Restructure CMake Build System to Follow Modern Best Practices

[Samiisd]

Restructure CMake Build System to Follow Modern Best Practices

Problem

The current yaml-cpp build system has several issues:

1. It uses file(GLOB ...) for finding source files, which:

   • Forces CMake to scan the filesystem during each configuration run
   • Makes builds non-deterministic
   • Doesn't detect new files automatically until reconfiguration
   • Slows down configuration, especially in large projects

2. The build system structure doesn't follow modern CMake organization:

   • All build logic is in a single monolithic CMakeLists.txt
   • Library targets, source files, and properties are defined in the root file
   • Lacks proper modularization, making maintenance challenging

Solution

This MR implements a proper hierarchical CMake structure that:

1. Follows modern CMake best practices:

   • Moves library target definition to src/CMakeLists.txt
   • Moves source file management to the directories where files are located
   • Uses proper add_subdirectory() approach instead of globbing
   • Explicitly lists source files for better control and determinism

2. The structure establishes clear responsibilities:

   • Root CMakeLists.txt: Project configuration, options, and installation
   • src/CMakeLists.txt: Library definition, core source files, properties
   • src/contrib/CMakeLists.txt: Contrib module source files

Benefits

• Improved Build Performance: Eliminates slow filesystem scanning during configuration
• Deterministic Builds: Source files are explicitly listed, not dynamically discovered
• Better Scalability: Adding new source directories is simple with this structure
• Clearer Organization: Build logic is located close to the source files it manages
• Easier Maintenance: Each component manages its own sources
• Easier Integration: Better compatibility with build systems that cache configurations
• Follows Best Practices: Aligns with modern CMake recommendations

Implementation Details

The implementation follows a carefully structured approach:

1. Root CMakeLists.txt:

   • Defines project, options, and configuration settings
   • Uses add_subdirectory(src) to delegate library building
   • Handles installation and packaging

2. src/CMakeLists.txt:

   • Creates the library target (add_library(yaml-cpp))
   • Sets library properties and compile options
   • Lists all core source files explicitly
   • Adds the contrib subdirectory

3. src/contrib/CMakeLists.txt:

   • Lists all contrib source files explicitly
   • Adds them to the main target conditionally based on options

The provided script can automatically generate this structure from an existing yaml-cpp repository.

Notes for Maintainers

With this new structure:

• New source files should be added to the CMakeLists.txt in their directory
• New source directories would add their own CMakeLists.txt and be included via add_subdirectory()
• The structure can easily scale to more complex organization as the library grows