Optional .a linkage for libraries

[NicoHood]

Fixes:
#2800
#3649
And adds the possibility to create more enhanced libraries with smaller flash size. This feature is optional and won't break any existing library.

All you need to do is add a alinkage=true to your library.properties file. By default alinkage is off, to not break older libraries with ISRs. A linkage is only possible for newer libraries with a /src folder.

Most of the code was adapted from here, so it should work fine, I did not reinvent the wheel here.
https://github.com/arduino/Arduino/blob/master/arduino-core/src/processing/app/debug/Compiler.java#L1130-L1182

The code now moved in its own function (2nd commit) to reduce code duplication.

I am still not sure if we need recursiveCompileFilesInFolder() or if we can use compileFiles() with true as paramter. If desired I can add a new recursiveCompileFilesInFolder() which returns a List of Files instead of void, if that helps in any case. What was the thought behind this? For this PR it is not critical since .a linkage is optional and won't break anything, and the core compiling stays the same.

[matthijskooijman]

@ArduinoBot build this please.

[NicoHood]

No you need to write @ArduinoBot, Build this please without the dot :D

[ArduinoBot]

Build successful. Please test this code using one of the following:
http://downloads.arduino.cc/javaide/pull_requests/arduino-PR-3697-BUILD-386-linux32.tar.xz
http://downloads.arduino.cc/javaide/pull_requests/arduino-PR-3697-BUILD-386-linux64.tar.xz
http://downloads.arduino.cc/javaide/pull_requests/arduino-PR-3697-BUILD-386-windows.zip
http://downloads.arduino.cc/javaide/pull_requests/arduino-PR-3697-BUILD-386-macosx.zip

[cmaglie]

@ArduinoBot build this please

[cmaglie]

BTW the proposed patch looks good to me (y).

[NicoHood]

The easiest thing would be to merge it ;)
I've been using this for quite a while now and it works perfectly with and without .a linkage.

[matthijskooijman]

I haven't gotten around to looking at the patch in detail yet, should be able to do that in 1, max 2 weeks from now.

[ArduinoBot]

Build successful. Please test this code using one of the following:
http://downloads.arduino.cc/javaide/pull_requests/arduino-PR-3697-BUILD-388-linux32.tar.xz
http://downloads.arduino.cc/javaide/pull_requests/arduino-PR-3697-BUILD-388-linux64.tar.xz
http://downloads.arduino.cc/javaide/pull_requests/arduino-PR-3697-BUILD-388-windows.zip
http://downloads.arduino.cc/javaide/pull_requests/arduino-PR-3697-BUILD-388-macosx.zip

[matthijskooijman]

Seems this patch should be re-done for the new arduino-builder, now. @ffissore, any plans to include this? @NicoHood, care to learn the Go language too? :-)

[NicoHood]

If you tell me the files I need to have a look at after the change :S I dont care if its go, java or c.

But it should be easy for @ffissore to include this since he just wrote the compiler. So he knows where to search and how to add it best.

This seems promising:
https://github.com/arduino/arduino-builder/blob/master/src/arduino.cc/builder/libraries_loader.go
https://github.com/arduino/arduino-builder/tree/master/src/arduino.cc/builder/phases
https://github.com/arduino/arduino-builder/blob/master/src/arduino.cc/builder/builder_utils/utils.go

[NicoHood]

I've looked through the sources now and beside I do not fully get the Go language there is not a single commentary. So I am pretty much helpless here. I linked the useful files above but I am currently unable to understand how the .a linkage was used here. I also dont know how I should compile the files (the go files) anyways.

A bit feedback from @ffissore would be appreciated. Thanks.

[ffissore]

Closing as I'm working on it. Tracking issue is arduino/arduino-builder#10