Does not rely on CMake's FindBoost module.

CMakeLists.txt

@@ -9,14 +9,20 @@ if (${CMAKE_VERSION} VERSION_GREATER_EQUAL "3.13")
     cmake_policy(SET CMP0077 NEW)
 endif ()
 
+# When using the URL download method with the ExternalProject_Add() or
+# FetchContent_Declare() commands, sets the timestamps of extracted contents
+# to the time of extraction.
 if (${CMAKE_VERSION} VERSION_GREATER_EQUAL "3.24")
     cmake_policy(SET CMP0135 NEW)
 endif ()
 
+# Accept <PACKAGENAME>_ROOT variables for find_package() command.
 if (${CMAKE_VERSION} VERSION_GREATER_EQUAL "3.27")
     cmake_policy(SET CMP0144 NEW)
 endif ()
 
+# find_package(Boost) to search for the upstream BoostConfig.cmake.
+# Disable CMake's FindBoost module.
 if (${CMAKE_VERSION} VERSION_GREATER_EQUAL "3.30")
     cmake_policy(SET CMP0167 NEW)
 endif ()
@@ -196,15 +202,13 @@ if (PRIVATEER_ROOT)
 endif ()
 
 # ---------- Boost ---------- #
-find_package(Boost 1.80)
+include(find_boost_headers)
+find_boost_headers(1.80 FALSE)
 if (NOT Boost_FOUND)
-    message(STATUS "Boost is not found. Fetching Boost.")
+    message(STATUS "Fetching Boost")
     FetchContent_Declare(Boost
             URL https://boostorg.jfrog.io/artifactory/main/release/1.83.0/source/boost_1_83_0.tar.bz2)
-    FetchContent_GetProperties(Boost)
-    if (NOT Boost_POPULATED)
-        FetchContent_Populate(Boost)
-    endif ()
+    FetchContent_MakeAvailable(Boost)
     set(BOOST_ROOT ${boost_SOURCE_DIR})
     find_package(Boost 1.80 REQUIRED)
 endif ()

cmake/find_boost_headers.cmake

@@ -0,0 +1,60 @@
+# Find Boost header files
+# Input:
+#   min_version - minimum required Boost version
+#   required - if TRUE, the function will stop the build if Boost headers are not found
+#
+#  This function first tries to find Boost headers using the find_package() command.
+#  If Boost headers are not found, the function tries to find Boost headers manually.
+#  In the case, the following variables as hints to find Boost headers, in the following order:
+#   BOOST_ROOT  CMake variable, Boost_ROOT CMake variable, BOOST_ROOT environment variable, Boost_ROOT environment variable
+#
+# Output:
+#   Boost_FOUND - TRUE if Boost headers are found
+#   Boost_INCLUDE_DIRS - Boost header files directory
+#   Boost_VERSION - Boost version
+function(find_boost_headers min_version required)
+    find_package(Boost ${min_version})
+    if (Boost_FOUND)
+        set(Boost_INCLUDE_DIRS ${Boost_INCLUDE_DIRS} PARENT_SCOPE)
+        set(Boost_FOUND ${Boost_FOUND} PARENT_SCOPE)
+        return()
+    endif ()
+
+    message(STATUS "Could not find Boost headers using the find_package() command. Trying to find Boost headers manually.")
+
+    # Try to find Boost headers manually using the BOOST_ROOT as a hint
+    find_path(Boost_INCLUDE_DIRS boost/version.hpp PATHS ${BOOST_ROOT} ${Boost_ROOT} $ENV{BOOST_ROOT} $ENV{Boost_ROOT} NO_DEFAULT_PATH)
+    if (Boost_INCLUDE_DIRS)
+
+        # Extract Boost version value from the boost/version.hpp file
+        file(STRINGS ${Boost_INCLUDE_DIRS}/boost/version.hpp _boost_version REGEX "#define BOOST_VERSION[ \t]+[0-9]+")
+        string(REGEX REPLACE "#define BOOST_VERSION[ \t]+([0-9]+)" "\\1" Boost_VERSION ${_boost_version})
+
+        # Convert Boost version to the format 'MAJOR.MINOR.PATCH'
+        # Major version
+        math(EXPR Boost_VERSION_MAJOR "${Boost_VERSION} / 100000")
+        # Minor version
+        math(EXPR Boost_VERSION_MINOR "(${Boost_VERSION} / 100) % 1000")
+        # Patch version
+        math(EXPR Boost_VERSION_PATCH "${Boost_VERSION} % 100")
+        set(Boost_VERSION "${Boost_VERSION_MAJOR}.${Boost_VERSION_MINOR}.${Boost_VERSION_PATCH}")
+
+        if (${Boost_VERSION} VERSION_GREATER_EQUAL ${min_version})
+            message(STATUS "Found Boost headers at ${Boost_INCLUDE_DIRS}")
+            message(STATUS "Boost version: ${Boost_VERSION}")
+            set(Boost_FOUND TRUE PARENT_SCOPE)
+            set(Boost_INCLUDE_DIRS ${Boost_INCLUDE_DIRS} PARENT_SCOPE)
+            set(Boost_VERSION ${Boost_VERSION} PARENT_SCOPE)
+            return()
+        else ()
+            message(WARNING "Found an old Boost version '${Boost_VERSION}'. Required version is '${min_version}'.")
+        endif ()
+    endif ()
+
+    # Not found
+    set(Boost_FOUND FALSE PARENT_SCOPE)
+    if (required)
+        message(FATAL_ERROR "Could not find Boost headers")
+    endif ()
+
+endfunction()