[release-branch.go1.18] go/types, types2: preserve parent scope when substituting receivers

For #51920
Fixes #52007

Change-Id: I29e44a52dabee5c09e1761f9ec8fb2e8795f8901
Reviewed-on: https://go-review.googlesource.com/c/go/+/395538
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
(cherry picked from commit 9b90838712856cad86504a526e566f963f86c04e)
Reviewed-on: https://go-review.googlesource.com/c/go/+/395680

6 files changed, 215 insertions, 14 deletions

diff --git a/src/cmd/compile/internal/types2/api_test.go b/src/cmd/compile/internal/types2/api_test.go
index 5bb551798e..dae39ad92c 100644
--- a/src/cmd/compile/internal/types2/api_test.go
+++ b/src/cmd/compile/internal/types2/api_test.go
@@ -2288,6 +2288,103 @@ func TestInstanceIdentity(t *testing.T) {
 	}
 }
 
+// TestInstantiatedObjects verifies properties of instantiated objects.
+func TestInstantiatedObjects(t *testing.T) {
+	const src = `
+package p
+
+type T[P any] struct {
+	field P
+}
+
+func (recv *T[Q]) concreteMethod() {}
+
+type FT[P any] func(ftp P) (ftrp P)
+
+func F[P any](fp P) (frp P){ return }
+
+type I[P any] interface {
+	interfaceMethod(P)
+}
+
+var (
+	t T[int]
+	ft FT[int]
+	f = F[int]
+	i I[int]
+)
+`
+	info := &Info{
+		Defs: make(map[*syntax.Name]Object),
+	}
+	f, err := parseSrc("p.go", src)
+	if err != nil {
+		t.Fatal(err)
+	}
+	conf := Config{}
+	pkg, err := conf.Check(f.PkgName.Value, []*syntax.File{f}, info)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	lookup := func(name string) Type { return pkg.Scope().Lookup(name).Type() }
+	tests := []struct {
+		ident string
+		obj   Object
+	}{
+		{"field", lookup("t").Underlying().(*Struct).Field(0)},
+		{"concreteMethod", lookup("t").(*Named).Method(0)},
+		{"recv", lookup("t").(*Named).Method(0).Type().(*Signature).Recv()},
+		{"ftp", lookup("ft").Underlying().(*Signature).Params().At(0)},
+		{"ftrp", lookup("ft").Underlying().(*Signature).Results().At(0)},
+		{"fp", lookup("f").(*Signature).Params().At(0)},
+		{"frp", lookup("f").(*Signature).Results().At(0)},
+		{"interfaceMethod", lookup("i").Underlying().(*Interface).Method(0)},
+	}
+
+	// Collect all identifiers by name.
+	idents := make(map[string][]*syntax.Name)
+	syntax.Inspect(f, func(n syntax.Node) bool {
+		if id, ok := n.(*syntax.Name); ok {
+			idents[id.Value] = append(idents[id.Value], id)
+		}
+		return true
+	})
+
+	for _, test := range tests {
+		test := test
+		t.Run(test.ident, func(t *testing.T) {
+			if got := len(idents[test.ident]); got != 1 {
+				t.Fatalf("found %d identifiers named %s, want 1", got, test.ident)
+			}
+			ident := idents[test.ident][0]
+			def := info.Defs[ident]
+			if def == test.obj {
+				t.Fatalf("info.Defs[%s] contains the test object", test.ident)
+			}
+			if def.Pkg() != test.obj.Pkg() {
+				t.Errorf("Pkg() = %v, want %v", def.Pkg(), test.obj.Pkg())
+			}
+			if def.Name() != test.obj.Name() {
+				t.Errorf("Name() = %v, want %v", def.Name(), test.obj.Name())
+			}
+			if def.Pos() != test.obj.Pos() {
+				t.Errorf("Pos() = %v, want %v", def.Pos(), test.obj.Pos())
+			}
+			if def.Parent() != test.obj.Parent() {
+				t.Fatalf("Parent() = %v, want %v", def.Parent(), test.obj.Parent())
+			}
+			if def.Exported() != test.obj.Exported() {
+				t.Fatalf("Exported() = %v, want %v", def.Exported(), test.obj.Exported())
+			}
+			if def.Id() != test.obj.Id() {
+				t.Fatalf("Id() = %v, want %v", def.Id(), test.obj.Id())
+			}
+			// String and Type are expected to differ.
+		})
+	}
+}
+
 func TestImplements(t *testing.T) {
 	const src = `
 package p
diff --git a/src/cmd/compile/internal/types2/named.go b/src/cmd/compile/internal/types2/named.go
index daf8fdc986..8a936ebcec 100644
--- a/src/cmd/compile/internal/types2/named.go
+++ b/src/cmd/compile/internal/types2/named.go
@@ -190,7 +190,7 @@ func (t *Named) instantiateMethod(i int) *Func {
 		rtyp = t
 	}
 
