[BUG]: Improper handling of diagnostics causing unexpected behavior in formatting and autocomplete APIs

[aayushbarmecha]

Expected behavior
An incorrect PQ should highlight diagnostics

Actual behavior
Diagnostics not highlighted as expected even for incorrect PQ which results in no formatting and incorrect suggestions creating unlikely user experience along with hampered API results for AutoComplete and Code Formatting

To Reproduce

• The Power Query script that triggers the issue:

1. The below code has Lex Error at second last line due to missing brackets thus breaking the overall syntax

let
	Source = Sql.Database(".", "SimpleMovies", [Query="SELECT [dbo].[Persons].* #(tab)#(tab)FROM [dbo].[Persons]"]),
	#"Renamed Columns" = Table.RenameColumns(Source, {{"Id", "Id"}, {"Height", "Height"}, {"BirthDate", "BirthDate"}, {"Nationality", "Nationality"}}),
	#"Changed Type" = Table.RenameColumns(#"Renamed Columns", {{"Id", Int64.Type}, {"FullName", type text}, {"BirthLocation", type text}, {"Country", type text}, {"ImageUrl)
in

• Any non-default settings used in the API call(s) which trigger the issue:

1. None

Additional context
Upon further investigation, the API internally seems to identify that there is a Lex Error but does not handle it in the 'validate' API.

[mattmasson]

The repro expression is missing a " in {"ImageUrl).

It looks like the current validation logic isn't reporting diagnostics when there is an unterminated string.

Diagnostics behave as expected when there is a missing brace/bracket.

[{
	"resource": "Untitled-1",
	"owner": "_generated_diagnostic_collection_name_#1",
	"code": "Error.Parse",
	"severity": 8,
	"message": "Expected to find either a comma <','> or right brace <'}'>.",
	"source": "powerquery",
	"startLineNumber": 4,
	"startColumn": 171,
	"endLineNumber": 4,
	"endColumn": 172,
	"modelVersionId": 13,
	"origin": "extHost1"
}]