Improve package version constraint suggestions.

Improve package version constraint suggestions.

Prerelease versions now suggest the stable version as the upper bound,
which provides a compromise between flexibility and potential breakage.
Other versions now use the caret syntax, since most active versions of
pub support it at this point.

Closes #266
See #274

R=kustermann@google.com

Committed: https://github.com/dart-lang/pub-dartlang/commit/a43ed13ab14004387e9f1ca960b2e91f15de52ce

[nweiz, 2015-05-18 20:08:15]

nweiz@google.com changed reviewers:
+ kustermann@google.com

[kustermann, 2015-05-19 08:24:36]

https://chromiumcodereview.appspot.com/1140493005/diff/1/app/models/package_v...
File app/models/package_version.py (right):

https://chromiumcodereview.appspot.com/1140493005/diff/1/app/models/package_v...
app/models/package_version.py:255: ))
I'm not sure if this is working as intended.

A while ago I filed http://dartbug.com/20404 which was marked as AsDesigned and
says basically:
  "0.0.3-dev" does not satisfy the constraint '>=0.0.3-dev <0.0.3'

=> Your change builds exactly such a constraint.


Now since pub defines it's *own semantics* of what constraints and the operators
<, <=, >, >= mean, and I'm not a pub expert, I don't know what to use. This
issue http://dartbug.com/20302 says:

  "<1.2.3"   No pre-release versions are considered
  "<=1.2.3"  Pre-release versions are considered

This might indicate that we could do:
 a)  ">=1.2.3-dev <=1.2.3"
 b)  ">=1.2.3-dev <=1.2.3-dev"

If option a) is not desired, because we don't want to include 1.2.3, then option
b) seems to be the only choice.


But you're much more familiar with pub's semantic versioning, so maybe I'm
misunderstanding something here?

[nweiz, 2015-05-19 18:40:35]

On 2015/05/19 08:24:36, kustermann wrote:
>
https://chromiumcodereview.appspot.com/1140493005/diff/1/app/models/package_v...
> File app/models/package_version.py (right):
> 
>
https://chromiumcodereview.appspot.com/1140493005/diff/1/app/models/package_v...
> app/models/package_version.py:255: ))
> I'm not sure if this is working as intended.
> 
> A while ago I filed http://dartbug.com/20404 which was marked as AsDesigned
and
> says basically:
>   "0.0.3-dev" does not satisfy the constraint '>=0.0.3-dev <0.0.3'
> 
> => Your change builds exactly such a constraint.
> 
> 
> Now since pub defines it's *own semantics* of what constraints and the
operators
> <, <=, >, >= mean, and I'm not a pub expert, I don't know what to use. This
> issue http://dartbug.com/20302 says:
> 
>   "<1.2.3"   No pre-release versions are considered
>   "<=1.2.3"  Pre-release versions are considered
> 
> This might indicate that we could do:
>  a)  ">=1.2.3-dev <=1.2.3"
>  b)  ">=1.2.3-dev <=1.2.3-dev"
> 
> If option a) is not desired, because we don't want to include 1.2.3, then
option
> b) seems to be the only choice.
> 
> 
> But you're much more familiar with pub's semantic versioning, so maybe I'm
> misunderstanding something here?

That's a good point. It looks like pub doesn't actually match npm's semantics
here; npm would allow this constraint. I'll fix pub_semver to match npm, but
until that's been out for a few versions we probably shouldn't advertise it on
the site.

I've updated both CLs to remove the special case for prerelease versions.

[kustermann, 2015-05-19 20:06:15]

LGTM - Although personally I find upper+lower bound to be more self-describing
for (in particular) new users than the '^' notation. But it makes for sure sense
for people how know what it implies.

[nweiz, 2015-05-19 20:47:01]

Committed patchset #2 (id:20001) manually as
a43ed13ab14004387e9f1ca960b2e91f15de52ce (presubmit successful).