[dev.typeparams] cmd/compile/internal/types2: must not import a package called "init"

Updates #43962.

Change-Id: I070153c55baec62d13ca9284f02781b8c1276844
Reviewed-on: https://go-review.googlesource.com/c/go/+/287494
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

src/cmd/compile/internal/types2/resolver.go

@@ -250,14 +250,6 @@ func (check *Checker) collectObjects() {
 					continue
 				}
 
-				// add package to list of explicit imports
-				// (this functionality is provided as a convenience
-				// for clients; it is not needed for type-checking)
-				if !pkgImports[imp] {
-					pkgImports[imp] = true
-					pkg.imports = append(pkg.imports, imp)
-				}
-
 				// local name overrides imported package name
 				name := imp.name
 				if s.LocalPkgName != nil {
@@ -267,10 +259,19 @@ func (check *Checker) collectObjects() {
 						check.errorf(s.LocalPkgName, `cannot rename import "C"`)
 						continue
 					}
-					if name == "init" {
+				}
-						check.errorf(s.LocalPkgName, "cannot declare init - must be func")
+
-						continue
+				if name == "init" {
-					}
+					check.errorf(s.LocalPkgName, "cannot import package as init - init must be a func")
+					continue
+				}
+
+				// add package to list of explicit imports
+				// (this functionality is provided as a convenience
+				// for clients; it is not needed for type-checking)
+				if !pkgImports[imp] {
+					pkgImports[imp] = true
+					pkg.imports = append(pkg.imports, imp)
 				}
 
 				pkgName := NewPkgName(s.Pos(), pkg, name, imp)

src/cmd/compile/internal/types2/testdata/importdecl0/importdecl0a.src

@@ -10,7 +10,7 @@ import (
 	// we can have multiple blank imports (was bug)
 	_ "math"
 	_ "net/rpc"
-	init /* ERROR "cannot declare init" */ "fmt"
+	init /* ERROR "cannot import package as init" */ "fmt"
 	// reflect defines a type "flag" which shows up in the gc export data
 	"reflect"
 	. /* ERROR "imported but not used" */ "reflect"

test/fixedbugs/issue43962.dir/a.go

@@ -0,0 +1,5 @@
+// Copyright 2021 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 init

test/fixedbugs/issue43962.dir/b.go

@@ -0,0 +1,7 @@
+// Copyright 2021 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
+
+import "./a" // ERROR "cannot import package as init"

test/fixedbugs/issue43962.go

@@ -0,0 +1,9 @@
+// errorcheckdir
+
+// Copyright 2021 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.
+
+// Issue 43962: Importing a package called "init" is an error.
+
+package ignored