require short declarations when types are implicit

[mvdan]

That is, rewrite var name = value into name := value. The same would happen for var n1, n2 = v1, v2, which would become n1, n2 := v1, v2.

Exceptions:

• Globals, because name := value is only valid as a statement
• var name Type = value and var name Type

The only edge case I see is var name = zerovalue, like var s = "". Rewriting that to s := "" is fine, but some people might prefer var s string. Then again, if people prefer that form, they can use it directly and the tool won't change it.