From 6394eb378eb6b2c0e691c519b2a6664f930b427e Mon Sep 17 00:00:00 2001
From: Robert Griesemer <gri@golang.org>
Date: Tue, 23 Aug 2016 16:02:19 -0700
Subject: [PATCH] cmd/compile: export package for _ (blank) struct fields

Blank struct fields are regular unexported fields. Two
blank fields are different if they are from different
packages. In order to correctly differentiate them, the
compiler needs the package information. Add it to the
export data.

Fixes #15514.

Change-Id: I421aaca22b542fcd0d66b2d2db777249cad78df6
Reviewed-on: https://go-review.googlesource.com/27639
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
---
 src/cmd/compile/internal/gc/bexport.go |  7 ++-----
 src/cmd/compile/internal/gc/bimport.go |  7 +------
 src/go/internal/gcimporter/bimport.go  | 10 +++-------
 test/fixedbugs/issue15514.dir/a.go     |  7 +++++++
 test/fixedbugs/issue15514.dir/b.go     |  7 +++++++
 test/fixedbugs/issue15514.dir/c.go     | 10 ++++++++++
 test/fixedbugs/issue15514.go           |  7 +++++++
 7 files changed, 37 insertions(+), 18 deletions(-)
 create mode 100644 test/fixedbugs/issue15514.dir/a.go
 create mode 100644 test/fixedbugs/issue15514.dir/b.go
 create mode 100644 test/fixedbugs/issue15514.dir/c.go
 create mode 100644 test/fixedbugs/issue15514.go

diff --git a/src/cmd/compile/internal/gc/bexport.go b/src/cmd/compile/internal/gc/bexport.go
index 9c1ccd87a1..a43158d14b 100644
--- a/src/cmd/compile/internal/gc/bexport.go
+++ b/src/cmd/compile/internal/gc/bexport.go
@@ -858,11 +858,9 @@ func (p *exporter) method(m *Field) {
 	p.paramList(m.Type.Results(), false)
 }
 
-// fieldName is like qualifiedName but it doesn't record the package
-// for blank (_) or exported names.
+// fieldName is like qualifiedName but it doesn't record the package for exported names.
 func (p *exporter) fieldName(t *Field) {
 	name := t.Sym.Name
-
 	if t.Embedded != 0 {
 		name = "" // anonymous field
 		if bname := basetypeName(t.Type); bname != "" && !exportname(bname) {
@@ -871,8 +869,7 @@ func (p *exporter) fieldName(t *Field) {
 		}
 	}
 	p.string(name)
-
-	if name != "_" && name != "" && !exportname(name) {
+	if name != "" && !exportname(name) {
 		p.pkg(t.Sym.Pkg)
 	}
 }
diff --git a/src/cmd/compile/internal/gc/bimport.go b/src/cmd/compile/internal/gc/bimport.go
index 0e30031f07..65c845c93a 100644
--- a/src/cmd/compile/internal/gc/bimport.go
+++ b/src/cmd/compile/internal/gc/bimport.go
@@ -590,12 +590,7 @@ func (p *importer) method() *Node {
 func (p *importer) fieldName() *Sym {
 	name := p.string()
 	pkg := localpkg
-	if name == "_" {
-		// During imports, unqualified non-exported identifiers are from builtinpkg
-		// (see parser.go:sym). The binary exporter only exports blank as a non-exported
-		// identifier without qualification.
-		pkg = builtinpkg
-	} else if name != "" && !exportname(name) {
+	if name != "" && !exportname(name) {
 		if name == "?" {
 			name = ""
 		}
diff --git a/src/go/internal/gcimporter/bimport.go b/src/go/internal/gcimporter/bimport.go
index 87701f99de..b657cc79ba 100644
--- a/src/go/internal/gcimporter/bimport.go
+++ b/src/go/internal/gcimporter/bimport.go
@@ -492,19 +492,15 @@ func (p *importer) method(parent *types.Package) *types.Func {
 }
 
 func (p *importer) fieldName(parent *types.Package) (*types.Package, string) {
+	name := p.string()
 	pkg := parent
 	if pkg == nil {
 		// use the imported package instead
 		pkg = p.pkgList[0]
 	}
-	name := p.string()
-	if name == "" {
-		return pkg, "" // anonymous
-	}
-	if name == "?" || name != "_" && !exported(name) {
-		// explicitly qualified field
+	if name != "" && !exported(name) {
 		if name == "?" {
-			name = "" // anonymous
+			name = ""
 		}
 		pkg = p.pkg()
 	}
diff --git a/test/fixedbugs/issue15514.dir/a.go b/test/fixedbugs/issue15514.dir/a.go
new file mode 100644
index 0000000000..663303b863
--- /dev/null
+++ b/test/fixedbugs/issue15514.dir/a.go
@@ -0,0 +1,7 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package a
+
+type A struct{ _ int32 }
diff --git a/test/fixedbugs/issue15514.dir/b.go b/test/fixedbugs/issue15514.dir/b.go
new file mode 100644
index 0000000000..f0750d3a44
--- /dev/null
+++ b/test/fixedbugs/issue15514.dir/b.go
@@ -0,0 +1,7 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package b
+
+func B() (_ struct{ _ int32 }) { return }
diff --git a/test/fixedbugs/issue15514.dir/c.go b/test/fixedbugs/issue15514.dir/c.go
new file mode 100644
index 0000000000..11624f9256
--- /dev/null
+++ b/test/fixedbugs/issue15514.dir/c.go
@@ -0,0 +1,10 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package c
+
+import "./a"
+import "./b"
+
+var _ a.A = b.B() // ERROR "cannot use b\.B"
diff --git a/test/fixedbugs/issue15514.go b/test/fixedbugs/issue15514.go
new file mode 100644
index 0000000000..626f7ad699
--- /dev/null
+++ b/test/fixedbugs/issue15514.go
@@ -0,0 +1,7 @@
+// errorcheckdir
+
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ignored
-- 
2.48.1