build(cmake): split libcuopt into cuopt_client / cuopt_mathopt / cuopt_routing component libs

[ramakrishnap-nv]

Splits libcuopt.so into three component shared libraries and ships libcuopt.so as a GNU ld script naming them.

Packaging is unchanged: still one libcuopt wheel and one libcuopt conda package.

Components

Component	Size	Contents	Depends on
cuopt_client	2.4 MB	host problem representation, parsers, wire protocol, LP/MIP and VRP gRPC clients	nothing — leaf, no CUDA
cuopt_routing	188 MB	VRP / routing engine	cuopt_client
cuopt_mathopt	258 MB	LP / MIP / QP / SOCP engine, utilities	cuopt_client

Stripped, built for the default architecture list (75–120). Neither engine depends on the other, which is what makes a per-solver package split possible later. cuopt_client pulls in no CUDA, rmm or raft, so it resolves standalone.

-lcuopt keeps working; new code should prefer linking the component it uses.

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[ramakrishnap-nv]

/ok to test ec81ebc

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📝 Walkthrough

Walkthrough

The build now produces separate routing and mathematical-optimization libraries while preserving legacy libcuopt.so linking. Runtime loading, remote solving, symbol checks, packaging, examples, and gRPC coverage now use the component libraries.

Changes

Componentized build and linkage

Layer / File(s)	Summary
Component source aggregation cpp/src/**/CMakeLists.txt, cpp/CMakeLists.txt	CMake now propagates source lists and separates routing, mathematical-optimization, parser, and client sources.
Component libraries and compatibility linking cpp/CMakeLists.txt, cpp/cmake/libcuopt.so.in, cpp/include/cuopt/..., python/libcuopt/CMakeLists.txt	The build adds cuopt_routing and cuopt_mathopt, updates exported symbols and dependencies, installs component targets, and replaces the old shared cuopt implementation with a compatibility linker script.

Remote execution

Layer / File(s)	Summary
Remote solve dispatch cpp/cuopt_cli.cpp, cpp/src/mip_heuristics/solve.cu, cpp/src/pdlp/solve.cu, cpp/include/cuopt/mathematical_optimization/solve_remote.hpp	Remote LP and MIP requests validate CPU-backed inputs, dispatch through gRPC when available, and raise runtime errors when gRPC is unavailable.

Distribution and validation

Layer / File(s)	Summary
Loading, packaging, and validation python/libcuopt/libcuopt/load.py, ci/*, conda/recipes/libcuopt/recipe.yaml, docs/cuopt/**, cpp/tests/linear_programming/grpc/grpc_integration_test.cpp	Component libraries are loaded, packaged, linked by examples, checked for symbols, included in package contents, and covered by a VRP integration test.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Refactor

Merge Risk: 🟠 High · up to 0218b

Direct compatibility linking and non-gRPC builds can fail, while an optional routing failure can prevent Python from loading mathopt. These issues should be fixed before merge.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 12 functions across 16 files. (14 skipped…	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly and concisely describes the primary change: splitting libcuopt into cuopt_client, cuopt_mathopt, and cuopt_routing component libraries.
Description check	✅ Passed	The description directly explains the component-library split, compatibility linker script, packaging, dependencies, and limitations. It is fully related to the changeset.

Full details: Docstring Coverage

Explanation

Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 12 functions across 16 files. (14 skipped: 14 unsupported.)

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Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

cpp/CMakeLists.txt (1)

902-918: 🗄️ Data Integrity & Integration | 🟠 Major | ⚡ Quick win

Exported component names should match the documented API

cuopt::base / cuopt::lp are build-tree aliases only. The install/export set will expose the real targets (cuopt::cuopt_base, cuopt::cuopt_lp, etc.) unless those targets set EXPORT_NAME, so a consumer using find_package(cuopt) won’t be able to link against cuopt::base as documented.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@cpp/CMakeLists.txt` around lines 902 - 918, Update the component target
export configuration used by the rapids_export INSTALL and BUILD calls so
installed targets retain the documented names cuopt::base, cuopt::routing,
cuopt::lp, and cuopt::grpc. Set the appropriate EXPORT_NAME values on the
underlying cuopt_component targets, while preserving cuopt::cuopt as the
umbrella target and keeping build-tree aliases consistent.

