Fix completions in range expressions

[DoctorKrolic]

Fixes: #66903

[CyrusNajmabadi]

Thanks!

[DoctorKrolic]

@CyrusNajmabadi Do the azp thing please. This is the third time in a row when I have roslyn-CI job stuck at "Waiting for status to be reported". It seems something is broken there

And also enable auto-merge please

[CyrusNajmabadi]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 4 pipeline(s).

[CyrusNajmabadi]

Thanks!

[DoctorKrolic]

@CyrusNajmabadi Updated test that previously checked for no completions after ... Please verify that the change is correct

[CyrusNajmabadi]

Thanks!

[DoctorKrolic]

@CyrusNajmabadi The result of not treating .. as a trigger sequence is a break in list pattern completions (completions are no longer invoked in cases like typing a dot in someCollection is [.$$] scenario). I looked through code and it seems that at that stage we don't have a syntax tree to check that, only source text and position. What should we do?

[CyrusNajmabadi]

(completions are no longer invoked in cases like typing a dot in someCollection is [.$$] scenario)

Completion should not be triggered here on dot. dot completion is for actually dotting off of some entity. There is no entity here, so i would not expect the second dot to trigger anything.

[DoctorKrolic]

Well, failed test verify opposite, e.g.:

roslyn/src/EditorFeatures/Test2/IntelliSense/CSharpCompletionCommandHandlerTests.vb

Lines 9711 to 9742 in 7347efa

	<WpfTheory, CombinatorialData>
	Public Async Function CompletionInSlicePattern_NullKeyword(showCompletionInArgumentLists As Boolean) As Task
	Using state = TestStateFactory.CreateCSharpTestState(
	<Document>
	public class RestType
	{
	}
	public class C
	{
	public int Length => 0;
	public int this[int i] => 0;
	public RestType Slice(int i, int j) => null;
	void M(C c)
	{
	_ = c is [ 0, $$ ]
	}
	}
	</Document>,
	showCompletionInArgumentLists:=showCompletionInArgumentLists, languageVersion:=LanguageVersion.Preview)
	state.SendTypeChars("..")
	Await state.AssertSelectedCompletionItem(displayText:="async", isHardSelected:=False)
	state.SendTypeChars("nu")
	Await state.AssertSelectedCompletionItem(displayText:="null", isHardSelected:=True)
	state.SendTab()
	Await state.AssertNoCompletionSession()
	Assert.Contains("c is [ 0, ..null ]", state.GetLineTextFromCaretPosition(), StringComparison.Ordinal)
	End Using
	End Function

Should I modify all such tests to invoke completion list explicitly?

[CyrusNajmabadi]

Should I modify all such tests to invoke completion list explicitly?

No. Update the test to show hte new behavior, and then have a new test that tests explicit-invoke. Thanks :)

[DoctorKrolic]

I've updated tests to verify both behaviours at the same time. We just verify that after typing the there is no completion session, then eplicitely invoke the list and verify everything else. This makes us avoid a lot of code duplication

[DoctorKrolic]

@CyrusNajmabadi PTAL

[CyrusNajmabadi]

Thanks!