Set CPM_SOURCE_CACHE in CMake presets and update docs

Moved CPM_SOURCE_CACHE configuration from CMakeLists.txt to CMakePresets.json for all presets, ensuring consistent and automatic cache setup. Updated README to document this behavior and removed redundant cache setup code from setup.cmake and README.

Author: sean-parent

README.md

@@ -101,11 +101,6 @@ Use `CPMAddPackage` to fetch cpp-library directly in your `CMakeLists.txt`:
 ```cmake
 cmake_minimum_required(VERSION 3.24)
 
-# Setup CPM cache before project()
-if(PROJECT_IS_TOP_LEVEL AND NOT CPM_SOURCE_CACHE AND NOT DEFINED ENV{CPM_SOURCE_CACHE})
-    set(CPM_SOURCE_CACHE "${CMAKE_SOURCE_DIR}/.cache/cpm" CACHE PATH "CPM source cache")
-    message(STATUS "Setting cpm cache dir to: ${CPM_SOURCE_CACHE}")
-endif()
 include(cmake/CPM.cmake)
 
 # Fetch cpp-library before project()
@@ -426,6 +421,8 @@ cpp-library generates a `CMakePresets.json` file with the following configuratio
 - **`clang-tidy`**: Static analysis build
 - **`init`**: Template regeneration (regenerates CMakePresets.json, CI workflows, etc.)
 
+All presets automatically configure `CPM_SOURCE_CACHE` to `${sourceDir}/.cache/cpm` for faster dependency resolution. You can override this by setting the `CPM_SOURCE_CACHE` environment variable.
+
 ### Version Management
 
 Version is automatically detected from git tags:

setup.cmake

@@ -314,11 +314,6 @@ endif()
 file(WRITE "${PROJECT_DIR}/CMakeLists.txt"
 "cmake_minimum_required(VERSION 3.24)
 
-# Setup CPM cache before project()
-if(PROJECT_IS_TOP_LEVEL AND NOT CPM_SOURCE_CACHE AND NOT DEFINED ENV{CPM_SOURCE_CACHE})
-    set(CPM_SOURCE_CACHE "${CMAKE_SOURCE_DIR}/.cache/cpm" CACHE PATH "CPM source cache")
-    message(STATUS "Setting cpm cache dir to: ${CPM_SOURCE_CACHE}")
-endif()
 include(cmake/CPM.cmake)
 
 # Fetch cpp-library before project()

templates/CMakePresets.json

@@ -11,7 +11,8 @@
         "CMAKE_BUILD_TYPE": "Release",
         "BUILD_TESTING": "OFF",
         "CMAKE_EXPORT_COMPILE_COMMANDS": "ON",
-        "CMAKE_CXX_EXTENSIONS": "OFF"
+        "CMAKE_CXX_EXTENSIONS": "OFF",
+        "CPM_SOURCE_CACHE": "${sourceDir}/.cache/cpm"
       }
     },
     {
@@ -24,7 +25,8 @@
         "CMAKE_BUILD_TYPE": "Debug",
         "BUILD_TESTING": "ON",
         "CMAKE_EXPORT_COMPILE_COMMANDS": "ON",
-        "CMAKE_CXX_EXTENSIONS": "OFF"
+        "CMAKE_CXX_EXTENSIONS": "OFF",
+        "CPM_SOURCE_CACHE": "${sourceDir}/.cache/cpm"
       }
     },
     {
@@ -38,7 +40,8 @@
         "BUILD_TESTING": "OFF",
         "BUILD_DOCS": "ON",
         "CMAKE_EXPORT_COMPILE_COMMANDS": "ON",
-        "CMAKE_CXX_EXTENSIONS": "OFF"
+        "CMAKE_CXX_EXTENSIONS": "OFF",
+        "CPM_SOURCE_CACHE": "${sourceDir}/.cache/cpm"
       }
     },
     {
@@ -52,7 +55,8 @@
         "BUILD_TESTING": "ON",
         "CMAKE_EXPORT_COMPILE_COMMANDS": "ON",
         "CMAKE_CXX_EXTENSIONS": "OFF",
-        "CMAKE_CXX_CLANG_TIDY": "clang-tidy"
+        "CMAKE_CXX_CLANG_TIDY": "clang-tidy",
+        "CPM_SOURCE_CACHE": "${sourceDir}/.cache/cpm"
       }
     },
     {
@@ -66,7 +70,8 @@
         "BUILD_TESTING": "OFF",
         "CMAKE_EXPORT_COMPILE_COMMANDS": "ON",
         "CMAKE_CXX_EXTENSIONS": "OFF",
-        "CPP_LIBRARY_FORCE_INIT": "ON"
+        "CPP_LIBRARY_FORCE_INIT": "ON",
+        "CPM_SOURCE_CACHE": "${sourceDir}/.cache/cpm"
       }
     }
   ],