🧹 Nitpick comments (2)

cpp/CMakeLists.txt (2)

549-556: 📐 Maintainability & Code Quality | 🔵 Trivial | 💤 Low value

Give the git hash lookup a fallback for non-git source trees.

Without RESULT_VARIABLE/ERROR_QUIET, tarball builds leak git's error to the configure log and bake an empty hash into build_info.hpp.

♻️ Proposed fallback

 execute_process(
         COMMAND git rev-parse --short HEAD
         WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
         OUTPUT_VARIABLE GIT_COMMIT_HASH
         OUTPUT_STRIP_TRAILING_WHITESPACE
+        RESULT_VARIABLE _git_hash_result
+        ERROR_QUIET
 )
+if(NOT _git_hash_result EQUAL 0 OR GIT_COMMIT_HASH STREQUAL "")
+    set(GIT_COMMIT_HASH "unknown")
+endif()

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@cpp/CMakeLists.txt` around lines 549 - 556, Update the git hash lookup in the
top-level CMake configuration to capture the execute_process result and suppress
stderr for source trees without Git metadata. When the lookup fails, assign a
stable non-empty fallback hash before the existing GIT_COMMIT_HASH message and
build_info.hpp generation; preserve the real short HEAD value for Git checkouts.

---

664-675: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚖️ Poor tradeoff

cuopt_objs duplicates the component include/definition setup.

The object library re-declares papilo/pslp/dejavu includes, CUDSS defines, and architecture defines that cuopt_configure_component (plus cuopt_lp) already establish. Since cuopt_objs backs cuopt_static for the test builds, drift here means tests compile under a different configuration than shipped libraries. Consider factoring the shared include/definition block into a helper both paths call.

Also applies to: 693-694, 720-724

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@cpp/CMakeLists.txt` around lines 664 - 675, Refactor the shared include
directories and compile definitions currently duplicated by cuopt_objs and the
cuopt_configure_component/cuopt_lp setup into a reusable CMake helper. Invoke
that helper for both cuopt_objs and the shipped-library path, including the
papilo/pslp/dejavu includes, CUDSS definitions, and architecture definitions,
while preserving target-specific settings such as POSITION_INDEPENDENT_CODE and
logging definitions.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Outside diff comments:
In `@cpp/CMakeLists.txt`:
- Around line 902-918: Update the component target export configuration used by
the rapids_export INSTALL and BUILD calls so installed targets retain the
documented names cuopt::base, cuopt::routing, cuopt::lp, and cuopt::grpc. Set
the appropriate EXPORT_NAME values on the underlying cuopt_component targets,
while preserving cuopt::cuopt as the umbrella target and keeping build-tree
aliases consistent.

---

Nitpick comments:
In `@cpp/CMakeLists.txt`:
- Around line 549-556: Update the git hash lookup in the top-level CMake
configuration to capture the execute_process result and suppress stderr for
source trees without Git metadata. When the lookup fails, assign a stable
non-empty fallback hash before the existing GIT_COMMIT_HASH message and
build_info.hpp generation; preserve the real short HEAD value for Git checkouts.
- Around line 664-675: Refactor the shared include directories and compile
definitions currently duplicated by cuopt_objs and the
cuopt_configure_component/cuopt_lp setup into a reusable CMake helper. Invoke
that helper for both cuopt_objs and the shipped-library path, including the
papilo/pslp/dejavu includes, CUDSS definitions, and architecture definitions,
while preserving target-specific settings such as POSITION_INDEPENDENT_CODE and
logging definitions.

