[Build] Compile and package on Ubuntu 26.04 (gcc 15)

[myungjoo]

Why

ppa:nnstreamer publishes nothing for Ubuntu 26.04 (resolute), and nnstreamer-edge is the first package that has to get there: nnstreamer-core depends on it. Two things stop the Launchpad recipe build of nnstreamer-edge on that series today.

1. The source stage never starts. Build-Depends names only gcc-9 | gcc-8 | gcc-7 | gcc-6 | gcc-5, none of which exist in Ubuntu 25.04 or later, so the recipe build parks in Dependency wait: gcc-9 (that is what happened on plucky, recipe build 3939544). Same fix as [Packaging] Add an unversioned gcc fallback to Build-Depends nnstreamer#4895: append the unversioned gcc, which the default compiler always provides.

2. gcc 15 rejects two lines under -Werror. Ubuntu 26.04 ships gcc 15, which compiles C as C23 by default; there glibc's strchr() and strstr() keep the constness of their argument, so storing the result in a char * is -Werror=discarded-qualifiers:

   nnstreamer-edge-util.c:131:13: error: initialization discards 'const' qualifier from pointer target type
   nnstreamer-edge-internal.c:2038:7: error: assignment discards 'const' qualifier from pointer target type
   

   Both pointers are only read (offset arithmetic and strcasecmp), so const char * is the correct type and compiles identically on every older compiler.

The unit tests need one more change to build there: the archive's googletest 1.17 refuses anything below C++17. Only the tests are C++, and nnstreamer itself already builds as C++17, so CMAKE_CXX_STANDARD goes from 14 to 17.

Regression coverage

The existing CMake workflow runs on the ubuntu-latest image, whose gcc does not default to C23 and whose gtest accepts C++14, so it could not catch either problem. This adds a second job in that workflow that builds and runs the tests inside a ubuntu:26.04 container. Without the source fixes that job fails exactly as the log above; with them it passes.

Verified

On an Ubuntu 26.04 container (gcc 15.2, gtest 1.17):

• cmake -DENABLE_TEST=ON + build + ctest: 2/2 tests pass.
• The same with -DMQTT_SUPPORT=ON, which is what debian/rules builds.
• dpkg-buildpackage -us -uc -b with the patched debian/control: nnstreamer-edge_0.2.8.0_amd64.deb and nnstreamer-edge-dev_0.2.8.0_amd64.deb build.

After merging

nnstreamer-edge-daily-2 on Launchpad needs Resolute added to its series and a build requested; adding a series alone does not trigger one. Part of nnstreamer/nnstreamer#4902.

🤖 Generated with Claude Code

[myungjoo]

[Automated review by a separate Claude agent, relayed to this PR]

No defects found. Findings, most important first:

• Suggestion (coverage): the new build-ubuntu-26-04 job configures with MQTT_SUPPORT off, but the Launchpad build this PR exists for runs debian/rules with -DMQTT_SUPPORT=ON (mosquitto). Adding libmosquitto-dev to the apt line and -DMQTT_SUPPORT=ON to the configure step would make CI compile nnstreamer-edge-mqtt-mosquitto.c under gcc 15 as well; the MQTT test is not registered with ADD_TEST, so ctest is unaffected. Not blocking: that file has no strchr/strstr call, and the PR body says MQTT=ON was verified locally.
• Nit: CMakeLists.txt:20 sets CMAKE_CXX_STANDARD 17 without CMAKE_CXX_STANDARD_REQUIRED ON, so a compiler without C++17 would silently decay instead of failing at configure. No current runner is that old, so optional.

What I checked:

• nnstreamer-edge-internal.c:2034-2052: s is used only in s - value, strcasecmp (s + 1, ...) and a %s log; nnstreamer-edge-util.c:131-136: p is used only in p - host_str and strtoll (p + 1, ...). All sinks take const char *, so const is correct and the behaviour is unchanged on older compilers.
• Grepped the whole head tree: these are the only two strchr/strstr/strrchr/strpbrk callers, so the MQTT, Tizen and custom-connection sources hide no third one.
• C++17 on existing runners: ubuntu-latest (gtest 1.14), pdebuild on jammy (gcc 11), and the GBS spec, which sets no -std=, all accept it. No docs still mention C++14.
• Workflow YAML: valid; the job already shows up as the check "Build and test on Ubuntu 26.04 (gcc 15)". Root container, so apt-get without sudo is right; pkg-config is installed for PKG_CHECK_MODULES(gtest); env.BUILD_TYPE is workflow-level and visible to the job.
• debian/control: gcc-5 (>=5.4) | gcc keeps the version relation bound to gcc-5 only, as before.
• Both commits carry a single Signed-off-by, matching signed-off-by.sh; the DCO check passes; subjects follow [Component] Summary.

[myungjoo]

[Relayed on behalf of the author by a Claude agent]

Both suggestions applied in the follow-up commit: the 26.04 job now installs libmosquitto-dev and configures with -DMQTT_SUPPORT=ON, matching debian/rules, and CMakeLists.txt sets CMAKE_CXX_STANDARD_REQUIRED ON. The MQTT configuration was also built on a 26.04 container before this PR was opened.