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mergerfs - AGENTS.md

This file contains build commands, testing procedures, and code style guidelines for agentic coding assistants working in this repository.

# Build project
make

# Build tests
make tests

# Clean build artifacts
make clean

# Build with specific options
make USE_XATTR=0      # Build without xattr support
make STATIC=1         # Build static binary
make LTO=1            # Enable link-time optimization

# Build with debugging and sanitizers
make NDEBUG= SANITIZE=1

# Install
make install

Unit Tests (C++)

# Build tests
make tests

# Run all unit tests
./build/tests <test_name>
# Example: ./build/tests config_bool

# Run all tests via acutest framework
./build/tests

Integration Tests (Python)

# Build the main binary first
make

# Run all integration tests
./tests/run-tests <path-to-mergerfs-binary>
# Example: ./tests/run-tests ./build/mergerfs

# Run a single integration test directly
./tests/TEST_unlink_rename <path-to-mergerfs-binary>

Code Style Guidelines

File Organization

Source files: src/*.cpp
Header files: src/*.hpp
Tests: tests/*.cpp (unit), tests/TEST_* (integration)
Build: Makefile (no build system generators)

License Headers

Every source file MUST start with the full ISC license header:

/*
  ISC License

  Copyright (c) YEAR, Antonio SJ Musumeci <trapexit@spawn.link>

  Permission to use, copy, modify, and/or distribute this software for any
  purpose with or without fee is hereby granted, provided that the above
  copyright notice and this permission notice appear in all copies.

  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  OR CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/

Include Guards and Ordering

Use #pragma once for header guards. Organize includes as:

#include "local_header.hpp"   // Local headers first
#include <system_header>      // Then system headers

#include <system_headers.h>   // C headers last, if needed

Naming Conventions

Classes: PascalCase (e.g., Branches, Config, Policy)
Functions/methods: snake_case (e.g., minfreespace(), from_string())
Variables: snake_case (e.g., branches_, fusepath_)
Private members: _prefix (e.g., _impl, _mutex)
Constants/macros: SCREAMING_SNAKE_CASE (e.g., MINFREESPACE_DEFAULT)
Namespaces: PascalCase for major namespaces, lowercase for utilities (e.g., Policy, fs, str)

Indentation and Formatting

Indentation: 2 spaces
Brace style: K&R style
Line length: No strict limit, but keep readable (~80-100 chars preferred)
No trailing whitespace

namespace Policy
{
  class ActionImpl
  {
  public:
    ActionImpl(const std::string &name_)
      : name(name_)
    {
    }

  public:
    std::string name;
    virtual int operator()(...) const = 0;
  };
}

Types and Type Safety

Language: C++17 (-std=c++17)
Use standard types: int, uint64_t, size_t, etc.

Custom typedefs: Use typedef for common configuration types:

typedef ToFromWrapper<bool> ConfigBOOL;
typedef ToFromWrapper<uint64_t> ConfigUINT64;

Smart pointers: Use std::shared_ptr, std::unique_ptr appropriately

Error Handling

Return values: Functions return 0 for success, negative errno for errors
System call errors: Return negative errno (e.g., -EACCES, -ENOENT)
Error propagation: Keep negative errno values through the call stack

int
fs::some_function(const fs::path &path_)
{
  int rv = ::actual_syscall(path_);
  if(rv < 0)
    return -errno;
  return rv;
}

Use the error_and_continue() macro for policy error handling:

#define error_and_continue(CUR,ERR) \
  {                                 \
    policy::calc_error(CUR,ERR);    \
    continue;                       \
  }

Functions and Methods

Static helpers: Prefix with _ when file-local (e.g., _helper_function())
Namespaces: Explicitly use namespace qualifiers for organization
Parameters: Pass by const reference for complex types, by value for simple types
Output parameters: Use pointers or references

static
int
_helper_function(const Branches::Ptr  &branches_,
                std::vector<Branch*> &paths_)
{
  // Implementation
  return 0;
}

namespace FUSE
{
  int
  open(const fuse_req_ctx_t *ctx,
       const char           *fusepath,
       fuse_file_info_t     *ffi);
}

Testing Style

Unit tests (C++) use the Acutest framework:

void
test_config_bool()
{
  ConfigBOOL v;

  TEST_CHECK(v.from_string("true") == 0);
  TEST_CHECK(v == true);
  TEST_CHECK(v.to_string() == "true");

  TEST_CHECK(v.from_string("false") == 0);
  TEST_CHECK(v == false);
  TEST_CHECK(v.to_string() == "false");

  TEST_CHECK(v.from_string("asdf") == -EINVAL);
}

TEST_LIST =
  {
   {"config_bool",test_config_bool},
   {NULL,NULL}
  };

Integration tests (Python) are scripts prefixed with TEST_ that test specific filesystem behaviors.

Compiler Warnings

The Makefile uses strict warnings with -Werror for:

-Wpessimizing-move / -Werror=pessimizing-move
-Wredundant-move / -Werror=redundant-move
-Wall, -Wextra, -Wno-unused-result, -Wno-unused-parameter

Code must compile without warnings.

Version Notes

Only tagged releases are officially supported
master and other branches are works in progress
Always ensure code compiles and tests pass before submitting changes

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