---

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📒 Files selected for processing (13)

• conda/recipes/libcuopt/recipe.yaml
• cpp/CMakeLists.txt
• cpp/src/CMakeLists.txt
• cpp/src/barrier/CMakeLists.txt
• cpp/src/branch_and_bound/CMakeLists.txt
• cpp/src/cuts/CMakeLists.txt
• cpp/src/dual_simplex/CMakeLists.txt
• cpp/src/io/CMakeLists.txt
• cpp/src/linear_algebra/CMakeLists.txt
• cpp/src/math_optimization/CMakeLists.txt
• cpp/src/mip_heuristics/CMakeLists.txt
• cpp/src/pdlp/CMakeLists.txt
• cpp/src/routing/CMakeLists.txt

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/ok to test a54e62a

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/ok to test

[hlinsen]

Shouldn't we favor a breaking change here? Linking with -lcuopt keeps backward compatibility but I think we should ask users to link with -lcuopt_mathopt or -lcuopt_routing explicitely:

1. dlopen("libcuopt.so") does not work.
2. Packaging, Python loading, and symbol checks need special cases.
3. Users may reasonably assume a file named .so is an actual shared object

At least we should consider having a warning and deprecating -lcuopt in the next release.
I think we should consider it especially if users need to rebuild regardless.

"Anything previously linked against libcuopt.so needs a rebuild, since its DT_NEEDED now names a file that is not ELF."

[ramakrishnap-nv]

Agree, at the start I was thinking to keep libcuopt.so a simple layer to connect all, but things diverged, let me update it.

[ramakrishnap-nv]

Agreed on the direction, and I have taken your fallback in 2e9753a: keep -lcuopt working so this release does not break existing consumers, but stop making it the path of least resistance.

Your second point is measurably right — I count seven places carrying explicit "this is a linker script" handling: the conda recipe, load.py, python/libcuopt/CMakeLists.txt, the install rule, and three spots in cpp/CMakeLists.txt. The third is fair too; a .so that is a text script is surprising.

So both places a consumer would look now say to prefer the components. The generated script:

COMPATIBILITY SHIM. Prefer linking the components you actually use:

    -lcuopt_mathopt     LP / MIP / QP / SOCP
    -lcuopt_routing     VRP / TSP / PDP
    -lcuopt_client      host-side problem representation and gRPC client

and the installed CMake config's doc string names cuopt::mathopt / cuopt::routing / cuopt::client, with cuopt::cuopt described as backward compatibility that pulls both engines whether or not you use them. The script also now records the dlopen and naming consequences as reasons to move off -lcuopt rather than rely on it.

On breaking it outright in this release: I would rather not, because it breaks every existing C link line at once with no migration window, and it is severable from the split — the components and their boundaries stand on their own. What I have not done is add a build-time deprecation warning, only documentation. A DEPRECATION property on cuopt::cuopt would be the natural next step, but all nine Cython extension modules still link cuopt::cuopt today, so it would fire on our own build until #1635 relinks them to their actual component. That relinking is the first item on #1635, so the warning belongs with it.

Does documentation now plus the deprecation warning landing with #1635 work for you, or would you rather see the hard break in this PR?

[ramakrishnap-nv]

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Actionable comments posted: 6

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Inline comments:
In `@cpp/CMakeLists.txt`:
- Line 1068: Update CUOPT_LINKER_SCRIPT_INPUTS to append libcuopt_client.so
alongside the existing libcuopt_mathopt.so and conditional libcuopt_routing.so
inputs, so the generated libcuopt.so exposes client-owned symbols consistently
with the cuopt_client interface target.

In `@cpp/cuopt_cli.cpp`:
- Around line 218-221: Guard both solve_mip_remote and solve_lp_remote calls in
the CLI with CUOPT_ENABLE_GRPC; when gRPC is unavailable, log an error and
return -1 instead of referencing the remote templates, while preserving the
existing remote-call behavior for gRPC builds.

In `@cpp/src/pdlp/CMakeLists.txt`:
- Line 53: Update the source-list definitions in the CMake configuration so
solver_settings_accessors.cpp is removed from LP_CORE_FILES and retained only in
LP_CLIENT_FILES, while preserving the existing LP_SRC_FILES export to
cuopt_mathopt.

