https://go.dev/doc/comment#doclinks currently says:

Doc links are links of the form “[Name1]” or “[Name1.Name2]” to refer to exported identifiers in the current package

but it is somewhat ambiguous about whether the [Name1.Name2] form can refer to struct fields or only methods.

In practice, people do seem to intuitively expect references to struct fields to work; for example, this comment on types.Package.GoVersion (written by @rsc) refers to the go/ast.File.GoVersion struct field, and pkg.go.dev appears to render that reference correctly:

However, similar references within the same package are not rendered as links. For example, the reference to [CheckedFiles.SizeError] from zip.CheckedFiles.Err is currently rendered as plain text:

go/doc.Parser uses different functions to resolve intra- vs. inter-package references: it appears that the LookupPackage hook being used by pkgsite does resolve struct fields, whereas the LookupSym hook does not.