proc: allow "package/path".varname syntax

If the application being debugged imports two packages with the same
name (but different paths) there was no way to disambiguate the two,
since the character '/' can not appear inside a go identifier.

By allowing users to use a string literal as the package name a package
path can be specified.

Documentation/cli/expr.md

@@ -81,3 +81,12 @@ To use a field of a struct contained inside an interface variable use a type ass
 (dlv) p iface1.(*main.astruct).B
 2
 ```
+
+# Specifying package paths
+
+Packages with the same name can be disambiguated by using the full package path. For example, if the application imports two packages, `some/package` and `some/other/package`, both defining a variable `A`, the two variables can be accessed using this syntax:
+
+```
+(dlv) p "some/package".A
+(dlv) p "some/other/package".A
+```

_fixtures/pkgrenames.go

@@ -51,5 +51,5 @@ func main() {
 	m := t.Method(0)
 	fmt.Println(m.Type.In(0))
 	fmt.Println(m.Type.String())
-	fmt.Println(badexpr, req, amap, amap2, dir0someType, dir1someType, amap3, anarray, achan, aslice, afunc, astruct, astruct2, iface2iface, iface3, pkg.SomeVar)
+	fmt.Println(badexpr, req, amap, amap2, dir0someType, dir1someType, amap3, anarray, achan, aslice, afunc, astruct, astruct2, iface2iface, iface3, pkg.SomeVar, pkg.A, dir1pkg.A)
 }

_fixtures/vendor/dir0/pkg/main.go

 package pkg
 
+var A = 0
+
 type SomeType struct {
 	X float64
 }

_fixtures/vendor/dir1/pkg/main.go

 package pkg
 
+var A = 1
+
 type SomeType struct {
 	X int
 	Y int

pkg/proc/eval.go

@@ -11,6 +11,7 @@ import (
 	"go/printer"
 	"go/token"
 	"reflect"
+	"strconv"
 
 	"github.com/derekparker/delve/pkg/dwarf/godwarf"
 	"github.com/derekparker/delve/pkg/dwarf/reader"
@@ -187,6 +188,15 @@ func (scope *EvalScope) evalAST(t ast.Expr) (*Variable, error) {
 				return v, nil
 			}
 		}
+		// try to accept "package/path".varname syntax for package variables
+		if maybePkg, ok := node.X.(*ast.BasicLit); ok && maybePkg.Kind == token.STRING {
+			pkgpath, err := strconv.Unquote(maybePkg.Value)
+			if err == nil {
+				if v, err := scope.findGlobal(pkgpath + "." + node.Sel.Name); err == nil {
+					return v, nil
+				}
+			}
+		}
 		// if it's not a package variable then it must be a struct member access
 		return scope.evalStructSelector(node)
 

service/test/variables_test.go

@@ -920,6 +920,9 @@ func TestPackageRenames(t *testing.T) {
 		{"astruct", true, `interface {}(*struct { A github.com/derekparker/delve/_fixtures/vendor/dir1/pkg.SomeType; B github.com/derekparker/delve/_fixtures/vendor/dir0/pkg.SomeType }) *{A: github.com/derekparker/delve/_fixtures/vendor/dir1/pkg.SomeType {X: 1, Y: 2}, B: github.com/derekparker/delve/_fixtures/vendor/dir0/pkg.SomeType {X: 3}}`, "", "interface {}", nil},
 		{"astruct2", true, `interface {}(*struct { github.com/derekparker/delve/_fixtures/vendor/dir1/pkg.SomeType; X int }) *{SomeType: github.com/derekparker/delve/_fixtures/vendor/dir1/pkg.SomeType {X: 1, Y: 2}, X: 10}`, "", "interface {}", nil},
 		{"iface2iface", true, `interface {}(*interface { AMethod(int) int; AnotherMethod(int) int }) **github.com/derekparker/delve/_fixtures/vendor/dir0/pkg.SomeType {X: 4}`, "", "interface {}", nil},
+
+		{`"dir0/pkg".A`, false, "0", "", "int", nil},
+		{`"dir1/pkg".A`, false, "1", "", "int", nil},
 	}
 
 	ver, _ := goversion.Parse(runtime.Version())