build: add reusable CMake library target for downstream projects

[m-mcgowan]

Adds a reusable CMake library target, so that downstream targets don't have to deal with note-c internals, and can opt-in to build the tests.

This builds on PR #225, since those fixes are needed to get a clean build on macOS.

Summary

• Adds a note_c_lib static library target that downstream projects (e.g. note-posix) can consume via add_subdirectory and target_link_libraries, without pulling in the unit test harness, 32-bit cross-compile flags, or FFF interposition settings, which are specific to the tests.
• Defaults NOTE_C_BUILD_TESTS to ON only when note-c is the top-level project (using PROJECT_IS_TOP_LEVEL), so subdirectory consumers skip tests automatically.
• Bumps cmake_minimum_required from 3.20 to 3.21 for PROJECT_IS_TOP_LEVEL support.
• Includes an integration test (test/integration/) that exercises the add_subdirectory workflow end-to-end.

Usage

  add_subdirectory(note-c)
  target_link_libraries(my_app PRIVATE note_c_lib)

The note_c_lib target carries the public include path, platform compile definitions (HAVE_STRLCPY, etc.), and all build options (NOTE_C_LOW_MEM, NOTE_C_SINGLE_PRECISION, etc.) — but none of the test-specific settings.

Test plan

• Existing unit tests pass (Linux CI unchanged)
• Integration test builds and passes (test/integration/)
• Verified with https://github.com/zakoverflow/note-posix — pristine clone builds and passes all 13 tests on macOS using note_c_lib

[zfields]

Pretty cool! 🌟

I'm tending a dumpster fire at the moment 🔥, but I am excited to check this one out! 😎

Cheers!

[m-mcgowan]

Pretty cool! 🌟

I'm tending a dumpster fire at the moment 🔥, but I am excited to check this one out! 😎

Cheers!

Any updates?

[zakoverflow]

Suggested cleanup around NOTE_C_NO_LIBC: I think this option should stay scoped to the shared note_c test/audit target, since its mechanism is link-time undefined-symbol auditing for scripts/check_libc_dependencies.sh.

The note_c_lib target is static, so its PRIVATE link options do not perform that audit at archive creation time, and they also should not propagate into downstream applications. Removing the block from note_c_lib makes that intent clearer while preserving the current CI check on note_c.

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2eaa1a7..xxxxxxx 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -21,11 +21,18 @@ option(NOTE_C_LOW_MEM "Build the library tailored for low memory usage." OFF)
 option(NOTE_C_MEM_CHECK "Run tests with Valgrind." OFF)
 option(NOTE_NODEBUG "Build the library without debug information." OFF)
-option(NOTE_C_NO_LIBC "Build the library without linking against libc, generating errors for any undefined symbols." OFF)
+option(NOTE_C_NO_LIBC "Audit libc dependencies by linking the test shared library without libc." OFF)
 option(NOTE_C_SHOW_MALLOC "Build the library with flags required to log memory usage." OFF)
 option(NOTE_C_SINGLE_PRECISION "Use single precision for JSON floating point numbers." OFF)
 option(NOTE_C_HEARTBEAT_CALLBACK "Enable heartbeat callback support." OFF)
 
+if(NOTE_C_NO_LIBC AND NOT NOTE_C_BUILD_TESTS)
+    message(FATAL_ERROR
+        "NOTE_C_NO_LIBC is only meaningful for the note_c shared test/audit "
+        "target. Enable NOTE_C_BUILD_TESTS, or leave NOTE_C_NO_LIBC disabled "
+        "when consuming note_c_lib."
+    )
+endif()
+
 set(NOTE_C_SRC_DIR ${CMAKE_CURRENT_SOURCE_DIR})
@@ -97,15 +104,6 @@ else()
     )
 endif()
 
-if(NOTE_C_NO_LIBC)
-    target_link_options(
-        note_c_lib
-        PRIVATE
-            -nostdlib
-            -nodefaultlibs
-            LINKER:--no-undefined
-    )
-endif()
-
 if(NOTE_NODEBUG)
     target_compile_definitions(
         note_c_lib

The existing NOTE_C_NO_LIBC block on the shared note_c target should remain as-is, because that is the target the libc dependency scan actually validates.

[zakoverflow]

I would also wire the new test/integration project into CI so the add_subdirectory(note-c) + target_link_libraries(... note_c_lib) contract is actually exercised on every PR.

Suggested workflow addition:

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c845f41..xxxxxxx 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -198,6 +198,22 @@ jobs:
         run: |
           docker run --rm --volume $(pwd):/note-c/ --workdir /note-c/ --entrypoint ./scripts/run_cppcheck.sh ghcr.io/blues/note_c_ci:latest
 
+  run_integration_tests:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Configure add_subdirectory integration test
+        run: cmake -S test/integration -B build-integration
+
+      - name: Build add_subdirectory integration test
+        run: cmake --build build-integration --parallel $(nproc)
+
+      - name: Run add_subdirectory integration test
+        run: ctest --test-dir build-integration --output-on-failure
+
   run_macos_unit_tests:
     runs-on: macos-latest
 

This catches regressions in the exact downstream-consumer workflow introduced by this PR without pulling in the unit-test harness, 32-bit test flags, or FFF-specific settings.

[m-mcgowan]

Added the first commit to address your valid feedback, and a second commit as some cleanup to DRY up some definitions.

[zfields]

Thanks Mat! This was long overdue. 🙏

[m-mcgowan]

Thanks Mat! This was long overdue. 🙏

You're welcome. I have an open issue from March (#238) - keen to hear your thoughts on that perhaps with Ray's input? It's not specifically a note-c issue, more a notecard change, but note-c was the closest available place where I could raise the issue.