Add more postfix completions

[fbricon]

Compare jdt.ls postfix proposals:

to IDEA's:

I'd prioritize the for* and sou* proposals

[jdneo]

The list of postfix (from IDEA):

Status	key in JDT.LS	key in IDEA	template content
		!	!expr
		arg	functionCall(expr)
		assert	assert expr
✅	cast	cast	((SomeType) expr)
		castvar	T name = (T)expr
✅	else	else	if (!expr)
		field	myField = expr
✅	for	for, iter	for (T item : expr)
✅	fori	fori	for (int i = 0; i < expr.length; i++)
✅	format	format	String.format(expr)
✅	forr	forr	for (int i = expr.length-1; i >= 0; i--)
✅	if	if	if (expr)
		instanceof, inst	expr instanceof Type ? ((Type) expr). : null")
		lambda	() -> expr
		new	new T()
✅	not	not	!expr
✅	nnull	notnull, nn	if (expr != null)
✅	null	null	if (expr == null)
		opt	Optional.ofNullable(expr)
✅	par	par	(expr)
		reqnonnull	Objects.requireNonNull(expr)
		return	return expr
✅	syserr	serr	System.err.println(expr)
✅	sysouf	souf	System.out.printf("", expr)
✅	sysout	sout	System.out.println(expr)
✅	sysoutv	soutv	System.out.println(expr)
		stream	Arrays.stream(expr)
		switch	switch(expr)
		synchronized	synchronized (expr)
✅	throw	throw	throw expr
		try	try { exp } catch(Exception e)
		twr	try(Type f = new Type()) catch (Exception e)
		val, varl	lombok.var name = expr
✅	var	var	T name = expr
✅	while	while	while (expr) {}

[rgrunber]

Clients may need to consolidate their snippets (if such support exists) the more we start offering from the server-side. For example, vscode-java provides its own switch snippet (no context), but if we did add our own switch server-side (for postfix), there would be an annoying duplicate. Clients would need to enable/disable certain snippets based on whether postfix is enabled.

We'll definitely need to review how we contribute snippets as there's advantages/disadvantages to server-side & recommending client-side.

Update: Similar discussion at https://github.com/redhat-developer/vscode-java/issues/2867 (regarding snippet consolidation) .

[baober90]

I can not use postfix in lambda. for example: there is no .var postfix for cmp

[jdneo]

@baober90 We do have some issues about the lambda support. Root cause is that the AST parser could not properly parse the AST when it comes to lambda expression.