Completion: add support for keywords like public, class, etc.

[starbar]

To test the completion function of the server, I run the java file groovy-language-server/src/test/java/net/prominic/groovyls/GroovyServicesCompletionTests.java and successfully output the result. For example, when I let the input content be:

class Completion {
  public Completion() {
    String localVar
    localV

The position (3, 10) will return the label localVar.
However, when I let the input content be:

clas

The position (0, 4) return null，which I think it should return the label class.
And when I let the input content be:

class Completion {
  publi

The position (1, 7) also return null, which I think it should return the label public.
Such situation that the completion result is null is common. So I want to consult why these cases happen and how can I get the ideal completion results.
Looking forward for your answers, thanks!

[joshtynjala]

I don't think that completion for keywords like class and public has been implemented at this time. It's mostly names of things like variables, functions, and classes.

[starbar]

Except for the keyword like public, class, etc, some situations about the completion for local variable also return null, like the following cases.

Case 1:

\*content*\
class Completion {
  public Completion(){ 
    String localVar
        localV

\*position*\
(3, 14)  \\The position after "localV"
    
\*output label*\
localVar


\*Null Return Situation*\
\*content*\
class Completion {
    String localVar
        localV

\*position*\
(2, 14)  \\The position after "localV"
    
\*output label*\
null 

In the Case 1, deleting the code snippet public Completion(){ , which seems to have no strong association with the completion request, will cause null return.

Case 2:

\*content*\
class Completion {
  String memberVar{
  public Completion() {
    mem
  }
}

\*position*\
(3, 7)  \\The position after "mem"
    
\*output label*\
memberVar
    

\*Null Return Situation*\
\*content*\
class Completion {
  String memberVar{
  public Completion() {
    mem
  }


\*position*\
(3, 7)  \\The position after "mem"
    
\*output label*\
null

In Case 2, deleting the last { will cause null return. Whether the syntax error will affect the completion result? In fact the Case 1 also has syntax error but the expected label is still returned.

Is there any standard about the completion rules? Or there are some code snippets that I can debug to find its completion rules? Since the project is developed based on many jar packages, it is hard to locate the completion rule of the LSP server.

[joshtynjala]

Yes, syntax errors can cause completion to fail. The language server uses the Groovy compiler, which expects to receive valid syntax. The language server has a few simple workarounds for basic syntax errors, but it is not comprehensive. Your syntax needs to be mostly correct, including proper brackets for things like classes and methods.

The completion code may be found here in CompletionProvider:

https://github.com/prominic/groovy-language-server/blob/master/src/main/java/net/prominic/groovyls/providers/CompletionProvider.java

Some workarounds for bad syntax may be found here (see the GroovyServices.completion() method):

https://github.com/prominic/groovy-language-server/blob/master/src/main/java/net/prominic/groovyls/GroovyServices.java#L214