Building a library without linking attempt

[matthiashanns]

Problem

Library projects contain their sources in src/ and include/ and don't have a main() function. Building such a project first compiles the code and subsequently tries to link it unnecessarily. The linker, however, fails by complaining about a missing main() or missing setup() and loop() (depending on whether, e.g., the arduino framework is in use).

There is no project parameter in platformio.ini to tell pio not to link a library project. There is also no build parameter to the compiler (eg. gcc) to suppress the linker since the linker is started exclusively by pio. A custom build script could be used, but it should not be required for a common task like building a library project.

Expected behavior

Building a library project should contain the steps of compiling, optionally creating a library archive (.a), and optionally including an archive index, but no linking step.

• A project should be markable as a library project in platformio.ini (eg. type = library with type defaulting to application) to omit the linking step and avoid a linking error and hence a build error.
• Additionally, a compile-only build option should exist that compiles without linking to quickly build a library project or check the code for compile errors on any project, saving the linker time.