Library Dependency Finder is a core part of PlatformIO Build System that
operates with the C/C++ source files and looks for #include ...
directives.
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
significantly reduce total compilation time. See Dependency Finder Mode for more
details.
Library Dependency Finder can be configured from “platformio.ini” (Project Configuration File):
There are different storages where Library Dependency Finder looks for libraries. These storages (folders) have priority and LDF operates in the next order:
lib_extra_dirs - extra storages per build environment
lib_dir - own/private library storage per project
libdeps_dir - project dependency storage used by Library Manager
“core_dir/lib” - global storage per all projects.
Library storages built into frameworks, SDKs.
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 the library source file, and not the 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
lib_ldf_mode = chain
Foo/foo.h depends on “Bar” library (contains #include <bar.h>)
#include <foo.h> is located in one of the project source files
Here are nested includes (project file > foo.h > bar.h) and LDF
will find both libraries “Foo” and “Bar”.
lib_ldf_mode = chain
Foo/extra.cpp depends on “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 “Bar” library because it doesn’t know
about CPP file (Foo/extra.cpp).
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 “Foo” library, then it parses all sources from “Foo”
library and finds Foo/extra.cpp that depends on #include <bar.h>.
Secondly, it will parse all sources from “Bar” library and this operation
continues until all dependencies will not be parsed.
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.
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