Install header sets from CMake target property

Iterate over the target property for header sets to gather which
header sets are installed.
Extracted from
https://github.com/ClausKlein/exemplar/blob/feature/add_cxx_module/cmake/beman-install-library.cmake
and discussed in bemanproject/infra#19

Author: steve-downey

.pre-commit-config.yaml

@@ -4,37 +4,37 @@ repos:
   - repo: https://github.com/pre-commit/pre-commit-hooks
     rev: v6.0.0
     hooks:
-    -   id: trailing-whitespace
-    -   id: end-of-file-fixer
-    -   id: check-yaml
-    -   id: check-added-large-files
+      - id: trailing-whitespace
+      - id: end-of-file-fixer
+      - id: check-yaml
+      - id: check-added-large-files
 
-    # Clang-format for C++
-    # This brings in a portable version of clang-format.
-    # See also: https://github.com/ssciwr/clang-format-wheel
+  # Clang-format for C++
+  # This brings in a portable version of clang-format.
+  # See also: https://github.com/ssciwr/clang-format-wheel
   - repo: https://github.com/pre-commit/mirrors-clang-format
     rev: v21.1.8
     hooks:
-    - id: clang-format
-      types_or: [c++, c]
+      - id: clang-format
+        types_or: [c++, c]
 
-    # CMake linting and formatting
+  # CMake linting and formatting
   - repo: https://github.com/BlankSpruce/gersemi
     rev: 0.26.0
     hooks:
-    - id: gersemi
-      name: CMake linting
+      - id: gersemi
+        name: CMake linting
 
-    # Markdown linting
-    # Config file: .markdownlint.yaml
+  # Markdown linting
+  # Config file: .markdownlint.yaml
   - repo: https://github.com/igorshubovych/markdownlint-cli
     rev: v0.47.0
     hooks:
-    - id: markdownlint
-      args: ['--disable', 'MD013', ' --']
-      exclude: ^papers/
+      - id: markdownlint
+        args: ['--disable', 'MD013', ' --']
+        exclude: ^papers/
 
-    # Config file: .codespell_ignore
+  # Config file: .codespell_ignore
   - repo: https://github.com/codespell-project/codespell
     rev: v2.4.1
     hooks:

infra/cmake/beman-install-library-config.cmake

@@ -38,7 +38,8 @@ function(beman_install_library name)
     #
     set(options "")
     set(multiValueArgs "")
-    set(multiValueArgs "FILE_SET")
+    set(multiValueArgs TARGETS)
+
     cmake_parse_arguments(
         BEMAN_INSTALL_LIBRARY
         "${options}"
@@ -51,8 +52,11 @@ function(beman_install_library name)
         message(FATAL_ERROR "Target '${name}' does not exist.")
     endif()
 
-    if(NOT BEMAN_INSTALL_LIBRARY_FILE_SET)
-        set(BEMAN_INSTALL_LIBRARY_FILE_SET "HEADERS")
+    if(NOT BEMAN_INSTALL_LIBRARY_TARGETS)
+      if(NOT TARGET "${name}")
+        message(FATAL_ERROR "Target '${name}' does not exist and TARGETS not specified.")
+      endif()
+      set(BEMAN_INSTALL_LIBRARY_TARGETS ${name})
     endif()
 
     # Given foo.bar, the component name is bar
@@ -66,23 +70,56 @@ function(beman_install_library name)
         )
     endif()
 
-    set(target_name "${name}")
-    set(install_component_name "${name}")
-    set(export_name "${name}")
-    set(package_name "${name}")
-    list(GET name_parts -1 component_name)
-
-    install(
+    foreach(_tgt IN LISTS BEMAN_INSTALL_LIBRARY_TARGETS)
+      if(NOT TARGET "${_tgt}")
+        message(
+          WARNING
+          "beman_install_library(${name}): '${_tgt}' is not a target"
+        )
+        continue()
+      endif()
+
+      set(target_name "${_tgt}")
+      set(install_component_name "${_tgt}")
+      set(export_name "${name}")
+      set(package_name "${name}")
+      list(GET name_parts -1 component_name)
+
+      set(_install_header_set_args)
+      get_target_property(
+        _available_header_sets
+        ${_tgt}
+        INTERFACE_HEADER_SETS
+      )
+      if(_available_header_sets)
+        message(
+          VERBOSE
+          "beman-install-library(${name}): '${_tgt}' has INTERFACE_HEADER_SETS=${_available_header_sets}"
+        )
+        foreach(_install_header_set IN LISTS _available_header_sets)
+          list(
+            APPEND _install_header_set_args
+            FILE_SET
+            "${_install_header_set}"
+            COMPONENT
+            "${install_component_name}"
+          )
+        endforeach()
+      else()
+        set(_install_header_set_args FILE_SET HEADERS)
+      endif()
+
+      install(
         TARGETS "${target_name}"
-        COMPONENT "${install_component_name}"
         EXPORT "${export_name}"
-        FILE_SET "${BEMAN_INSTALL_LIBRARY_FILE_SET}"
-    )
+        ${_install_header_set_args}
+      )
 
-    set_target_properties(
+      set_target_properties(
         "${target_name}"
         PROPERTIES EXPORT_NAME "${component_name}"
-    )
+      )
+    endforeach()
 
     include(GNUInstallDirs)
 
@@ -129,10 +166,7 @@ function(beman_install_library name)
         find_file(
             config_file_template
             NAMES "${package_name}-config.cmake.in"
-            PATHS
-                "${CMAKE_CURRENT_SOURCE_DIR}"
-                "${PROJECT_SOURCE_DIR}/cmake"
-                "${CMAKE_SOURCE_DIR}/cmake"
+            PATHS "${PROJECT_SOURCE_DIR}/cmake"
             NO_DEFAULT_PATH
             NO_CACHE
             REQUIRED