Completion for `in` keyword #4045

Job	Run time
Coverage (4.14.x)	4m 49s
Build and Test (macos-latest, 4.14.x)	23m 48s
Build and Test (ubuntu-latest, 4.14.x)	5m 27s
Build and Test (ubuntu-latest, 5.0.x)	3m 35s
Build and Test (ubuntu-latest, 5.1.x)	7m 3s
Build and Test (windows-latest, 4.14.x)	12m 31s
	57m 13s

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