Maybe the go generate is generating the imports,
or maybe there's some other good reason the code
is incomplete.

The help text already says:

	Note that go generate does not parse the file, so lines that look
	like directives in comments or multiline strings will be treated
	as directives.

We'll still reject Go source files that don't begin with a package statement
or have a syntax error in the import block, but those are I think more
defensible rejections.

Fixes #16307.

Change-Id: I4f8496c02fdff993f038adfed2df4db7f067dc06
Reviewed-on: https://go-review.googlesource.com/31659
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>