In `@docs/cuopt/source/cuopt-c/convex/examples/Makefile`:
- Line 49: Remove the -Wl,--allow-shlib-undefined linker flag from the LDFLAGS
definition, while preserving the cuOpt libraries, library search path, and
runtime rpath.

In `@docs/cuopt/source/cuopt-c/mip/examples/Makefile`:
- Line 25: Update the MIP example’s LDFLAGS to remove the
-Wl,--allow-shlib-undefined linker option while preserving the cuOpt libraries
and runtime-path settings.

In `@python/libcuopt/libcuopt/load.py`:
- Around line 62-67: Update _load_component so its OSError handling covers both
the preferred system-installation attempt and the wheel fallback. Preserve the
existing behavior of returning None for optional components and issuing the
warning/required-component failure path for required components, allowing
load_library to continue processing later components.

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📒 Files selected for processing (28)

• ci/build_wheel_cuopt.sh
• ci/check_symbols.sh
• ci/test_skills_assets.sh
• conda/recipes/libcuopt/recipe.yaml
• cpp/CMakeLists.txt
• cpp/cmake/libcuopt.so.in
• cpp/cuopt_cli.cpp
• cpp/include/cuopt/mathematical_optimization/solve_remote.hpp
• cpp/include/cuopt/utilities/timestamp_utils.hpp
• cpp/src/CMakeLists.txt
• cpp/src/cuts/CMakeLists.txt
• cpp/src/io/CMakeLists.txt
• cpp/src/io/mps_parser_internal.hpp
• cpp/src/math_optimization/CMakeLists.txt
• cpp/src/mip_heuristics/CMakeLists.txt
• cpp/src/mip_heuristics/solve.cu
• cpp/src/pdlp/CMakeLists.txt
• cpp/src/pdlp/solve.cu
• cpp/src/routing/CMakeLists.txt
• cpp/src/utilities/logger.hpp
• cpp/src/utilities/seed_generator.cuh
• cpp/src/utilities/version_info.hpp
• cpp/src/utilities/work_unit_scheduler.hpp
• cpp/tests/linear_programming/grpc/grpc_integration_test.cpp
• docs/cuopt/source/cuopt-c/convex/examples/Makefile
• docs/cuopt/source/cuopt-c/mip/examples/Makefile
• python/libcuopt/CMakeLists.txt
• python/libcuopt/libcuopt/load.py

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[hlinsen]

The new libraries do not appear to be tested independently. Can we update the C API tests to link only -lcuopt_mathopt and the routing tests to link only -lcuopt_routing? This would verify that each library provides all the required symbols and dependencies without relying on -lcuopt. We can keep a separate minimal test for backward compatibility.

• C API test links the aggregate cuopt target. It should exercise cuopt::mathopt.
• cuopttestutils also publicly pulls in aggregate cuopt. This could mask the C API test even after its direct dependency is changed.
• Routing example tests link aggregate cuopt. These should validate cuopt::routing.
• Routing gRPC tests link aggregate cuopt. Their exact client/routing dependencies should be explicit.
• The C asset CI links both -lcuopt and -lcuopt_mathopt. It should use only mathopt, with a separate legacy -lcuopt test.
• C documentation examples also link both libraries: convex and MIP.
• The future Cython migration is visible in routing and LP solver, both still using cuopt::cuopt.

[ramakrishnap-nv]

Good catch — that was a real gap, and fixing it found a second one. Done in 6f07ee6.

Each test now names the component it exercises:

target	links
C_API_TEST	cuopt_mathopt
routing example tests	cuopt_routing
GRPC_VRP_TEST_DRIVER	cuopt_routing + cuopt_client
routing gRPC mapper tests	cuopt_client

On your cuopttestutils point — it was worse than masking. It compiles routing/utilities/check_constraints.cu, so it is routing code, yet it linked the umbrella PUBLIC and C_API_TEST took it despite never using it. It now names cuopt_routing, is guarded on SKIP_ROUTING_BUILD, and C_API_TEST drops it entirely.

The two routing gRPC mapper tests I moved to cuopt_client alone rather than routing: the mappers are host-only. That link line now fails loudly if a mapper ever reaches into the engine.

