go/internal/gcimporter: prevent importReader reading type parameter twice

This is port of CL 349009 to go/internal/gcimporter.

Updates #48280

Change-Id: I7d40d8b67333538ca58fe012535d54e891d0ed16
Reviewed-on: https://go-review.googlesource.com/c/go/+/349010
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

diff --git a/src/go/internal/gcimporter/iimport.go b/src/go/internal/gcimporter/iimport.go
index 039fc6a61b483cf74e3e92ab55600910968adbbd..56f6418d5e604298b8ead43b8f9c44f38f2f2b23 100644 (file)
--- a/src/go/internal/gcimporter/iimport.go
+++ b/src/go/internal/gcimporter/iimport.go
@@ -284,6 +284,8 @@ type importReader struct {
        prevColumn int64
 }
 
+// obj reads import declaration for an object. It may not read
+// the entire declaration, e.g, for recursive type.
 func (r *importReader) obj(name string) {
        tag := r.byte()
        pos := r.pos()
@@ -309,16 +311,17 @@ func (r *importReader) obj(name string) {
                r.declare(types.NewFunc(pos, r.currPkg, name, sig))
 
        case 'T', 'U':
-               var tparams []*types.TypeParam
-               if tag == 'U' {
-                       tparams = r.tparamList()
-               }
                // Types can be recursive. We need to setup a stub
                // declaration before recursing.
                obj := types.NewTypeName(pos, r.currPkg, name, nil)
                named := types.NewNamed(obj, nil, nil)
-               named.SetTypeParams(tparams)
+               // Declare obj before calling r.tparamList, so the new type name is recognized
+               // if used in the constraint of one of its own typeparams (see #48280).
                r.declare(obj)
+               if tag == 'U' {
+                       tparams := r.tparamList()
+                       named.SetTypeParams(tparams)
+               }
 
                underlying := r.p.typAt(r.uint64(), named).Underlying()
                named.SetUnderlying(underlying)