cmd/guru: what: include imported package names in sameids

+ Test.

Change-Id: Ib7ef99786f5b60bb3e56ced9588d2ba5725576e1
Reviewed-on: https://go-review.googlesource.com/24949
Reviewed-by: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -113,6 +113,19 @@
 		}
 	]
 }
+{
+	"package": "what-json",
+	"refs": [
+		{
+			"pos": "testdata/src/what-json/main.go:13:7",
+			"text": "var _ lib.Var // @what pkg \"lib\""
+		},
+		{
+			"pos": "testdata/src/what-json/main.go:14:8",
+			"text": "type _ lib.T"
+		}
+	]
+}
 -------- @referrers ref-method --------
 {
 	"objpos": "testdata/src/lib/lib.go:5:13",

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

@@ -28,6 +28,8 @@ references to package lib
 	var v lib.Type = lib.Const // @referrers ref-package "lib"
 	var v lib.Type = lib.Const // @referrers ref-package "lib"
 	var x lib.T           // @definition lexical-pkgname "lib"
+type _ lib.T
+var _ lib.Var // @what pkg "lib"
 
 -------- @referrers ref-method --------
 references to func (Type).Method(x *int) *int

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

@@ -1,5 +1,7 @@
 package main
 
+import "lib"
+
 // Tests of 'what' queries, -format=json.
 // See go.tools/guru/guru_test.go for explanation.
 // See what-json.golden for expected query results.
@@ -7,3 +9,6 @@ package main
 func main() {
 	f() // @what call "f"
 }
+
+var _ lib.Var // @what pkg "lib"
+type _ lib.T

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

@@ -3,33 +3,33 @@
 	"enclosing": [
 		{
 			"desc": "identifier",
-			"start": 175,
+			"start": 189,
-			"end": 176
+			"end": 190
 		},
 		{
 			"desc": "function call",
-			"start": 175,
+			"start": 189,
-			"end": 178
+			"end": 192
 		},
 		{
 			"desc": "expression statement",
-			"start": 175,
+			"start": 189,
-			"end": 178
+			"end": 192
 		},
 		{
 			"desc": "block",
-			"start": 172,
+			"start": 186,
-			"end": 198
+			"end": 212
 		},
 		{
 			"desc": "function declaration",
-			"start": 160,
+			"start": 174,
-			"end": 198
+			"end": 212
 		},
 		{
 			"desc": "source file",
 			"start": 0,
-			"end": 198
+			"end": 259
 		}
 	],
 	"modes": [
@@ -46,3 +46,48 @@
 	"srcdir": "testdata/src",
 	"importpath": "what-json"
 }
+-------- @what pkg --------
+{
+	"enclosing": [
+		{
+			"desc": "identifier",
+			"start": 220,
+			"end": 223
+		},
+		{
+			"desc": "selector",
+			"start": 220,
+			"end": 227
+		},
+		{
+			"desc": "value specification",
+			"start": 218,
+			"end": 227
+		},
+		{
+			"desc": "variable declaration",
+			"start": 214,
+			"end": 227
+		},
+		{
+			"desc": "source file",
+			"start": 0,
+			"end": 259
+		}
+	],
+	"modes": [
+		"definition",
+		"describe",
+		"freevars",
+		"implements",
+		"pointsto",
+		"referrers"
+	],
+	"srcdir": "testdata/src",
+	"importpath": "what-json",
+	"object": "lib",
+	"sameids": [
+		"$GOPATH/src/what-json/main.go:13:7",
+		"$GOPATH/src/what-json/main.go:14:8"
+	]
+}

cmd/guru/what.go

@@ -117,7 +117,26 @@ func what(q *Query) error {
 	// it uses the best-effort name resolution done by go/parser.
 	var sameids []token.Pos
 	var object string
-	if id, ok := qpos.path[0].(*ast.Ident); ok && id.Obj != nil {
+	if id, ok := qpos.path[0].(*ast.Ident); ok {
+		if id.Obj == nil {
+			// An unresolved identifier is potentially a package name.
+			// Resolve them with a simple importer (adds ~100µs).
+			importer := func(imports map[string]*ast.Object, path string) (*ast.Object, error) {
+				pkg, ok := imports[path]
+				if !ok {
+					pkg = &ast.Object{
+						Kind: ast.Pkg,
+						Name: filepath.Base(path), // a guess
+					}
+					imports[path] = pkg
+				}
+				return pkg, nil
+			}
+			f := qpos.path[len(qpos.path)-1].(*ast.File)
+			ast.NewPackage(qpos.fset, map[string]*ast.File{"": f}, importer, nil)
+		}
+
+		if id.Obj != nil {
 			object = id.Obj.Name
 			decl := qpos.path[len(qpos.path)-1]
 			ast.Inspect(decl, func(n ast.Node) bool {
@@ -127,6 +146,7 @@ func what(q *Query) error {
 				return true
 			})
 		}
+	}
 
 	q.Output(qpos.fset, &whatResult{
 		path:       qpos.path,