FileRestorer Package Alias does not work for std library packages

[thesilentg]

I'm trying to use dst with import management, but this doesn't appear to work correctly when aliases are necessary for packages in the standard library. This can be necessary in the case where existing identifiers are already using the default name for a package. Example below:

Example input

package scope

import "fmt"

func myfunc2() {
    context := 5
    fmt.Println(context)
}

Desired output

package scope

import (
    "fmt"
    context1 "context"
)

func myfunc2() {
    context := 5
    fmt.Println(context)
    client{}.DoWithContext(context1.TODO())
}

The exact example shown is a bit contrived, but the core situation can be generalized. Here, the existing context variable means that trying to import the context package without an alias will fail. To get around this, I'm doing this to create an identifier with a non-standard path for the context package import.

	ident := dst.NewIdent("TODO")
	ident.Path = "context1"
	return &dst.CallExpr{
		Fun: ident,
	}

and then using a gopackages FileRestorer like this to map this non-standard path back in the import block.

	pkgs, err := decorator.Load(cfg, packagesToCheck...)
        ...
        restorer := decorator.NewRestorerWithImports(fullPath, gopackages.New(fullPath))
        ...
        fr := restorer.FileRestorer()
	fr.Alias = map[string]string{"context": "context1"}
        ...
        // Eventually
        fr.Fprint(outputBuffer, astNode.(*dst.File))

This should hopefully allow dst to manage the import block. However, it actually returns the following error: package context1 is not in std.

[thesilentg]

I realize after further testing that choosing the un-aliased path + the aliased filerestorer does work. eg:

	ident := dst.NewIdent("TODO")
	ident.Path = "context"
	return &dst.CallExpr{
		Fun: ident,
	}

fr := restorer.FileRestorer()
fr.Alias = map[string]string{"context": "context1"}

The documentation for Path is a bit unclear, in terms of that being the package path ("context") or the aliased path within the scope of a given file ("context1"). I'll leave this issue open in the meantime, but would you be open to any documentation updates to better clarify this for the future? If so, I'm happy to make them.