build: make pkg-config optional for the system libunwind/breakpad options

CHANGELOG.md

@@ -21,6 +21,7 @@
 - Improve log and metric delivery when telemetry is captured faster than envelopes can be serialized by offloading serialization to an internal thread pool. ([#1946](https://github.com/getsentry/sentry-native/pull/1946))
 - Wine: fix OS version detection and cross-compiling Windows builds from Linux. ([#2001](https://github.com/getsentry/sentry-native/pull/2001))
 - Destroy condition variables as approriate when no longer needed. ([#2004](https://github.com/getsentry/sentry-native/pull/2004))
+- CMake: `pkg-config` is no longer a hard build requirement. `SENTRY_LIBUNWIND_SYSTEM` and `SENTRY_BREAKPAD_SYSTEM` still prefer the `pkg-config` metadata of the system package, but now fall back to `find_library()`/`find_path()` when the tool or the `.pc` file is missing. The same applies to the exported CMake config, which no longer requires consumers of a static build to have `pkg-config` installed.
 - Crashpad/Windows: preserve module CodeView UUIDs for minimal PDB70 records with empty PDB filenames. ([#2003](https://github.com/getsentry/sentry-native/pull/2003))
 
 ## 0.16.3

CMakeLists.txt

@@ -640,6 +640,7 @@ if(WIN32)
 endif()
 
 include(cmake/utils.cmake)
+include(cmake/sentry-find-system-library.cmake)
 if (WIN32 AND SENTRY_BUILD_SHARED_LIBS)
 	sentry_add_version_resource(sentry "Client Library")
 endif()
@@ -705,12 +706,11 @@ endif()
 if(SENTRY_WITH_LIBUNWIND)
 	if(LINUX)
 		if(SENTRY_LIBUNWIND_SYSTEM)
-			find_package(PkgConfig REQUIRED)
-			pkg_check_modules(LIBUNWIND REQUIRED IMPORTED_TARGET libunwind)
+			sentry_find_libunwind()
 			if(SENTRY_BUILD_SHARED_LIBS)
-				target_link_libraries(sentry PRIVATE PkgConfig::LIBUNWIND)
+				target_link_libraries(sentry PRIVATE sentry::libunwind)
 			else()
-				target_link_libraries(sentry PUBLIC PkgConfig::LIBUNWIND)
+				target_link_libraries(sentry PUBLIC sentry::libunwind)
 			endif()
 		else()
 			# Use vendored libunwind
@@ -802,13 +802,12 @@ elseif(SENTRY_BACKEND_BREAKPAD)
 	option(SENTRY_BREAKPAD_SYSTEM "Use system breakpad" OFF)
 	if(SENTRY_BREAKPAD_SYSTEM)
 		target_compile_definitions(sentry PRIVATE SENTRY_BREAKPAD_SYSTEM)
-		# system breakpad is using pkg-config, see `external/breakpad/breakpad-client.pc.in`
-		find_package(PkgConfig REQUIRED)
-		pkg_check_modules(BREAKPAD REQUIRED IMPORTED_TARGET breakpad-client)
+		# system breakpad ships pkg-config metadata, see `external/breakpad/breakpad-client.pc.in`
+		sentry_find_breakpad_client()
 		if(SENTRY_BUILD_SHARED_LIBS)
-			target_link_libraries(sentry PRIVATE PkgConfig::BREAKPAD)
+			target_link_libraries(sentry PRIVATE sentry::breakpad-client)
 		else()
-			target_link_libraries(sentry PUBLIC PkgConfig::BREAKPAD)
+			target_link_libraries(sentry PUBLIC sentry::breakpad-client)
 		endif()
 	else()
 		add_subdirectory(external)
@@ -934,8 +933,8 @@ elseif(SENTRY_BACKEND_NATIVE)
 
 	if(SENTRY_WITH_LIBUNWIND AND LINUX)
 		if(SENTRY_LIBUNWIND_SYSTEM)
-			pkg_check_modules(LIBUNWIND_PTRACE REQUIRED IMPORTED_TARGET libunwind-ptrace)
-			target_link_libraries(sentry-crash PRIVATE PkgConfig::LIBUNWIND PkgConfig::LIBUNWIND_PTRACE)
+			sentry_find_libunwind_ptrace()
+			target_link_libraries(sentry-crash PRIVATE sentry::libunwind sentry::libunwind-ptrace)
 		else()
 			# Use unwind_remote for the daemon (includes ptrace accessors
 			# for remote DWARF unwinding of the crashed process)
@@ -1018,6 +1017,8 @@ sentry_install(
 	FILES
 		"${PROJECT_BINARY_DIR}/sentry-config.cmake"
 		"${PROJECT_BINARY_DIR}/sentry-config-version.cmake"
+		# `sentry-config.cmake` recreates the system-library targets for consumers of a static build
+		"${SENTRY_SOURCE_DIR}/cmake/sentry-find-system-library.cmake"
 	DESTINATION "${CMAKE_INSTALL_CMAKEDIR}")
 if(WIN32 AND MSVC AND SENTRY_BUILD_SHARED_LIBS)
 	sentry_install(FILES $<TARGET_PDB_FILE:sentry>

README.md

@@ -266,15 +266,20 @@ using `cmake -D BUILD_SHARED_LIBS=OFF ..`.
   This instructs the build system to use system-installed breakpad libraries instead of the in-tree version.
 
