[SR-11827] Missing "in" => bad diagnostic

[dabrahams]

Previous ID	SR-11827
Radar	rdar://problem/57418525
Original Reporter	@dabrahams
Type	Bug

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: 29d9832455f9840f7ae31e4c0ca0baec

Issue Description:

  1> (0..<10).map { x
  2.     x + 1
  3. }
error: repl.swift:1:10: error: cannot invoke 'map' with an argument list of type '(@escaping () -> ())'
(0..<10).map { x
         ^

repl.swift:1:10: note: expected an argument list of type '((Self.Element) throws -> T)'
(0..<10).map { x
         ^

I've also seen, "Contextual type for closure argument list expects 1 argument, which cannot be implicitly ignored" (small reproducer harder to generate). Either way we should have an error saying "in" is missing and a fixit to insert it.

[beccadax]

@swift-ci create

[xedin]

Looks like this has been fixed recently:

(0..<10).map { x
  x + 1
}
error: cannot find 'x' in scope
(0..<10).map { x
               ^
error: cannot find 'x' in scope
  x + 1
  ^
error: contextual type for closure argument list expects 1 argument, which cannot be implicitly ignored
(0..<10).map { x
             ^
               _ in

Please verify using the most recent main branch toolchain from swift.org.

[AnthonyLatsis]

This sort of thing has come up before. I think we need a parser heuristic that would warn about argument-list-like syntax written on the same line as { when in cannot be found and the next token is on a different line. The obvious way to silence this warning would be to insert either the in keyword or a line break after {.