!
Yes it works
Thank you!