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.opencode/cmake-plan.md

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+# CMake 2026 Project Setup Plan
+
+## Overview
+This document outlines the technical plan for setting up a CMake-based C++ project with the following requirements:
+- clang++ compiler with C++23 defaults
+- Automatic source file discovery in src/ directory
+- Executable generation from files containing 'main' in filename
+- External dependency handling for git submodules
+- Organized compile flags and variables
+
+## Key Components
+
+### 1. Compiler Configuration
+- Use clang++ as the C++ compiler
+- Set C++ standard to C++23
+- Configure appropriate compiler flags for clang
+
+### 2. Source File Discovery
+- Scan src/ directory for all .cpp files
+- Use regex pattern `.*main.*\.cpp$` to identify main files
+- Separate main files from other source files
+
+### 3. Executable Generation
+- Automatically create executables from files with 'main' in filename
+- Create a library from all non-main source files
+- Link the library to each executable
+
+### 4. External Dependency Management
+- Handle dependencies in external/ directory
+- Example: spdlog in external/spdlog with namespace spdlog
+- Create interface libraries for external dependencies
+
+### 5. Compile Flags Organization
+- Debug build flags: -g -O0 -Wall -Wextra
+- Release build flags: -O3 -DNDEBUG -Wall -Wextra
+- Common flags: -std=c++23 -fPIC
+
+## Implementation Details
+
+### Regex Pattern
+```
+.*main.*\.cpp$
+```
+Used to detect files containing 'main' in their filename.
+
+### Directory Structure
+- `src/` - Source files directory
+- `external/` - Git submodules directory
+- `include/` - Header files directory
+
+### File Processing Logic
+1. Find all .cpp files in src/
+2. Separate main files from other source files
+3. Create library from non-main files
+4. Generate executables from main files
+5. Link library and external dependencies to each executable
+
+## CMake Commands Used
+- `cmake_minimum_required(VERSION 3.15)`
+- `project(ProjectEuler CXX)`
+- `file(GLOB_RECURSE)`
+- `list(APPEND)`
+- `add_executable()`
+- `add_library()`
+- `target_link_libraries()`
+- `target_compile_features()`
+- `find_package()`
+- `add_subdirectory()`