FTBFS against g++ 11

I was able to reproduce it in sbuild locally.

But reproducing it from upstream git did not work well.
Neither with libgmock-dev from the package

   $ ./configure --enable-testing
   $ make
   $ apt install libgmock-dev
   # that is version 1.11.0-3
   $ make unit-test

Nor using upstreams get-mock as outlined in their readme

   $ apt remove libgmock-dev
   $ ./get-gmock.sh
   # that fetches head which is at 97a46757 (1.11 plus a few fixes)
   $ make clean
   $ make
   $ make unit-test

Both tests fail, but they do so at different places than the package build
Fails, but slightly different (also build errors)
./persistent-data/data-structures/btree.tcc:698:35: error: no match for ‘operator!=’ (operand types are ‘const value_type’ {aka ‘const {anonymous}::thing’} and ‘{anonymous}::thing_traits::value_type’ {aka ‘{anonymous}::thing’})
  698 | if (value != old_value) {

Furthermore whatever the problem is with upstream, this one does not go away when installing and forcing gcc-10

Therefore - as-is - I can't report that upstream in a useful way.
Our issue is somewhat special to Debian/Ubuntu builds.

Looking at our delta to upstream ...

There is some test delta, but for boost and I'd not see an immediate conenction to our FTBFS fails we see.

But what I was able to confirm was that setting it back to use gcc-10 for now works.
The following gets the build in Jammy working.

diff --git a/debian/control b/debian/control
index 5964039..bd1452a 100644
--- a/debian/control
+++ b/debian/control
@@ -12,6 +12,8 @@ Build-Depends:
  libexpat1-dev,
  libgtest-dev,
  google-mock,
+ gcc-10,
+ g++-10,
 Standards-Version: 3.9.5
 Vcs-Git: https://salsa.debian.org/lvm-team/thin-provisioning-tools.git
 Vcs-Browser: https://salsa.debian.org/lvm-team/thin-provisioning-tools
diff --git a/debian/rules b/debian/rules
index f9fa1cc..6c2401f 100755
--- a/debian/rules
+++ b/debian/rules
@@ -5,6 +5,8 @@
 #export DH_VERBOSE=1

 export DEB_BUILD_MAINT_OPTIONS = optimize=-lto
+export CC=gcc-10
+export CXX=g++-10

 include /usr/share/dpkg/default.mk

Maybe the real test fixup needs more domain knowledge or time, we can wait for the Debian bug to be resolved by the maintainer who wrote the tests (as I said above, upstream git behaves different).

Until then the change above will resolve the issue for us and get this out of excuses.

MR approved and uploaded to Jammy.

This bug was fixed in the package thin-provisioning-tools - 0.9.0-1ubuntu3

---------------
thin-provisioning-tools (0.9.0-1ubuntu3) jammy; urgency=medium

  * d/control, d/rules: force gcc-10 to avoid a gcc-11 FTBFS
    for now (LP: #1950028)

 -- Christian Ehrhardt <email address hidden> Thu, 16 Dec 2021 11:30:28 +0100