-	sig.recv = NewParam(origSig.recv.pos, origSig.recv.pkg, origSig.recv.name, rtyp)
+	sig.recv = substVar(origSig.recv, rtyp)
 	return NewFunc(origm.pos, origm.pkg, origm.name, sig)
 }
 
diff --git a/src/cmd/compile/internal/types2/subst.go b/src/cmd/compile/internal/types2/subst.go
index 037f04797b..c9e8f9676d 100644
--- a/src/cmd/compile/internal/types2/subst.go
+++ b/src/cmd/compile/internal/types2/subst.go
@@ -290,14 +290,18 @@ func (subst *subster) typOrNil(typ Type) Type {
 func (subst *subster) var_(v *Var) *Var {
 	if v != nil {
 		if typ := subst.typ(v.typ); typ != v.typ {
-			copy := *v
-			copy.typ = typ
-			return &copy
+			return substVar(v, typ)
 		}
 	}
 	return v
 }
 
+func substVar(v *Var, typ Type) *Var {
+	copy := *v
+	copy.typ = typ
+	return &copy
+}
+
 func (subst *subster) tuple(t *Tuple) *Tuple {
 	if t != nil {
 		if vars, copied := subst.varList(t.vars); copied {
@@ -410,9 +414,8 @@ func replaceRecvType(in []*Func, old, new Type) (out []*Func, copied bool) {
 				copied = true
 			}
 			newsig := *sig
-			sig = &newsig
-			sig.recv = NewVar(sig.recv.pos, sig.recv.pkg, "", new)
-			out[i] = NewFunc(method.pos, method.pkg, method.name, sig)
+			newsig.recv = substVar(sig.recv, new)
+			out[i] = NewFunc(method.pos, method.pkg, method.name, &newsig)
 		}
 	}
 	return
diff --git a/src/go/types/api_test.go b/src/go/types/api_test.go
index 4014201769..6b05d66b10 100644
--- a/src/go/types/api_test.go
+++ b/src/go/types/api_test.go
@@ -2288,6 +2288,104 @@ func TestInstanceIdentity(t *testing.T) {
 	}
 }
 
