On 2007-07-10 13:04:50 +0200, Kenney Westerhof <[EMAIL PROTECTED]> said:
currently, Maven does not require declaration of properties used in the
pom, you just use them anywhere you like. Usually, if a property is
missing, bad things tend to happen because it is replaced with the
string "null". On a good day, resources from "translations-null-null"
When/where is it null?
Just an example. What I was trying to say is that if a required
property is missing, and the developer forgot to set a default, the
build will do unexpected things. Mostly happens to me though when build
paths depend on properties.
aren't included in the build, on bad days it's worse... And when you
find the missing property in a pom you haven't written, you have to
figure out what "${lopt}" means and what its legal values are...
True, but proper defaults should be specified in the pom itself using
the normal properties tag. Commandline, profiles, and settings
can override these. A pom should just work out of the box. If you
want to customize it you'll have to read the pom to see what can be customized;
there should be a readme or documentation in the pom for that.
It may not be possible to set a proper default in the pom, because the
property depends on the user's system or organization. Examples are a
deployment location or the local company repository. I think it is
better to specify that such a value is required (and tell the user
about this) than to put a default in there that the user surely cannot
work with.
I first proposed to make the declaration mandatory, so the
specification of proper defaults would be required, instead of optional
and error-prone. I forgot about plugins... So the proposal should be
downscaled to "required specification if the property is referenced in
the pom.xml in any way". This would enforce the "working out of the
box" of the pom, and people know where to look for the property
documentation. In addition, having a property specification allows for
additional nice things, e.g. "mvn -interactive", promping you for the
options.
Commandline, profiles and settings still can override these, but if the
property is fully specified, only legal values can be used, preventing
unexpected behaviour.
There's lots of cases where properties are used - pom interpolation,
plugin configuration, filtering.. which one are you talking about?
All properties referenced in the pom.xml
For pom interpolation, you may not always want properties evaluated.
In any case, if the property can't be evaluated, the ${expression} is
left intact. So the null case doesn't apply here..
For plugin configuration, you cannot possibly list all properties for all
plugins out there.
For filtering, you may just want to print a warning or fail; this could
be configured in the resources plugin.
So how/when do you get the 'translations-null-null' problem exactly?
I don't like the proposal as it's way too verbose
The minimal specification would only be
<property>
<name>xyz</name>
<value>123</value>
</property>
It's a bit more verbose than the current form, but all in all, poms are
not known for their brevity ;-)
and as others have said
only fixes a small set of problems you may have, but doesn't cover all
cases.
In my experience, this these are the problems that occur the most. Of
course, this observation is not gerneralizable. However, I think that
specifying what you use is a good principle, and property handling
seems an odd case in the "formalize-everything-you-can" pom format.
True, the plugin case cannot be handled, since you never know what a
plugin does, so this should be outside of the scope of the proposal. If
a plugin is missing a required property, it would be the job of the
plugin to complain.
As a sidetrack, maybe there is a better way to configure plugins than
properties. From a plugin developer standpoint, it seems a bit
redundant to do @parameter expression="${myproperty}" in many places
just to make a plugin parameter configurable from the command line or
settings.xml. From a user standpoint "--test:skip" would be nicer than
"-Dmaven.test.skip" (although I guess that every Maven user can type
the latter very fast :-).
There's an issue out there to make all property references/declarations
in the pom the same, preferrably <propname>value</propname>.
Perhaps a '<propertyManagement>' section is more appropriate? :)
I'll update the proposal. Thanks for the comments.
Regards,
Jochen
So instead typing
<properties>
<lopt>en_US</lopt>
</properties>
this proposal wants you to write
<properties>
<property>
<name>lopt</name>
<defaultValue>en_US</defaultValue>
<required>true</required>
<description>Locale to use</description>
<options>
<option>
<value>de_DE</value>
<description>Use German locale</description>
</option>
</options>
</property>
</properties>
This is rather verbose. Do you really want to list all locales in this case?
Of course, Maven should display an error if a required variable is
missing. And it would be nice to have "help:describe-properties"...
-- Kenney
Regards,
Jochen
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