Verified on the artifacts rather than on the build succeeding, since conda's LDFLAGS carries --allow-shlib-undefined and a clean build proves little here:

C_API_TEST                        NEEDED libcuopt_mathopt.so
GRPC_ROUTING_SETTINGS_MAPPER_TEST NEEDED libcuopt_client.so
GRPC_ROUTING_PROBLEM_MAPPER_TEST  NEEDED libcuopt_client.so
cvrp_daily_deliveries             NEEDED libcuopt_routing.so, libcuopt_client.so

No libcuopt.so on any of them, and all the relinked tests pass.

The C doc examples and ci/test_skills_assets.sh dropped the redundant -lcuopt from alongside -lcuopt_mathopt. The asset CI keeps one explicit -lcuopt build so the shim stays covered, per your "separate minimal test for backward compatibility".

Two things I did not fold in:

• The Cython modules still linking cuopt::cuopt — that is the first item on Split libcuopt wheel into separate routing/LP packages for PyPI publication #1635, since relinking them is what lets the deprecation warning fire without going off on our own build.
• Your earlier question on this thread about documentation now versus a build-time DEPRECATION warning with Split libcuopt wheel into separate routing/LP packages for PyPI publication #1635 is still open, and the answer drives the item above.

One caveat worth stating: I could not get a clean local link of the C doc examples, because this machine's conda env has since moved to rmm 26.12 while my build tree was compiled against 26.10, so libcuopt_mathopt.so has undefined rmm::_RMM_26_10:: references. The old -lcuopt -lcuopt_mathopt line fails identically, so it is environment skew rather than anything this change introduced — but the doc-example link is verified by CI here, not by me locally.

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[ramakrishnap-nv]

Reviewed the PR for more of this class of issue after the test relinking. Four found, one a real bug that would have shipped — bf680eb8.

1. cuopt_client exported logger state. ci/check_symbols.sh fails on the client while mathopt and routing pass:

ERROR: Logger state 'cuopt::default_logger()' is exported from libcuopt_client.so.
ERROR: Per-component loggers collapse into one.

cuopt_client is built from cuopt_client_objs, which never got the hidden visibility the other components get. Visibility is fixed when the objects are compiled, so putting it on the library built from them does nothing — the same OBJECT-library trap as the link-interface one earlier in this PR. Setting it on cuopt_client_objs drops those 4 symbols and 92 others, and every consumer still links, so the client's public surface was already annotated correctly.

Worth noting this is the same defect class as #1878, which I closed by marking one variable CUOPT_EXPORT. That fixed the symptom for t_log_callback while the library as a whole was still exporting with default visibility.

2. The client was never symbol-checked. The recipe checked mathopt and routing only, which is exactly why 1 survived. Added, so it cannot regress. Also corrected the stale component names in check_symbols.sh (base, grpc — both gone now).

3. cuopt_cli, solve_LP, solve_MIP linked the aggregate — the same thing you flagged for tests. cuopt_cli's real DT_NEEDED was already mathopt + client, with --as-needed dropping routing, so it never used the routing engine.

4. GRPC_VRP_TEST_DRIVER — correcting my previous comment: I said it links cuopt_routing + cuopt_client, but its DT_NEEDED was client only. It drives a server over gRPC and never calls the engine in process. Now declares cuopt_client alone.

Checked and found clean: no duplicate strong symbols across the three components (0 pairwise), the recipe ships all three, wheel RPATHs cover all five targets, and SKIP_ROUTING_BUILD / SKIP_GRPC_BUILD / both-together all configure.

Verification was done in a fresh conda env matching the pinned RAPIDS 26.10, since this machine had drifted to 26.12 nightlies — that skew was what blocked the doc-example link check in my previous comment. With a matching env all 9 C doc examples link with -lcuopt_mathopt alone, each with libcuopt_mathopt.so as their only cuOpt DT_NEEDED. Full C++ suite is 129/129.

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[hlinsen]

Thanks @ramakrishnap-nv!

Approved

[ramakrishnap-nv]

/merge