constlit

Constlit is an analysis package that identifies literal expressions that should be replaced by local or imported constants.

Before

import "image/png"

var enc := png.Encoder{CompressionLevel: -2}

import "image/png"

var enc := png.Encoder{CompressionLevel: png.BestSpeed}

Constlit uses some arbitrary heuristics to avoid making horrible recommendations.

Only recommend constants from the local package, or from packages it already imports
Only recommend constants from imported packages that are of a defined type (not untyped, or plain int, etc.)
Don't recommend constants to replace multiplied literals (i.e. 1 * time.Minute)