Support allowlisting via a comment rather than global config

[ImprintNav]

Having to specify every covered struct in a global configuration file isn't ideal for reasons such as build incrementalism. I suggest also supporting an approach similar to the one used in nishanths/exhaustive, except at the struct level.

//exhaustruct:enforce
type Params struct {
    RequiredInt       int
    RequiredString string
}

type Data struct {
    OptionalInt       int
    OptionalString string
}

Unlike in that other analyzer, it probably makes sense to always enforce presence at every site of struct initialization by default if the struct is configured to require parameters. This is consistent with e.g. how most languages deal with named, required parameters to function calls.

A global configuration flag -explicit-exhaustive-struct with default value false would be required to maintain backwards compatibility (in the sense of ensuring previously failed builds continue to fail).

[navijation]

@xobotyi Do you have any thoughts on the merits of this suggestion? It is likely to cause a performance hit due to multi-pass, but that can be gated by a flag. The added cost is likely worth it for many organizations compared to the cache invalidation cost of editing the golangci-lint config upon every new struct to be allowlisted.

[xobotyi]

It is somehow achievable without true multipass - i've been planning to review this\next week when ill have some free time.