Re: [tycho-dev] [pde-dev] Resolving against multiple .target files

[Curtis Windatt <Curtis_Windatt@xxxxxxxxxx>]

HI Mickael,

I'm sure there are use cases where users
want to extend existing targets.  I'm not as certain that users need
to be able to merge two target definitions.  Right now a user can
duplicate an existing target file and add to it.  My concern is that
your suggestion of multi-select on the preference page will add confusion
to the more common workflows.

For reference, the page has checkboxes
because we wanted to use a Table widget, not because we intended for it
to be mult-select.  Any change here should consider what workflow/UI
changes would be necessary if someday we support multiple target platforms
in the workspace (target per project).

From a code perspective.  This
change would require changes to the target API.  Depending on how
it is implemented, it changes a significant assumption "there is one
target platform defined by one ITargetDefinition".  Loading bundles
from two targets isn't difficult.  However, what about other conflicting
information such as OS/Arch/JRE/Implicit bundles.  I'm not sure about
performance costs.  The resolution time would double, but the p2 caching
scheme might not work correctly.  I could also see some flakiness
due to how we store the target bundles in preferences for legacy reasons.

In conlusion, PDE doesn't support this
change as described.  If there is another workflow that would satisfy
your use cases we can take another look (i.e. Allowing target definitions
to import from other target definitions dynamically).

Curtis

From:	Mickael Istria <mistria@xxxxxxxxxx>
To:	pde-dev@xxxxxxxxxxx,
Cc:	Tycho developers list <tycho-dev@xxxxxxxxxxx>
Date:	2012/09/07 09:13 AM
Subject:	[pde-dev] Resolving against multiple .target files
Sent by:	pde-dev-bounces@xxxxxxxxxxx

---

Hi all,

I'm cross-posting this discussion to both pde-dev and tycho-dev lists,
please ensure you are subscribed to both and use "Reply To All".

This discussion is intended to have opinion from PDE folks on this enhancement
request: https://github.com/mickaelistria/tycho/tree/388909
"Allow multiple target files as input of target-platform-configuration
plugin".

The general idea is that, in big "composite" projects, we may
have most of the target-platforms (TP) in common between all components,
and each component may want to provide an extension to this target-platform.
It is the case for JBoss Tools, for which we'd like to provide all external/core
-Eclipse, Atlassian, GWT...- dependencies in a target-platform that components
would be forced to use, in order to ensure all components work together
on the dependencies specified by the TP. Then each component should be
able to "extend" this target-platform to add its internal dependencies
on other JBoss components.
However, TPs are published to Nexus for sharing, and we don't want components
to take and tweak our core TP.

In Tycho, that could be achieved by allowing support of several TPs simultaneously.
So component B would say to Tycho: I want to resolve against the Core TP
+ this TP of mine (which defines dependencies on component A). Tycho would
then resolve against those 2 TPs, just as if their locations were merged
in a single .target file.
It's all about supporting some "pieces of target-platform".

What is the opinion of PDE guys on this topic? I think, given JBoss Tools
use-cases that this is something that makes also a lot of sense to support
in PDE, and in Tycho.
Moreover, in the preference page for target platforms, there are checkboxes
instead of radio buttons, which means that I'm not the first one to think
it would be useful to select several TPs ;)

Cheers,
-- 
Mickael Istria
Eclipse developer at JBoss,
by Red Hat
My
blog - My
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