Library Dependency Finder (LDF)

Library Dependency Finder is a core part of PlatformIO Build System that operates with the C/C++ source files and looks for #include ... directives to know what header directories to include for the compiler.

In spite of the fact that Library Dependency Finder is written in pure Python, it evaluates C/C++ Preprocessor conditional syntax (#ifdef, if, defined, else, and elif) without calling gcc -E. This approach allows to significantly reduce the total compilation time. See Dependency Finder Mode for more details.

Storage

There are different storages where Library Dependency Finder looks for libraries. These storages (folders) have priority and LDF operates in the next order:

  1. lib_extra_dirs - extra storages per build environment
  2. lib_dir - own/private library storage per project
  3. libdeps_dir - project dependency storage used by Library Manager
  4. “core_dir/lib” - global storage per all projects.
  5. Library storages built into frameworks, SDKs.

Dependency Finder Mode

Library Dependency Finder starts work from analyzing source files of the project (src_dir) and can work in the next modes:

off:“Manual mode”, does not process source files of a project and dependencies. Builds only the libraries that are specified in manifests (library.json, module.json) or using lib_deps option.
chain:[DEFAULT] Parses ALL C/C++ source files of the project and follows only by nested includes (#include ..., chain…) from the libraries. It also parses C, CC, CPP files from libraries which have the same name as included header file. Does not evaluate C/C++ Preprocessor conditional syntax.
deep:Parses ALL C/C++ source files of the project and parses ALL C/C++ source files of the each found dependency (recursively). Does not evaluate C/C++ Preprocessor conditional syntax.
chain+:The same behavior as for the chain but evaluates C/C++ Preprocessor conditional syntax.
deep+:The same behavior as for the deep but evaluates C/C++ Preprocessor conditional syntax.

The mode can be changed using lib_ldf_mode option in “platformio.ini” (Project Configuration File). Default value is set to chain.

Note

Usually, when the LDF appears to fail to identify a dependency of a library, it is because the dependency is only referenced from a library source file, and not a library header file (see example below). In this case, it is necessary to either explicitly reference the dependency from the project source or “platformio.ini” (Project Configuration File) (lib_deps option), or change the LDF mode to “deep” (not generally recommended).

A difference between chain/chain+ and deep/deep+ modes. For example, there are 2 libraries:

  • Library Foo with files:
    • Foo/foo.h
    • Foo/foo.cpp
    • Foo/extra.cpp
  • Library Bar with files:
    • Bar/bar.h
    • Bar/bar.cpp
Case 1:
  • lib_ldf_mode = chain
  • Foo/foo.h depends on the Bar library (contains #include <bar.h>)
  • #include <foo.h> is located in one of the project source files

Here the nested includes (project file > foo.h > bar.h) and LDF will find both libraries “Foo`` and Bar.
Case 2:
  • lib_ldf_mode = chain
  • Foo/extra.cpp depends on the Bar library (contains #include <bar.h>)
  • #include <foo.h> is located in one of the project source files

In this case, LDF will not find the Bar library because it doesn’t know about the CPP file (Foo/extra.cpp).
Case 3:
  • lib_ldf_mode = deep
  • Foo/extra.cpp depends on Bar library (contains #include <bar.h>)
  • #include <foo.h> is located in one of the project source files

Firstly, LDF finds the Foo library, then it parses all sources from the Foo library and finds Foo/extra.cpp that depends on #include <bar.h>. Secondly, it will parse all sources from the Bar library. This operation continues until all dependencies will not be parsed.

Compatibility Mode

Compatibility mode allows one to control strictness of Library Dependency Finder. If library contains one of manifest file (library.json, library.properties, module.json), then LDF check compatibility of this library with real build environment. Available compatibility modes:

off:Does not check for compatibility (is not recommended)
soft:[DEFAULT] Checks for the compatibility with framework from build environment
strict:Checks for the compatibility with framework and platform from build environment.

This mode can be changed using lib_compat_mode option in “platformio.ini” (Project Configuration File). Default value is set to soft.

C/C++ Preprocessor conditional syntax

In spite of the fact that Library Dependency Finder is written in pure Python, it evaluates C/C++ Preprocessor conditional syntax (#ifdef, if, defined, else, and elif) without calling gcc -E. For example,

platformio.ini

[env:myenv]
lib_ldf_mode = chain+
build_flags = -D MY_PROJECT_VERSION=13

mylib.h

#ifdef PROJECT_VERSION
// include common file for the project
#include "my_common.h"
#endif

#if PROJECT_VERSION < 10
// this include will be ignored because does not satisfy condition above
#include "my_old.h"
#endif