E0422: A variable not every main gives

A package reads user by name, and two package mains import it — an app in cmd/web and another in cmd/admin, say. Each main has its own web.ContextProcessors(…), and the name lowers to one typed read only when every one of them gives it, with one type. Here a main lacks the processor, or gives the name with another type; the message names which. Reported by the compiler.

A main that never calls web.ContextProcessors — a command running migrations — renders no page and isn't counted.

Wrong

// cmd/web/main.go
web.ContextProcessors(web.RequestContext, auth.Context)

// cmd/admin/main.go: the same layouts, no auth.Context
web.ContextProcessors(web.RequestContext)

Right

// cmd/admin/main.go
web.ContextProcessors(web.RequestContext, auth.Context)

A package meant for mains with different lists reads what only some give explicitly, web.Var[*auth.Identity](ctx, "user"), where it knows it is there. See context processors.