Compilation failure of cpr 1.12.0 on aarch64

[stephanlachnit]

Description

Since updating to 1.12.0, we got a build failure on aarch64 (arm):

../subprojects/cpr-1.12.0/include/cpr/session.h:55:7: error: type ‘struct Session’ violates the C++ One Definition Rule [-Werror=odr]
   55 | class Session : public std::enable_shared_from_this<Session> {
      |       ^
../subprojects/cpr-1.12.0/include/cpr/session.h:55:7: note: a different type is defined in another translation unit
   55 | class Session : public std::enable_shared_from_this<Session> {
      |       ^
../subprojects/cpr-1.12.0/include/cpr/session.h:255:13: note: the first difference of corresponding definitions is field ‘content_’
  255 |     Content content_{std::monostate{}};
      |             ^
../subprojects/cpr-1.12.0/include/cpr/session.h:255:13: note: a field of same name but different type is defined in another translation unit
  255 |     Content content_{std::monostate{}};
      |             ^
../subprojects/cpr-1.12.0/include/cpr/session.h:55:7: note: type ‘struct Content’ itself violates the C++ One Definition Rule
   55 | class Session : public std::enable_shared_from_this<Session> {
      |       ^

This does not happen on x86.

Example/How to Reproduce

1. Get access to an arm machine
2. git clone https://gitlab.desy.de/constellation/constellation.git && cd constellation
3. meson setup build -Dsatellite_mattermost=true
4. meson compile -C build

Possible Fix

No response

Where did you get it from?

Other (specify in "Additional Context/Your Environment")

Additional Context/Your Environment

• OS: Flatpak runtime (Linux) on aarch64
• Version: 1.12.0 (via Meson WrapDB)
• Build log: https://github.com/flathub-infra/vorarbeiter/actions/runs/18342359596/job/52240744126

[stephanlachnit]

This only seems to happen using static libraries, so this might as well be a bug in the Meson build files, investigating

[COM8]

@stephanlachnit thanks for reporting!
I can not reproduce this in my flatpak aarch64 build here: COM8/aps-ui#1

Not sure if you can the the CI log, but the flatpak itself builds with cpr1.12.0.

I will also try starting a static build to see what happens.

[stephanlachnit]

Logs for shared build which do not fail: https://github.com/flathub-infra/vorarbeiter/actions/runs/18372505318/job/52338896935

[stephanlachnit]

What I don't get is that all of the types that Content can be are just assembled from the standard library and do not sit behind any flags, so I don't get how this can cause a violation of ODR