[Buildroot] [PATCH] pkg-generic: Strip all but leading comments from C files used as license.

[Thomas Petazzoni <thomas.petazzoni@free-electrons.com>]

Dear Peter Rosin,

On Tue, 17 Nov 2015 18:02:19 +0100, Peter Rosin wrote:
> From: Peter Rosin <peda@axentia.se>
> 
> Signed-off-by: Peter Rosin <peda@axentia.se>

Thanks for your contribution. Could you explain what is the problem
with keeping a complete source file as legal information?

> diff --git a/package/pkg-utils.mk b/package/pkg-utils.mk
> index 44bd2c9..1497eb2 100644
> --- a/package/pkg-utils.mk
> +++ b/package/pkg-utils.mk
> @@ -145,8 +145,30 @@ endef
>  
>  define legal-license-file # pkg, filename, file-fullpath, {HOST|TARGET}
>  	$(call legal-license-header,$(1),$(2) file,$(4)) && \
> -	cat $(3) >>$(LEGAL_LICENSES_TXT_$(4)) && \
> -	echo >>$(LEGAL_LICENSES_TXT_$(4)) && \
>  	mkdir -p $(LICENSE_FILES_DIR_$(4))/$(1)/$(dir $(2)) && \
> -	cp $(3) $(LICENSE_FILES_DIR_$(4))/$(1)/$(2)
> +	case $(3) in \
> +	*.c|*.h) \
> +	  sed -e '\
> +x;\
> +/^$$/{\
> +  x;\
> +  /^[ \t]*$$/b;\
> +  /^[ \t]*\/\//b;\
> +  /^[ \t]*\/\*.*\*\//b;\
> +  /^[ \t]*\/\*/h;\
> +  //b;\
> +  s/.*//;\
> +  q\
> +};\
> +x;\
> +/\*\//{\
> +  x;\
> +  s/.*//;\
> +  x\
> +}' < $(3) > $(LICENSE_FILES_DIR_$(4))/$(1)/$(2) \

We quickly discussed your proposal on the #buildroot IRC, and the
conclusion is that we generally don't like this, for at least two
reasons:

 1/ The sed expression is awfully complicated.

 2/ There is absolutely no guarantee that the license part is inside
    the leading comment and that the complicated sed expression will
    actually keep the relevant part of the file.

We generally try to use a fairly short source code file as the license
text, so that keeping the entire file should not be a problem. If it
remains a problem, then I would suggest that you work with the upstream
project and ask them to include a separate license file that we can use.

Another possibility would be to do something like:

<pkg>_LICENSE_FILES = foo.c-23+42

to indicate that the license text is from line 23 to line 42. But it is
again not very foolproof, and it doesn't give much benefits.

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com