Convert to INTERFACE and verify headers

Convert to an interface library and use verify headers to test that headers are
self-contained and compile correctly by themselves. Test install at end of CI
and run both Asan and RWDI builds.

.github/workflows/ci.yml

@@ -82,13 +82,27 @@ jobs:
           echo ${{ matrix.config.cmake_args }}
           echo ${{ matrix.config.toolchain }}
           rm -rf .build
-          cmake ${{ matrix.config.cmake_args }} -DCMAKE_TOOLCHAIN_FILE="etc/${{ matrix.config.toolchain }}-toolchain.cmake" -B .build -S .
-      - name: CMake Build
+          cmake ${{ matrix.config.cmake_args }} -DCMAKE_INSTALL_PREFIX=.install -DCMAKE_TOOLCHAIN_FILE="etc/${{ matrix.config.toolchain }}-toolchain.cmake" -B .build -S .
+      - name: CMake ASAN Build
         run: |
           set -x
+          cmake --build .build --config Asan --target all_verify_interface_header_sets -- -k 0
           cmake --build .build --config Asan --target all -- -k 0
-      - name: CMake Test
+      - name: CMake ASAN Test
         run: |
           set -x
           [[ ! -z "${{ matrix.config.asan_options }}" ]]  && export ASAN_OPTIONS="${{ matrix.config.asan_options }}"
           ctest --build-config Asan --output-on-failure --test-dir .build
+      - name: CMake RWDI Build
+        run: |
+          set -x
+          cmake --build .build --config RelWithDebInfo --target all_verify_interface_header_sets -- -k 0
+          cmake --build .build --config RelWithDebInfo --target all -- -k 0
+      - name: CMake RWDI Test
+        run: |
+          set -x
+          ctest --build-config RelWithDebInfo --output-on-failure --test-dir .build
+      - name: Install
+        run: |
+          set -x
+          cmake -DCMAKE_INSTALL_PREFIX=.install --install .build --config RelWithDebInfo --component beman_optional26_development --verbose

CMakeLists.txt

@@ -31,8 +31,10 @@ if(OPTIONAL26_ENABLE_TESTING)
     FetchContent_MakeAvailable(googletest)
 endif()
 
+set(CMAKE_VERIFY_INTERFACE_HEADER_SETS ON)
+
 # Create the library target and named header set for beman_optional26
-add_library(beman_optional26 STATIC)
+add_library(beman_optional26 INTERFACE)
 target_sources(
     beman_optional26
     PUBLIC FILE_SET beman_optional26_headers TYPE HEADERS BASE_DIRS src include

Makefile

@@ -61,6 +61,7 @@ $(_build_path)/CMakeCache.txt: | $(_build_path) .gitmodules
 
 TARGET:=all
 compile: $(_build_path)/CMakeCache.txt ## Compile the project
+	cmake --build $(_build_path)  --config $(CONFIG) --target all_verify_interface_header_sets -- -k 0
 	cmake --build $(_build_path)  --config $(CONFIG) --target all -- -k 0
 
 install: $(_build_path)/CMakeCache.txt compile ## Install the project

src/beman/optional26/CMakeLists.txt

@@ -1,9 +1,6 @@
 # src/beman/optional26/CMakeLists.txt -*-cmake-*-
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-# Ensure that optional and iterator get compiled at least once
-target_sources(beman_optional26 PUBLIC optional.cpp detail/iterator.cpp)
-
 # The library is empty -- exclude it
 install(
     TARGETS beman_optional26

src/beman/optional26/tests/CMakeLists.txt

@@ -17,8 +17,6 @@ target_sources(
         optional_range_support.t.cpp
         optional_ref.t.cpp
         optional_ref_monadic.t.cpp
-        test_types.cpp
-        test_utilities.cpp
 )
 
 target_sources(