feat: full support for features and profiles

[perazz]

This PR implements comprehensive Features and Profiles support, enabling conditional compilation, platform-specific configurations, and dependency feature propagation.

Overview

This implementation adds two major capabilities to FPM:

1. Features: Named sets of conditional build configurations that can be selectively enabled.
2. Profiles: Predefined combinations of features for common build scenarios

Key Features

✅ Feature System

• Complete control: Features are complete representations of an fpm manifest, allowing full customization
• Platform/compiler targeting: Features can be scoped to specific platforms or compilers:

[features]
my_feat.flag = ["-O3"] # Always applied
my_feat.gfortran.flag = ["-123"] # gfortran only, all OSes
my_feat.windows.flag = ["-DWIN32"] # all compilers, Windows-only
my_feat.macos.ifx.flag = ["..."] #
my_feat.ifx.macos.flag = ["..."] # specific compiler/OS combinations

• Conditional compilation: Enable/disable code paths with preprocessor macros.
• Compiler flags: Add feature-specific compilation flags
• Dependencies: Conditionally include dependencies based on active features

[features]
with_mpi.dependencies.mpi = ["*"]
with_mpi.preprocess.cpp.macros = ["HAVE_MPI"]

• Dependency feature propagation: Pass features to dependencies

[dependencies]
# Request fortran-regex with optional `mpi` feature enabled
fortran-regex = { git="https://github.com/perazz/fortran-regex", tag="1.1.2", features = ["mpi"]}

✅ Profile System

• Predefined configurations: Named combinations of features (e.g., development = ["debug","with_blas"])
• Default profiles: Built-in debug and release profiles (backward compatible; can be overridden)
• CLI integration: --profile <name> and --features <list> command line options

[features]
parallel_cpu.dependencies.mpi = "*"
parallel_cpu.dependencies.openmp = "*"
gpu_support.macos.flags = ["-framework OpenCL"]
gpu_support.unix.link = ["OpenCL"]
[profiles]
parallel = ["parallel_cpu", "gpu_support"]

✅ Advanced Capabilities

• Nested targeting: feature.os or feature.compiler or feature.compiler.os or feature.os.compiler syntax for fine-grained control
• Dependency features: Specify which features to enable in dependencies
• Preprocessing integration: CPP macro definitions and conditional compilation
• Validation: Comprehensive error checking for invalid feature/profile combinations

Usage Examples

Basic Feature Definition

[features]
debug.flags = "-g"
debug.preprocess.cpp.macros = "DEBUG"

release.flags = "-O3"
release.preprocess.cpp.macros = "RELEASE"

#  Platform/Compiler Specific Features

[features]
debug.gfortran.flags = "-Wall -fcheck=bounds"
debug.linux.preprocess.cpp.macros = "LINUX_BUILD"

#Dependency Features

[features]
mpi_support.dependencies.mpi_lib = { version = "*", features = ["parallel"] }

# Profiles

[profiles]
development = ["debug"]
production = ["release", "openmp"]

CLI Usage

Enable specific features

  fpm run --features debug,openmp

Use a profile

  fpm run --profile development

Build with dependency features

fpm build --features mpi_support

Backward Compatibility

• ✅ Fully backward compatible: Existing fpm.toml files work unchanged
• ✅ Default behavior preserved: No features => define default debug and release features and profiles
• ✅ Optional sections: [features] and [profiles] sections are completely optional

Testing

• Core implementation + comprehensive tests
• Integration tests: Multi-platform CI testing via ci/test_features.sh
• Unit tests: Feature parsing, validation, and merging
• Example packages: Real-world usage demonstrations
• CLI tests: Command-line interface validation

This implementation provides a solid foundation for conditional compilation and advanced build configurations in FPM while maintaining full backward compatibility with existing projects.

[Copilot]

Pull Request Overview

This PR implements comprehensive features and profiles support for FPM, enabling conditional compilation, platform-specific configurations, and dependency feature propagation. The implementation adds two major capabilities: features (named sets of conditional build configurations) and profiles (predefined combinations of features).

Key changes include:

• Complete feature system with platform/compiler targeting and conditional compilation
• Profile system for predefined feature combinations
• Dependency feature propagation and specification
• Command-line integration with --features and --profile options

Reviewed Changes

Copilot reviewed 30 out of 30 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/fpm_command_line.f90	Adds --features CLI option parsing and validation
src/fpm/manifest/profiles.f90	Implements new profile configuration system
src/fpm/manifest/feature_collection.f90	Adds feature merging, validation, and duplicate checking
test files	Updates and adds comprehensive test coverage
example packages	Demonstrates feature and profile functionality

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