go.tools/go.types: check for redeclarations across package files

Fixes golang/go#5506.

R=adonovan
CC=golang-dev
https://golang.org/cl/9600044

go/types/resolve.go

@@ -73,7 +73,8 @@ func (check *checker) resolve(importer Importer) (methods []*ast.FuncDecl) {
 		check.register(file.Name, pkg)
 
 		// insert top-level file objects in package scope
-		// (the parser took care of declaration errors)
+		// (the parser took care of declaration errors in a single file,
+		// but not across multiple files - hence we need to check again)
 		for _, decl := range file.Decls {
 			switch d := decl.(type) {
 			case *ast.BadDecl:
@@ -91,13 +92,13 @@ func (check *checker) resolve(importer Importer) (methods []*ast.FuncDecl) {
 							if name.Name == "_" {
 								continue
 							}
-							pkg.scope.Insert(check.lookup(name))
+							check.declareObj(pkg.scope, nil, check.lookup(name), token.NoPos)
 						}
 					case *ast.TypeSpec:
 						if s.Name.Name == "_" {
 							continue
 						}
-						pkg.scope.Insert(check.lookup(s.Name))
+						check.declareObj(pkg.scope, nil, check.lookup(s.Name), token.NoPos)
 					default:
 						check.invalidAST(s.Pos(), "unknown ast.Spec node %T", s)
 					}
@@ -111,7 +112,7 @@ func (check *checker) resolve(importer Importer) (methods []*ast.FuncDecl) {
 				if d.Name.Name == "_" || d.Name.Name == "init" {
 					continue // blank (_) and init functions are inaccessible
 				}
-				pkg.scope.Insert(check.lookup(d.Name))
+				check.declareObj(pkg.scope, nil, check.lookup(d.Name), token.NoPos)
 			default:
 				check.invalidAST(d.Pos(), "unknown ast.Decl node %T", d)
 			}

go/types/resolver_test.go

@@ -35,7 +35,7 @@ var sources = []string{
 	package p
 	import . "go/parser"
 	import "sync"
-	func g() Mode { return ImportsOnly }
+	func h() Mode { return ImportsOnly }
 	var _, x int = 1, 2
 	func init() {}
 	type T struct{ sync.Mutex; a, b, c int}

go/types/testdata/decls0.src

@@ -69,7 +69,12 @@ type (
 	Pi pi /* ERROR "not a type" */
 
 	a /* ERROR "illegal cycle" */ a
-	a /* ERROR "redeclared" */ int
+	// TODO(gri) For now we get double redeclaration errors if the redeclaration
+	// happens at the package level in the same file. This is because one check
+	// is done in the parser and the other one in the type checker. We cannot
+	// easily avoid this w/o losing the check or functionality. This will be
+	// fixed once all resolution is done in the type checker.
+	a /* ERROR "redeclared" */ /* ERROR "redeclared" */ int
 
 	// where the cycle error appears depends on the
 	// order in which declarations are processed

go/types/testdata/decls1.src

@@ -123,7 +123,6 @@ func (*T) m1() {}
 func (x T) m2() {}
 func (x *T) m3() {}
 
-
 // Initialization functions
 func init() {}
 func /* ERROR "no arguments and no return values" */ init(int) {}

go/types/testdata/decls2a.src

@@ -64,3 +64,9 @@ func (int /* ERROR "non-local type" */ ) m() {}
 func ([ /* ERROR "expected" */ ]int) m() {}
 func (time /* ERROR "expected" */ .Time) m() {}
 func (x interface /* ERROR "expected" */ {}) m() {}
+
+// Double declarations across package files
+const c_double = 0
+type t_double int
+var v_double int
+func f_double() {}

go/types/testdata/decls2b.src

@@ -25,4 +25,10 @@ func (t *T6) m1() int {
 func f() {
 	var t *T6
 	t.m1()
-}
+}
+
+// Double declarations across package files
+const c_double /* ERROR "redeclared" */ = 0
+type t_double  /* ERROR "redeclared" */ int
+var v_double /* ERROR "redeclared" */ int
+func f_double /* ERROR "redeclared" */ () {}