Provide diagnostics and quickfix when open non-project java file

[testforstephen]

Signed-off-by: Jinbo Wang [email protected]

Fix redhat-developer/vscode-java#1270

two kinds of non-project file:

• external Java file
• Java file not on the classpath of the active project

Improve syntax mode for the non-project Java file:

• Delete the notification message box about "classpath is incomplete. Only syntax errors will be reported".
• Add a general non-project warning diagnostic, see screenshot below.
• Provide quickfix to enable/disable semantic errors. (More quick fixes could be enabled in future, such as Add to source path for those not on classpath.)
  Enable semantic errors:
  
  Disable semantic errors:
  

[fbricon]

So if I open ./mvn/wrapper/MavenWrapperDownloader.java in a Maven project, I get no warning, no compilation error, no syntax error, no code action, even though this is technically a "Java file not on the classpath of the active project"

[testforstephen]

PR updated.

Did you sync the latest code from my branch? It works as expected in my machine.

[fbricon]

I figured out why I didn't get anything. If the Maven wrapper is under the parent project (so non-java) of other Maven Java projects, then, we end up returning no CU:

https://github.com/eclipse/eclipse.jdt.ls/blob/c026aafd84e454f77030132b7095b3971bd5a493/org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/JDTUtils.java#L175-L177

This is the case of https://github.com/eclipse/eclipse.jdt.ls/blob/master/.mvn/wrapper/MavenWrapperDownloader.java

I think this is a use case we can fix later though

[testforstephen]

PR updated.

And create a new PR #1377 to fix the no CU issue about opening file from non-java maven module.

[fbricon]

Merged as 5165dbf.
I made some changes to DiagnosticState to be able to do this:
https://github.com/eclipse/eclipse.jdt.ls/blob/5165dbf66b0c7ab1227d3be7698ba2841d690482/org.eclipse.jdt.ls.tests/src/org/eclipse/jdt/ls/core/internal/commands/DiagnosticsCommandTest.java#L62-L63