Add project files.

cmake/Dependencies.cmake

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+# =============================================================================
+# Dependencies.cmake
+#
+# Three ways to bring in a third-party dependency, and one helper that ties
+# two of them together. All three keep the dependency's own warnings out of
+# your build (SYSTEM) and its sources out of compile_commands.json, so
+# clangd/clang-tidy stay focused on code this project owns.
+#
+#   add_vendor_header_only(NAME [INCLUDE_DIR <dir>])
+#       A buildless (header-only) drop checked into vendor/<NAME>/include
+#       (or vendor/<INCLUDE_DIR>). Wraps it as an INTERFACE target NAME.
+#
+#   add_vendor_subdirectory(SUBDIR)
+#       A vendored dependency that ships its own CMakeLists.txt, checked
+#       into vendor/<SUBDIR> (a plain source drop, git submodule, or git
+#       subtree). Whatever target names that CMakeLists.txt defines are
+#       what you DEPENDS on.
+#
+#   add_dependency(NAME <FetchContent_Declare args...>)
+#       CMake's native find_package + FetchContent integration: pass
+#       FIND_PACKAGE_ARGS ... to try an already-installed copy (an apt/
+#       vcpkg/conan package) first, and only download + build from source
+#       if nothing is found. Omit FIND_PACKAGE_ARGS to always fetch.
+#       https://cmake.org/cmake/help/latest/module/FetchContent.html#integrating-with-find-package
+#
+# All three are safe to call more than once for the same name (e.g. two
+# modules that both need the same dependency) -- later calls are no-ops.
+#
+# A module DEPENDS on whatever target the chosen path defines, exactly
+# like depending on another module -- add_lib_module/add_exe_module don't
+# need to know or care which of the three supplied it.
+#
+# IMPORTANT -- installing: a vendored/fetched dependency's own
+# CMakeLists.txt usually has its own install() rules, and there is no
+# reliable, version-independent way to suppress them from here (EXCLUDE_
+# FROM_ALL's effect on install() is explicitly documented as undefined,
+# and CMAKE_SKIP_INSTALL_RULES breaks `cmake --install` outright for
+# FetchContent -- both were tried and rejected). The actual fix lives in
+# CMakeLists.txt: our own install(TARGETS ...) calls are tagged
+# COMPONENT ${PROJECT_CODE_NAME}, and scripts/install.sh / install.bat always pass
+# --component so a third-party dependency's untagged install rules are
+# never pulled in. Installing with plain `cmake --install build` (no
+# --component) will also install whatever the dependency wanted to
+# install, typically under CMAKE_INSTALL_PREFIX (e.g. /usr/local) --
+# use the install script, or pass --component yourself.
+# =============================================================================
+
+include_guard(GLOBAL)
+
+# -----------------------------------------------------------------------
+# _exclude_from_compile_commands(DIR): drop every target defined under
+# DIR from compile_commands.json. Applied to vendored/fetched third-party
+# code so the exported compile database stays focused on code this
+# project actually owns.
+# -----------------------------------------------------------------------
+function(_exclude_from_compile_commands DIR)
+    if(NOT IS_DIRECTORY "${DIR}")
+        return()
+    endif()
+    get_property(_pmn_dir_targets DIRECTORY "${DIR}" PROPERTY BUILDSYSTEM_TARGETS)
+    foreach(_t ${_pmn_dir_targets})
+        set_target_properties(${_t} PROPERTIES EXPORT_COMPILE_COMMANDS OFF)
+    endforeach()
+endfunction()
+
+# -----------------------------------------------------------------------
+# add_vendor_header_only(NAME [INCLUDE_DIR <dir>])
+# -----------------------------------------------------------------------
+macro(add_vendor_header_only NAME)
+    cmake_parse_arguments(ARG "" "INCLUDE_DIR" "" ${ARGN})
+    if(NOT TARGET ${NAME})
+        add_library(${NAME} INTERFACE)
+        if(ARG_INCLUDE_DIR)
+            target_include_directories(${NAME} SYSTEM INTERFACE "${CMAKE_SOURCE_DIR}/vendor/${ARG_INCLUDE_DIR}")
+        else()
+            target_include_directories(${NAME} SYSTEM INTERFACE "${CMAKE_SOURCE_DIR}/vendor/${NAME}/include")
+        endif()
+    endif()
+endmacro()
+
+# -----------------------------------------------------------------------
+# add_vendor_subdirectory(SUBDIR)
+#
+# EXCLUDE_FROM_ALL means only targets actually depended on via
+# target_link_libraries get built. SYSTEM marks its headers so our
+# per-module warning flags (added only by add_lib_module/add_exe_module/
+# etc., never globally) don't fire when *our* code includes them.
+# -----------------------------------------------------------------------
+macro(add_vendor_subdirectory SUBDIR)
+    get_property(_pmn_vendor_added GLOBAL PROPERTY PMN_VENDOR_ADDED_${SUBDIR} SET)
+    if(NOT _pmn_vendor_added)
+        set_property(GLOBAL PROPERTY PMN_VENDOR_ADDED_${SUBDIR} TRUE)
+        add_subdirectory(
+            "${CMAKE_SOURCE_DIR}/vendor/${SUBDIR}"
+            "${CMAKE_BINARY_DIR}/vendor/${SUBDIR}"
+            EXCLUDE_FROM_ALL SYSTEM
+        )
+        _exclude_from_compile_commands("${CMAKE_SOURCE_DIR}/vendor/${SUBDIR}")
+    endif()
+endmacro()
+
+# -----------------------------------------------------------------------
+# add_dependency(NAME <FetchContent_Declare args...>)
+#
+# Example -- prefer an installed copy, fetch+build from source otherwise:
+#   add_dependency(fmt
+#       GIT_REPOSITORY https://github.com/fmtlib/fmt.git
+#       GIT_TAG        11.0.2
+#       FIND_PACKAGE_ARGS NAMES fmt
+#   )
+#   add_lib_module(mylib DEPENDS fmt::fmt)
+#
+# FetchContent_MakeAvailable() is documented idempotent per name, so
+# calling this more than once for the same NAME (from multiple modules)
+# is safe.
+# -----------------------------------------------------------------------
+macro(add_dependency NAME)
+    include(FetchContent)
+    FetchContent_Declare(${NAME} SYSTEM ${ARGN})
+    FetchContent_MakeAvailable(${NAME})
+    string(TOLOWER "${NAME}" _pmn_lc_name)
+    if(DEFINED ${_pmn_lc_name}_SOURCE_DIR)
+        _exclude_from_compile_commands("${${_pmn_lc_name}_SOURCE_DIR}")
+    endif()
+endmacro()