make: add snippets support

[kaspar030]

First try at #4290.

Whenever a module dir contains "NNname.c.snip" (with NN a decimal), the makefile concatenates that file with all other "NNname.c.snip" of other modules into $(BINDIR)/snippets/name.c and compiles all combined files into a "snippets" module.

For all but the application module, the snippets get enclosed by #ifdef MODULE_X ... #endif

That way, static array definitions, functions, ... can be spread over multiple files in all module directories.

Imagine shell commands, auto_init, saul parameters, device driver parameters, coap endpoints, .. can be defined by just adding a snippet where it belongs.

You've hooked up another radio (same as onboard) to your board? Just drop a file "01at86rf2xx_params.c.snip" into your application folder, containing only the array entry for the added device.

Your module auto_inits? Just drop a 01auto_init.c.snip into it's folder, no more rebase conflicts in sys/auto_init/auto_init.c.

What do you guys think?

[kaspar030]

I've changed xtimer's auto init to use snippets in order to show how this is supposed to be used.

[jnohlgard]

Couldn't you just use #include "01snip.c"... and so on?

[kaspar030]

@gebart Yes, much simpler.

[DipSwitch]

Nice one! :)

[kaspar030]

Fun thing to try:

# cd examples/hello-world
# echo 'puts("wooohooo!!");' > 10auto_init.c.snip
# make clean all term

[Kijewski]

I like the idea. 👍 Maybe add an underscore after the index for better readability?

[jnohlgard]

I have some thoughts regarding file names:

.c.snip will confuse many IDEs which set syntax highlighting based on *.c, is it possible to fix without getting them sucked into the normal build rules?

Since the name part of NNname.c.snip is what groups them together, would it make sense to change the pattern to nameNN.c.snip to also get the files grouped together when listing files alphabetically, in case there are multiple snips in the same directory?

[kaspar030]

.c.snip will confuse many IDEs which set syntax highlighting based on *.c, is it possible to fix without getting them sucked into the normal build rules?

I thought about that, it might be possible to use make filters filters if they're called something like *.snip.c. Then we'd have to create filter rules for all filetypes, currently this would probably also work with headers.

I'll look into it...

[kaspar030]

Since the name part of NNname.c.snip is what groups them together, would it make sense to change the pattern to nameNN.c.snip to also get the files grouped together when listing files alphabetically, in case there are multiple snips in the same directory?

good idea!

[kaspar030]

Ok, the snippets are now called <filename>.snipNN.ext.

@Kijewski I tried with a '_' between snip and number, but somehow I liked it better like this. What do you think?

[kaspar030]

I'll close this in favor of a linker-script based solution.