cmd/guru: show correct definition for embedded type.

Fixes golang/go#16263.

Change-Id: I081a12306ac5415d2223e3509a29a1b47700e1ff
Reviewed-on: https://go-review.googlesource.com/27001
Reviewed-by: Alan Donovan <adonovan@google.com>

cmd/guru/definition.go

@@ -86,12 +86,19 @@ func definition(q *Query) error {
 		return fmt.Errorf("no identifier here")
 	}
 
-	obj := qpos.info.ObjectOf(id)
+	// Look up the declaration of this identifier.
+	// If id is an anonymous field declaration,
+	// it is both a use of a type and a def of a field;
+	// prefer the use in that case.
+	obj := qpos.info.Uses[id]
 	if obj == nil {
-		// Happens for y in "switch y := x.(type)",
-		// and the package declaration,
-		// but I think that's all.
-		return fmt.Errorf("no object for identifier")
+		obj = qpos.info.Defs[id]
+		if obj == nil {
+			// Happens for y in "switch y := x.(type)",
+			// and the package declaration,
+			// but I think that's all.
+			return fmt.Errorf("no object for identifier")
+		}
 	}
 
 	if !obj.Pos().IsValid() {

cmd/guru/testdata/src/definition-json/main.go

@@ -1,8 +1,8 @@
 package definition
 
 // Tests of 'definition' query, -json output.
-// See go.tools/guru/guru_test.go for explanation.
-// See definition.golden for expected query results.
+// See golang.org/x/tools/cmd/guru/guru_test.go for explanation.
+// See main.golden for expected query results.
 
 // TODO(adonovan): test: selection of member of same package defined in another file.
 
@@ -42,3 +42,27 @@ type T struct{ field int }
 func (T) method()
 
 type U struct{ T }
+
+type V1 struct {
+	W // @definition embedded-other-file "W"
+}
+
+type V2 struct {
+	*W // @definition embedded-other-file-pointer "W"
+}
+
+type V3 struct {
+	int // @definition embedded-basic "int"
+}
+
+type V4 struct {
+	*int // @definition embedded-basic-pointer "int"
+}
+
+type V5 struct {
+	lib.Type // @definition embedded-other-pkg "Type"
+}
+
+type V6 struct {
+	T // @definition embedded-same-file "T"
+}

cmd/guru/testdata/src/definition-json/main.golden

@@ -65,3 +65,29 @@ Error: no object for identifier
 	"objpos": "testdata/src/definition-json/main.go:42:10",
 	"desc": "func (T).method()"
 }
+-------- @definition embedded-other-file --------
+{
+	"objpos": "testdata/src/definition-json/type.go:3:6",
+	"desc": "type W int"
+}
+-------- @definition embedded-other-file-pointer --------
+{
+	"objpos": "testdata/src/definition-json/type.go:3:6",
+	"desc": "type W int"
+}
+-------- @definition embedded-basic --------
+
+Error: int is built in
+-------- @definition embedded-basic-pointer --------
+
+Error: int is built in
+-------- @definition embedded-other-pkg --------
+{
+	"objpos": "testdata/src/lib/lib.go:3:6",
+	"desc": "type lib.Type"
+}
+-------- @definition embedded-same-file --------
+{
+	"objpos": "$GOPATH/src/definition-json/main.go:40:6",
+	"desc": "type T"
+}

cmd/guru/testdata/src/definition-json/type.go

@@ -0,0 +1,3 @@
+package definition
+
+type W int

cmd/guru/testdata/src/referrers-json/main.golden

@@ -32,6 +32,10 @@
 		{
 			"pos": "testdata/src/definition-json/main.go:30:8",
 			"text": "\tvar _ lib.Nonesuch // @definition qualified-nomember \"Nonesuch\""
+		},
+		{
+			"pos": "testdata/src/definition-json/main.go:63:2",
+			"text": "\tlib.Type // @definition embedded-other-pkg \"Type\""
 		}
 	]
 }

cmd/guru/testdata/src/referrers/main.golden

@@ -13,6 +13,7 @@ references to package lib
 	_ = (lib.Type).Method // ref from internal test package
 	const c = lib.Const // @describe ref-const "Const"
 	lib.Func()          // @describe ref-func "Func"
+	lib.Type // @definition embedded-other-pkg "Type"
 	lib.Var++           // @describe ref-var "Var"
 	var _ lib.Const    // @definition qualified-const "Const"
 	var _ lib.Func     // @definition qualified-func "Func"