Automate find_dependency generation for installed packages

Added logic to introspect INTERFACE_LINK_LIBRARIES and generate appropriate find_dependency() calls in installed CMake package config files. Updated documentation to explain dependency handling, added a helper function in cpp-library-install.cmake, and modified the config template to include generated dependencies. This ensures downstream users automatically find and link required dependencies.

Author: sean-parent

README.md

@@ -123,6 +123,46 @@ cmake --install build/default --prefix /opt/mylib
 
 For information about using installed packages with `find_package()`, see the [CPM.cmake documentation](https://github.com/cpm-cmake/CPM.cmake) about [controlling how dependencies are found](https://github.com/cpm-cmake/CPM.cmake#cpm_use_local_packages).
 
+#### Dependency Handling in Installed Packages
+
+cpp-library automatically generates correct `find_dependency()` calls in the installed CMake package configuration files by introspecting your target's `INTERFACE_LINK_LIBRARIES`. This ensures downstream users can find and link all required dependencies.
+
+**How it works:**
+
+When you link dependencies to your target using `target_link_libraries()`, cpp-library analyzes these links during installation and generates appropriate `find_dependency()` calls. For example:
+
+```cmake
+# In your library's CMakeLists.txt
+add_library(my-lib INTERFACE)
+
+# Link dependencies - these will be automatically handled during installation
+target_link_libraries(my-lib INTERFACE
+    stlab::copy-on-write    # Internal CPM dependency
+    stlab::enum-ops         # Internal CPM dependency
+    Threads::Threads        # System dependency
+)
+```
+
+When installed, the generated `my-libConfig.cmake` will include:
+
+```cmake
+include(CMakeFindDependencyMacro)
+
+# Find dependencies required by this package
+find_dependency(copy-on-write)
+find_dependency(enum-ops)
+find_dependency(Threads)
+
+include("${CMAKE_CURRENT_LIST_DIR}/my-libTargets.cmake")
+```
+
+**Supported dependency patterns:**
+
+- **CPM/Internal dependencies** (`namespace::target`): Automatically mapped to their package names (e.g., `stlab::copy-on-write` → `find_dependency(copy-on-write)`)
+- **Threading** (`Threads::Threads`): Generates `find_dependency(Threads)`
+- **Qt libraries** (`Qt5::Core`, `Qt6::Widgets`): Generates `find_dependency(Qt5 COMPONENTS Core)` with proper components
+- **Generic packages** (`PackageName::Target`): Generates `find_dependency(PackageName)`
+
 ### Updating cpp-library
 
 To update to the latest version of cpp-library in your project:

cmake/cpp-library-install.cmake

@@ -12,6 +12,58 @@
 include(GNUInstallDirs)
 include(CMakePackageConfigHelpers)
 
+# Generates find_dependency() calls for target's INTERFACE link libraries
+# - Precondition: TARGET_NAME specifies existing target with INTERFACE_LINK_LIBRARIES
+# - Postcondition: OUTPUT_VAR contains newline-separated find_dependency() calls for public dependencies
+# - Handles common patterns: namespace::target from CPM, Qt5/Qt6::Component, Threads::Threads, etc.
+function(_cpp_library_generate_dependencies OUTPUT_VAR TARGET_NAME NAMESPACE)
+    get_target_property(LINK_LIBS ${TARGET_NAME} INTERFACE_LINK_LIBRARIES)
+    
+    if(NOT LINK_LIBS)
+        set(${OUTPUT_VAR} "" PARENT_SCOPE)
+        return()
+    endif()
+    
+    set(DEPENDENCY_LIST "")
+    
+    foreach(LIB IN LISTS LINK_LIBS)
+        # Skip generator expressions (typically BUILD_INTERFACE dependencies)
+        if(LIB MATCHES "^\\$<")
+            continue()
+        endif()
+        
+        # Parse namespaced target: PackageName::Component
+        if(LIB MATCHES "^([^:]+)::(.+)$")
+            set(PKG_NAME "${CMAKE_MATCH_1}")
+            set(COMPONENT "${CMAKE_MATCH_2}")
+            
+            # Determine find_dependency() call based on package pattern
+            if(PKG_NAME STREQUAL NAMESPACE)
+                # Internal dependency: use component as package name (e.g., stlab::copy-on-write → copy-on-write)
+                list(APPEND DEPENDENCY_LIST "find_dependency(${COMPONENT})")
+            elseif(PKG_NAME STREQUAL "Threads")
+                list(APPEND DEPENDENCY_LIST "find_dependency(Threads)")
+            elseif(PKG_NAME MATCHES "^Qt[56]$")
+                # Qt with component (e.g., Qt5::Core → find_dependency(Qt5 COMPONENTS Core))
+                list(APPEND DEPENDENCY_LIST "find_dependency(${PKG_NAME} COMPONENTS ${COMPONENT})")
+            else()
+                # Generic package (e.g., libdispatch::libdispatch → libdispatch)
+                list(APPEND DEPENDENCY_LIST "find_dependency(${PKG_NAME})")
+            endif()
+        endif()
+    endforeach()
+    
+    # Remove duplicates and convert to newline-separated string
+    if(DEPENDENCY_LIST)
+        list(REMOVE_DUPLICATES DEPENDENCY_LIST)
+        list(JOIN DEPENDENCY_LIST "\n" DEPENDENCY_LINES)
+    else()
+        set(DEPENDENCY_LINES "")
+    endif()
+    
+    set(${OUTPUT_VAR} "${DEPENDENCY_LINES}" PARENT_SCOPE)
+endfunction()
+
 # Configures CMake install rules for library target and package config files.
 # - Precondition: NAME, PACKAGE_NAME, VERSION, and NAMESPACE specified; target NAME exists
 # - Postcondition: install rules created for target, config files, and export with NAMESPACE:: prefix
@@ -65,6 +117,9 @@ function(_cpp_library_setup_install)
         )
     endif()
 
+    # Generate find_dependency() calls for package dependencies
+    _cpp_library_generate_dependencies(PACKAGE_DEPENDENCIES ${ARG_NAME} ${ARG_NAMESPACE})
+    
     # Generate package version file
     # Uses SameMajorVersion compatibility (e.g., 2.1.0 is compatible with 2.0.0)
     write_basic_package_version_file(
@@ -74,6 +129,7 @@ function(_cpp_library_setup_install)
     )
 
     # Generate package config file from template
+    # PACKAGE_DEPENDENCIES will be substituted via @PACKAGE_DEPENDENCIES@
     configure_file(
         "${CPP_LIBRARY_ROOT}/templates/Config.cmake.in"
         "${CMAKE_CURRENT_BINARY_DIR}/${ARG_PACKAGE_NAME}Config.cmake"

templates/Config.cmake.in

@@ -3,4 +3,7 @@
 
 include(CMakeFindDependencyMacro)
 
-include("${CMAKE_CURRENT_LIST_DIR}/@[email protected]")
+# Find dependencies required by this package
+@PACKAGE_DEPENDENCIES@
+
+include("${CMAKE_CURRENT_LIST_DIR}/@[email protected]")