 - `SENTRY_LIBUNWIND_SYSTEM` (Default: `OFF`, only for Linux):
-  This instructs the build system to use a system-installed `libunwind` (found via `pkg-config`) instead of the
-  vendored copy in `vendor/libunwind`.
+  This instructs the build system to use a system-installed `libunwind` instead of the vendored copy in
+  `vendor/libunwind`.
 
   In contrast to the vendored `libunwind` which is always built as a static archive and either linked into the
   resulting shared library or colocated with the other static artifacts, with `SENTRY_LIBUNWIND_SYSTEM=ON`, the library
   type (shared or static) is determined by the host distribution's package. The `SENTRY_BUILD_SHARED_LIBS` option only
   controls how the dependency is exposed to consuming CMake projects, not the library type of the system `libunwind`
   itself. Ensure matching build and target environments when using system packages.
 
+  Both `SENTRY_BREAKPAD_SYSTEM` and `SENTRY_LIBUNWIND_SYSTEM` read the `pkg-config` metadata of the system package
+  when `pkg-config`/`pkgconf` is installed, and fall back to CMake's own `find_library()`/`find_path()` lookup when it
+  is not, so `pkg-config` is a convenience rather than a build requirement for either option. The only remaining
+  build-time user of `pkg-config` is the vendored `crashpad`, and only on Linux with `CRASHPAD_ENABLE_STACKTRACE=ON`.
+
 - `SENTRY_TRANSPORT_COMPRESSION` (Default: `OFF`):
   Adds Gzip transport compression. Requires `zlib`.
 

