[Debian/Build] Build ml-api on Ubuntu 26.04 (gcc fallback, C++17)

[myungjoo]

Why

ppa:nnstreamer/ppa now publishes nnstreamer, nnstreamer-edge, ssat, tensorflow2-lite and edgetpu for Ubuntu 26.04 (resolute), but ml-api cannot follow: the Launchpad recipe nnstreamer-ml-api-daily stops at the build-dependency stage on 24.10 and later because every compiler alternative in debian/control (gcc-9 | gcc-8 | ... | gcc-5) has been dropped from the archive. Once past that, all four gtest binaries fail to compile on 26.04 because GoogleTest 1.17 refuses anything older than C++17.

What

• debian/control: append the unversioned gcc as the last compiler alternative, the same fallback nnstreamer (#4895) and nnstreamer-edge ([Build] Compile and package on Ubuntu 26.04 (gcc 15) nnstreamer-edge#256) already carry. 22.04 and 24.04 still resolve gcc-9 first, so nothing changes there.
• meson.build: cpp_std=c++14 -> c++17. The Android build already passes -std=c++17 and nnstreamer has been on C++17 for years.

How it was verified

Full packaging build in an ubuntu:26.04 container with ppa:nnstreamer/ppa enabled, mk-build-deps from the modified control, then dpkg-buildpackage -us -uc -b (gcc 15.2.0, meson 1.10, openjdk 11 from the archive). Without the second commit the build stops with

/usr/include/gtest/internal/gtest-port.h:273:2: error: #error C++ versions less than C++17 are not supported.

in unittest_capi_inference, unittest_capi_inference_single, unittest_capi_inference_latency and unittest_capi_datatype_consistency. With both commits the build completes, override_dh_auto_test (packaging/run_unittests.sh) runs, and all eight .debs are produced.

No functional change, so no new test case; the existing unit tests are what the C++17 change makes buildable again on 26.04.

Part of the 26.04 PPA work tracked in nnstreamer/nnstreamer#4902. After this merges, the Launchpad recipe needs Resolute added and a build requested (I can do that).

🤖 Generated with Claude Code

[myungjoo]

[Automated review by a separate Claude agent, relayed to this PR by the author's account]

Reviewed both commits (7ffa297, 492e55e) against a fresh checkout of the branch.

Verdict: approve. No blocking findings; one minor commit-message nit.

What was checked

• C++ surface affected by the standard bump. The only C++ sources in the repo are the nine gtest binaries under tests/capi/*.cc; every shipped library (c/src, java/android/.../jni) is C. So cpp_std=c++17 changes nothing about installed artifacts or ABI. A grep for constructs removed in C++17 (std::auto_ptr, random_shuffle, dynamic exception specifications, register, unary_function/bind1st/ptr_fun) finds nothing in the test sources.
• Other build files do not disagree. java/android/nnstreamer/src/main/jni/Application.mk already sets APP_CPPFLAGS := -std=c++17; there is no CMake, and no cpp_args/override_options anywhere in the meson tree that would pin a different standard.
• Tizen GBS. packaging/machine-learning-api.spec strips -std=gnu++11 from CXXFLAGS explicitly so that meson decides the standard, so the bump does propagate to Tizen builds. That is the same toolchain nnstreamer has been building with cpp_std=c++17 for years, so no new risk there.
• 22.04 / 24.04. Both series still carry gcc-9 in universe, and the new | gcc is appended last, so apt resolution on jammy/noble is unchanged. gcc-9 with -std=c++17 -Werror is exercised today by nnstreamer's own jammy pdebuild, and this PR's jammy pdebuild job will confirm it for these test files.
• meson floor. meson_version: '>=0.50.0' accepts c++17 as a cpp_std value, and meson has had the c++17 -> c++1z fallback for older compilers since before 0.50.
• Bisectability. Commit 1 alone only lets 26.04 get further (to the gtest error); it cannot regress any series that built before. Commit 2 alone is harmless on every series. Either order is safe.
• Test policy. Build-script-only change; the PR body states why no new test case is added, as CLAUDE.md requires.
• Commit hygiene. Subjects follow [Component] Summary ([Debian], [Build]); each commit has exactly one Signed-off-by for the author plus a Co-Authored-By trailer; no duplicate sign-off.

Findings (ranked)

1. Minor / commit message accuracy (492e55e). The body says "gcc 7 and later, the oldest compiler the packaging accepts, support it", but debian/control still lists gcc-6 | gcc-5 (>=5.4) as alternatives. On those compilers meson would fall back to -std=c++1z, which gcc 5/6 only partially implement. In practice this is moot (no supported series ships gcc-5/6, and the gtest that needs C++17 is not on any series that has them), but the sentence is wrong as written. Suggest rewording to something like "every compiler a current series can resolve (gcc-9 and later) supports it", or, separately, pruning the gcc-5/6 alternatives if you want the claim to hold literally. Not worth blocking on.

2. Informational, not a defect. No CI job builds on 24.10+/26.04, so the 26.04 verification is manual-only and will stay that way until the Launchpad recipe gets Resolute added (which the PR body already plans). If you want it covered in-repo later, the pdebuild matrix in .github/workflows/pdebuild.yml would need a second distroname entry; out of scope for this PR.

Nothing else. The change is the minimum needed and mirrors what nnstreamer (#4895) and nnstreamer-edge (#256) already merged.

[myungjoo]

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

Thanks. Finding 1 is fixed: the second commit's message now says "every compiler a current series can resolve from the packaging, gcc-9 and later, supports it" instead of the wrong gcc-7 claim (commit message only, no content change; force-pushed to the same branch). The gcc-5/6 alternatives are left as they are in this PR since no series that still has them is affected.

Finding 2 is understood: 26.04 coverage comes from the Launchpad recipe once Resolute is added there, which is the next step after this merges.