go.oracle: freevars: don't report free identifiers defined in package scope.

The existing check rejected only free identifiers defined in
file scope, i.e. just imports.

+ regression test.

R=crawshaw, gri
CC=golang-dev
https://golang.org/cl/13256050

oracle/freevars.go

@@ -28,6 +28,8 @@ import (
 //
 func freevars(o *oracle) (queryResult, error) {
 	file := o.queryPath[len(o.queryPath)-1] // the enclosing file
+	fileScope := o.queryPkgInfo.Scopes[file]
+	pkgScope := fileScope.Parent()
 
 	// The id and sel functions return non-nil if they denote an
 	// object o or selection o.x.y that is referenced by the
@@ -61,11 +63,12 @@ func freevars(o *oracle) (queryResult, error) {
 		if !(file.Pos() <= obj.Pos() && obj.Pos() <= file.End()) {
 			return nil // not defined in this file
 		}
-		if obj.Parent() == nil {
-			return nil // e.g. interface method  TODO(adonovan): what else?
+		scope := obj.Parent()
+		if scope == nil {
+			return nil // e.g. interface method, struct field
 		}
-		if obj.Parent() == o.queryPkgInfo.Scopes[file] {
-			return nil // defined at file scope
+		if scope == fileScope || scope == pkgScope {
+			return nil // defined at file or package scope
 		}
 		if o.startPos <= obj.Pos() && obj.Pos() <= o.endPos {
 			return nil // defined within selection => not free

oracle/testdata/src/main/freevars.go

@@ -15,6 +15,8 @@ type S struct {
 	t T
 }
 
+func f(int) {}
+
 func main() {
 	type C int
 	x := 1
@@ -29,6 +31,8 @@ func main() {
 		println(s.x + s.t.a + s.t.b + x + int(y)) // @freevars fv2 "print.*y."
 	}
 
+	f(x) // @freevars fv3 "f.x."
+
 	// TODO(adonovan): enable when go/types supports labels.
 loop: // #@freevars fv-def-label "loop:"
 	for {

oracle/testdata/src/main/freevars.golden

@@ -12,3 +12,7 @@ var s.x int
 var x int
 var y int32
 
+-------- @freevars fv3 --------
+Free identifers:
+var x int
+