[OpenWrt-Devel] A note on selects vs. DEPENDS

[Daniel Dickinson]

I've run into a situation where that solution does not work.

Specifically:

   DEPENDS:=+PACKAGE_TAR_POSIX_ACL:libacl +PACKAGE_TAR_XATTR:libxattr 
+PACKAGE_TAR_BZIP2:bzip2 +PACKAGE_TAR_XZ:xz
endef

define Package/tar/config
         config PACKAGE_TAR_POSIX_ACL
         bool "tar: Enable POSIX ACL support" if PACKAGE_tar
         default y if USE_FS_ACL_ATTR
         default n

         config PACKAGE_TAR_XATTR
         bool "tar: Enable extended attribute (xattr) support" if 
PACKAGE_tar
         default y if USE_FS_ACL_ATTR
         default n

         config PACKAGE_TAR_GZIP
         bool "tar: Enable seamless gzip support" if PACKAGE_tar
         default y

         config PACKAGE_TAR_BZIP2
         bool "tar: Enable seamless bzip2 support" if PACKAGE_tar
         default y

         config PACKAGE_TAR_XZ
         bool "tar: Enable seamless xz support" if PACKAGE_tar
         select PACKAGE_xz
         default y
endef

That results in a circular dependency.

Using EXTRA_DEPENDS and select in config section is necessary because of 
the way package dependency parsing mangles the dependencies when using 
+PACKAGE_TAR_XZ:xz.  Specifically xz 'depends on' xz-utils in the xz 
package definition. When taken in combination with +PACKAGE_TAR_XZ:xz 
the parsing/mangling results in a recursive dependency where tar depends 
on PACKAGE_TAR_XZ and vice versa, because the recursive dependency 
checker does not distinguish between

depends on SYMBOL
vs.
depends on !SYMBOL

and the xz-utils depends results in

PACKAGE_tar depends on !(PACKAGE_TAR_XZ) || PACKAGE_xz-utils

and PACKAGE_TAR_XZ depends on PACKAGE_tar because it makes no sense 
without tar (and submenu doesn't work without the if PACKAGE_tar or a 
depends on PACKAGE_tar).


On 22/12/15 06:46 PM, Felix Fietkau wrote:
> On 2015-12-23 00:42, Daniel Dickinson wrote:
>> Hi Felix,
>>
>> On 22/12/15 09:03 AM, Felix Fietkau wrote:
>>> On 2015-12-22 06:02, Daniel Dickinson wrote:
>>>> Hi all,
>>>>
>>>> I just discovered something.  It seems that in a package if you have a
>>>> config section that does select PACKAGE_condition_dependency then the
>>>> build succeeds but when you do opkg install, opkg does not 'know' about
>>>> the dependency.
>>>>
>>>> That means if you have a situation like lldpd where you have a
>>>> conditional dependency it is not enough to add selects to same
>>>> config section as the conditional compilation flags, but you also need
>>>> to add an EXTRA_DEPENDS:=$(if
>>>> $(CONFIG_<conditional-compilation-flag>),conditional_dependency) line.
>>>>
>>>> I will be submitting a patch to lldpd with that fix, since my previous
>>>> patch fixed compilation, but doesn't solve the opkg problem (although no
>>>> one is likely to actually run across it because libjson-c is installed
>>>> by default so it's unlikely any failure would actually occur).  (Before
>>>> my patch even compilation would fail if json output was disable due to
>>>> missing dependency, now you would likely never notice the problem
>>>> because libjson-c is installed by default, but I discovered the issue in
>>>> reference to package to which I'm adding conditional build logic in the
>>>> packages feed for which the conditional dependency is not included
>>>> unless the package I'm working on depends on it).
>>> You should just use the normal conditional depends syntax for the
>>> DEPENDS line in the package, instead of duplicating it in Config.in and
>>> EXTRA_DEPENDS.
>>>
>>> DEPENDS:=+PACKAGE_conditional_package:selected_package
>>
>> It's actually used in the context of a Package/<pkg>/config section that
>> does some condition compilation option that when enabled adds another
>> dependency.  Hence the unusual method.  Conditional dependency based on
>> the configure option I had forgotten as an option though:
>>
>> i.e.
>>
>> config PACKAGE_LLDPD_JSON
>> bool "Enable JSON output"
>> default n
>>
>> and in depends
>>
>> DEPENDS:=PACKAGE_LLDPD_JSON:libjson-c
> DEPENDS:=+PACKAGE_LLDPD_JSON:libjson-c (the + turns it into a select).
> Then you don't need to select libjson-c from the /config section.
>
> - Felix
>
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