Download sources for the masses

[rgrunber]

• Fixes support download of sources for classes in jar with maven coordinates redhat-developer/vscode-java#1664
• Download maven-central artifact's sources on-demand

Signed-off-by: Fred Bricon fbricon@gmail.com
[rgrunber@redhat.com]: Fix testDynamicSourceLookups()

• Move testcase from HoverHandlerTest to InvisibleProjectBuildSupportTest
• Set up the external library after project import to mimic approach
  in other invisible projects
  Signed-off-by: Roland Grunberg rgrunber@redhat.com

@fbricon

Based on #1580 .

[testforstephen]

Tried it in an unmanaged folder (invisible project), the downloader works.

Need a PR in the client side to expose the new preference key. Others look good to me.

[fbricon]

IIRC there's one case that doesn't work well: Take an invisible project with 2 jars in lib/ , if you hover over a class from jar 1, source is downloaded, classpath is updated with path to sources of jar 1, if you hover over a class from jar 2, source is downloaded, classpath is updated with path to sources of jar 2, but sourcepath of jar 1 is lost

[rgrunber]

IIRC there's one case that doesn't work well: Take an invisible project with 2 jars in lib/ , if you hover over a class from jar 1, source is downloaded, classpath is updated with path to sources of jar 1, if you hover over a class from jar 2, source is downloaded, classpath is updated with path to sources of jar 2, but sourcepath of jar 1 is lost

I could have a look and see what would be involved in fixing. I'd lean towards filing a separate bug for this as it would be good to get some initial support in for mid-January.

UPDATE : @fbricon I tried a simple invisible project with 2 jars from maven central in lib/ and a source file with references to types from those jars. Whether I hovered/go-to defition on one and then the other while watching the hidden .classpath file and the classpath 'lib' entries were updated with a sourcepath to the local repository location and it never went away.

[testforstephen]

UPDATE : @fbricon I tried a simple invisible project with 2 jars from maven central in lib/ and a source file with references to types from those jars. Whether I hovered/go-to defition on one and then the other while watching the hidden .classpath file and the classpath 'lib' entries were updated with a sourcepath to the local repository location and it never went away.

I also tried an invisible project with 2 jars, and the source path metadata didn't disappear while hovering over the class from another jar.

[rgrunber]

As redhat-developer/vscode-java#1758 is ready for submission and this change is also now in good shape, I'll be pushing these in by the end of today.

[rgrunber]

Ok, so @fbricon clarified a possible reproducer and seems specific to invisible projects.

1. Set up the invisible project (include a jar in the lib/ folder)
2. Update the project classpath by adding a second jar to the lib folder

The first jar's source classpath should disappear likely due to a bug with the invisible project's classpath updating logic.

I haven't tested this out, but if so, I can file a bug for this.