cmake/sentry-find-system-library.cmake

@@ -0,0 +1,104 @@
+# Locates a system library the way CMake's own find modules do: `pkg-config` supplies search hints
+# when it happens to be installed, and `find_library()`/`find_path()` do the actual lookup either way.
+# See `FindLibinput`, `FindFontconfig` and the other bundled modules that follow the same shape.
+#
+# The only places sentry-native consults `pkg-config` are the optional `SENTRY_LIBUNWIND_SYSTEM` and
+# `SENTRY_BREAKPAD_SYSTEM` code paths, and only on Linux. Requesting it with
+# `find_package(PkgConfig REQUIRED)` nevertheless turned the tool into a hard build requirement for
+# anyone packaging sentry-native, which is why package managers end up declaring it on every platform,
+# including those where it is never invoked.
+#
+# Defines the imported target `TARGET` on success, and fails through
+# `find_package_handle_standard_args()` with the usual "could not find" diagnostic otherwise.
+#
+#	sentry_find_system_library(<Name>
+#		TARGET <target>
+#		PKG_CONFIG_MODULE <module>
+#		LIBRARY_NAMES <name>...
+#		[HEADER_NAMES <header>...]
+#		[HEADER_PATH_SUFFIXES <suffix>...])
+function(sentry_find_system_library NAME)
+	cmake_parse_arguments(SFSL "" "TARGET;PKG_CONFIG_MODULE"
+		"LIBRARY_NAMES;HEADER_NAMES;HEADER_PATH_SUFFIXES" ${ARGN})
+
+	if(TARGET "${SFSL_TARGET}")
+		return()
+	endif()
+
+	# Hints only. A missing tool or a missing `.pc` file just leaves the hints empty. The guard is
+	# needed because `pkg_check_modules()` is defined by `FindPkgConfig` itself, so it does not exist
+	# when that module was never loaded.
+	find_package(PkgConfig QUIET)
+	if(PKG_CONFIG_FOUND)
+		pkg_check_modules(PC_${NAME} QUIET "${SFSL_PKG_CONFIG_MODULE}")
+	endif()
+
+	set(libraries "")
+	set(required_vars "")
+	foreach(library_name IN LISTS SFSL_LIBRARY_NAMES)
+		string(MAKE_C_IDENTIFIER "${NAME}_${library_name}_LIBRARY" cache_var)
+		find_library("${cache_var}" NAMES "${library_name}" HINTS ${PC_${NAME}_LIBRARY_DIRS})
+		mark_as_advanced("${cache_var}")
+		list(APPEND libraries "${${cache_var}}")
+		list(APPEND required_vars "${cache_var}")
+	endforeach()
+
+	if(SFSL_HEADER_NAMES)
+		find_path(${NAME}_INCLUDE_DIR
+			NAMES ${SFSL_HEADER_NAMES}
+			HINTS ${PC_${NAME}_INCLUDE_DIRS}
+			PATH_SUFFIXES ${SFSL_HEADER_PATH_SUFFIXES})
+		mark_as_advanced(${NAME}_INCLUDE_DIR)
+		list(APPEND required_vars ${NAME}_INCLUDE_DIR)
+	endif()
+
+	# These lookups only run once the user has opted into a system library, so a miss is fatal.
+	# `find_package_handle_standard_args()` reads this to pick the failure mode and the message.
+	set(${NAME}_FIND_REQUIRED TRUE)
+	include(FindPackageHandleStandardArgs)
+	find_package_handle_standard_args(${NAME} REQUIRED_VARS ${required_vars})
+
+	add_library("${SFSL_TARGET}" INTERFACE IMPORTED)
+	set_target_properties("${SFSL_TARGET}" PROPERTIES INTERFACE_LINK_LIBRARIES "${libraries}")
+	if(${NAME}_INCLUDE_DIR)
+		set_target_properties("${SFSL_TARGET}" PROPERTIES
+			INTERFACE_INCLUDE_DIRECTORIES "${${NAME}_INCLUDE_DIR}")
+	endif()
+	if(PC_${NAME}_CFLAGS_OTHER)
+		set_target_properties("${SFSL_TARGET}" PROPERTIES
+			INTERFACE_COMPILE_OPTIONS "${PC_${NAME}_CFLAGS_OTHER}")
+	endif()
+endfunction()
+
+# The lookups below are shared between the build itself and the installed `sentry-config.cmake`, which
+# has to recreate the same imported targets for consumers of a static sentry-native. Keeping them here
+# means the two cannot drift.
+
+function(sentry_find_libunwind)
+	sentry_find_system_library(SentryLibunwind
+		TARGET sentry::libunwind
+		PKG_CONFIG_MODULE libunwind
+		LIBRARY_NAMES unwind
+		HEADER_NAMES libunwind.h)
+endfunction()
+
+function(sentry_find_libunwind_ptrace)
+	# `libunwind-ptrace.pc` declares `Requires: libunwind-generic libunwind`; the generic half has to
+	# be named here, and callers link `sentry::libunwind` alongside for the other.
+	sentry_find_system_library(SentryLibunwindPtrace
+		TARGET sentry::libunwind-ptrace
+		PKG_CONFIG_MODULE libunwind-ptrace
+		LIBRARY_NAMES unwind-ptrace unwind-generic
+		HEADER_NAMES libunwind-ptrace.h)
+endfunction()
+
+function(sentry_find_breakpad_client)
+	# `breakpad-client.pc` exposes the headers below `${includedir}/breakpad`, matching the
+	# `client/<os>/...` includes in `src/backends/sentry_backend_breakpad.cpp`.
+	sentry_find_system_library(SentryBreakpadClient
+		TARGET sentry::breakpad-client
+		PKG_CONFIG_MODULE breakpad-client
+		LIBRARY_NAMES breakpad_client
+		HEADER_NAMES google_breakpad/common/breakpad_types.h
+		HEADER_PATH_SUFFIXES breakpad)
+endfunction()

sentry-config.cmake.in

@@ -1,5 +1,6 @@
 @PACKAGE_INIT@
 include(CMakeFindDependencyMacro)
+include("${CMAKE_CURRENT_LIST_DIR}/sentry-find-system-library.cmake")
 
 set(SENTRY_BACKEND @SENTRY_BACKEND@)
 set(SENTRY_TRANSPORT @SENTRY_TRANSPORT@)
@@ -16,12 +17,10 @@ if(NOT SENTRY_BUILD_SHARED_LIBS)
 		find_dependency(ZLIB)
 	endif()
 	if(SENTRY_BACKEND STREQUAL "breakpad" AND SENTRY_BREAKPAD_SYSTEM)
-		find_dependency(PkgConfig)
-		pkg_check_modules(BREAKPAD REQUIRED IMPORTED_TARGET breakpad-client)
+		sentry_find_breakpad_client()
 	endif()
 	if(SENTRY_LIBUNWIND_SYSTEM)
-		find_dependency(PkgConfig)
-		pkg_check_modules(LIBUNWIND REQUIRED IMPORTED_TARGET libunwind)
+		sentry_find_libunwind()
 	endif()
 	if(SENTRY_TRANSPORT STREQUAL "curl" AND NOT SENTRY_LINK_CURL STREQUAL "OFF")
 		find_dependency(CURL)