[release-branch.go1.22] go/types, types2: ensure that Alias.actual is…

… set in NewAlias Types returned by the go/types API must be immutable (or at least concurrency safe), but NewAlias returned an alias without actual set. Ensure that actual is set by unaliasing. Also make some superficial simplifications to unalias, and avoid indirection where unnecessary. Fixes #65728 Change-Id: Ic9a020da5accf9032056a924b65c9e9e08cb2e0a Reviewed-on: https://go-review.googlesource.com/c/go/+/560915 LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com> Reviewed-by: Robert Griesemer <gri@google.com> (cherry picked from commit 10a6564) Reviewed-on: https://go-review.googlesource.com/c/go/+/564356
golang · Feb 27, 2024 · 3b71998 · 3b71998
1 parent 8fe2ad6
commit 3b71998
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Showing 4 changed files with 54 additions and 32 deletions.
diff --git a/src/cmd/compile/internal/types2/alias.go b/src/cmd/compile/internal/types2/alias.go
@@ -21,11 +21,14 @@ type Alias struct {
 // NewAlias creates a new Alias type with the given type name and rhs.
 // rhs must not be nil.
 func NewAlias(obj *TypeName, rhs Type) *Alias {
-	return (*Checker)(nil).newAlias(obj, rhs)
+	alias := (*Checker)(nil).newAlias(obj, rhs)
+	// Ensure that alias.actual is set (#65455).
+	unalias(alias)
+	return alias
 }
 
 func (a *Alias) Obj() *TypeName   { return a.obj }
-func (a *Alias) Underlying() Type { return a.actual.Underlying() }
+func (a *Alias) Underlying() Type { return unalias(a).Underlying() }
 func (a *Alias) String() string   { return TypeString(a, nil) }
 
 // Type accessors
@@ -36,24 +39,26 @@ func (a *Alias) String() string   { return TypeString(a, nil) }
 // Consequently, the result is never an alias type.
 func Unalias(t Type) Type {
 	if a0, _ := t.(*Alias); a0 != nil {
-		if a0.actual != nil {
-			return a0.actual
-		}
-		for a := a0; ; {
-			t = a.fromRHS
-			a, _ = t.(*Alias)
-			if a == nil {
-				break
-			}
-		}
-		if t == nil {
-			panic(fmt.Sprintf("non-terminated alias %s", a0.obj.name))
-		}
-		a0.actual = t
+		return unalias(a0)
 	}
 	return t
 }
 
+func unalias(a0 *Alias) Type {
+	if a0.actual != nil {
+		return a0.actual
+	}
+	var t Type
+	for a := a0; a != nil; a, _ = t.(*Alias) {
+		t = a.fromRHS
+	}
+	if t == nil {
+		panic(fmt.Sprintf("non-terminated alias %s", a0.obj.name))
+	}
+	a0.actual = t
+	return t
+}
+
 // asNamed returns t as *Named if that is t's
 // actual type. It returns nil otherwise.
 func asNamed(t Type) *Named {

diff --git a/src/cmd/compile/internal/types2/api_test.go b/src/cmd/compile/internal/types2/api_test.go
@@ -2195,6 +2195,12 @@ func TestIssue61737(t *testing.T) {
 	iface.NumMethods() // unlike go/types, there is no Complete() method, so we complete implicitly
 }
 
+func TestNewAlias_Issue65455(t *testing.T) {
+	obj := NewTypeName(nopos, nil, "A", nil)
+	alias := NewAlias(obj, Typ[Int])
+	alias.Underlying() // must not panic
+}
+
 func TestIssue15305(t *testing.T) {
 	const src = "package p; func f() int16; var _ = f(undef)"
 	f := mustParse(src)

diff --git a/src/go/types/alias.go b/src/go/types/alias.go
diff --git a/src/go/types/api_test.go b/src/go/types/api_test.go
@@ -2196,6 +2196,12 @@ func TestIssue61737(t *testing.T) {
 	iface.Complete()
 }
 
+func TestNewAlias_Issue65455(t *testing.T) {
+	obj := NewTypeName(nopos, nil, "A", nil)
+	alias := NewAlias(obj, Typ[Int])
+	alias.Underlying() // must not panic
+}
+
 func TestIssue15305(t *testing.T) {
 	const src = "package p; func f() int16; var _ = f(undef)"
 	fset := token.NewFileSet()