+// TestInstantiatedObjects verifies properties of instantiated objects.
+func TestInstantiatedObjects(t *testing.T) {
+	const src = `
+package p
+
+type T[P any] struct {
+	field P
+}
+
+func (recv *T[Q]) concreteMethod() {}
+
+type FT[P any] func(ftp P) (ftrp P)
+
+func F[P any](fp P) (frp P){ return }
+
+type I[P any] interface {
+	interfaceMethod(P)
+}
+
+var (
+	t T[int]
+	ft FT[int]
+	f = F[int]
+	i I[int]
+)
+`
+	info := &Info{
+		Defs: make(map[*ast.Ident]Object),
+	}
+	fset := token.NewFileSet()
+	f, err := parser.ParseFile(fset, "p.go", src, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	conf := Config{}
+	pkg, err := conf.Check(f.Name.Name, fset, []*ast.File{f}, info)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	lookup := func(name string) Type { return pkg.Scope().Lookup(name).Type() }
+	tests := []struct {
+		name string
+		obj  Object
+	}{
+		{"field", lookup("t").Underlying().(*Struct).Field(0)},
+		{"concreteMethod", lookup("t").(*Named).Method(0)},
+		{"recv", lookup("t").(*Named).Method(0).Type().(*Signature).Recv()},
+		{"ftp", lookup("ft").Underlying().(*Signature).Params().At(0)},
+		{"ftrp", lookup("ft").Underlying().(*Signature).Results().At(0)},
+		{"fp", lookup("f").(*Signature).Params().At(0)},
+		{"frp", lookup("f").(*Signature).Results().At(0)},
+		{"interfaceMethod", lookup("i").Underlying().(*Interface).Method(0)},
+	}
+
+	// Collect all identifiers by name.
+	idents := make(map[string][]*ast.Ident)
+	ast.Inspect(f, func(n ast.Node) bool {
+		if id, ok := n.(*ast.Ident); ok {
+			idents[id.Name] = append(idents[id.Name], id)
+		}
+		return true
+	})
+
+	for _, test := range tests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			if got := len(idents[test.name]); got != 1 {
+				t.Fatalf("found %d identifiers named %s, want 1", got, test.name)
+			}
+			ident := idents[test.name][0]
+			def := info.Defs[ident]
+			if def == test.obj {
+				t.Fatalf("info.Defs[%s] contains the test object", test.name)
+			}
+			if def.Pkg() != test.obj.Pkg() {
+				t.Errorf("Pkg() = %v, want %v", def.Pkg(), test.obj.Pkg())
+			}
+			if def.Name() != test.obj.Name() {
+				t.Errorf("Name() = %v, want %v", def.Name(), test.obj.Name())
+			}
+			if def.Pos() != test.obj.Pos() {
+				t.Errorf("Pos() = %v, want %v", def.Pos(), test.obj.Pos())
+			}
+			if def.Parent() != test.obj.Parent() {
+				t.Fatalf("Parent() = %v, want %v", def.Parent(), test.obj.Parent())
+			}
+			if def.Exported() != test.obj.Exported() {
+				t.Fatalf("Exported() = %v, want %v", def.Exported(), test.obj.Exported())
+			}
+			if def.Id() != test.obj.Id() {
+				t.Fatalf("Id() = %v, want %v", def.Id(), test.obj.Id())
+			}
+			// String and Type are expected to differ.
+		})
+	}
+}
+
 func TestImplements(t *testing.T) {
 	const src = `
 package p
diff --git a/src/go/types/named.go b/src/go/types/named.go
index 876f7e8551..e60b229bb3 100644
--- a/src/go/types/named.go
+++ b/src/go/types/named.go
@@ -192,7 +192,7 @@ func (t *Named) instantiateMethod(i int) *Func {
 		rtyp = t
 	}
 
-	sig.recv = NewParam(origSig.recv.pos, origSig.recv.pkg, origSig.recv.name, rtyp)
+	sig.recv = substVar(origSig.recv, rtyp)
 	return NewFunc(origm.pos, origm.pkg, origm.name, sig)
 }
 
diff --git a/src/go/types/subst.go b/src/go/types/subst.go
index 4b4a0f4ad6..ef5593b71f 100644
--- a/src/go/types/subst.go
+++ b/src/go/types/subst.go
@@ -290,14 +290,18 @@ func (subst *subster) typOrNil(typ Type) Type {
 func (subst *subster) var_(v *Var) *Var {
 	if v != nil {
 		if typ := subst.typ(v.typ); typ != v.typ {
-			copy := *v
-			copy.typ = typ
-			return &copy
+			return substVar(v, typ)
 		}
 	}
 	return v
 }
 
+func substVar(v *Var, typ Type) *Var {
+	copy := *v
+	copy.typ = typ
+	return &copy
+}
+
 func (subst *subster) tuple(t *Tuple) *Tuple {
 	if t != nil {
 		if vars, copied := subst.varList(t.vars); copied {
@@ -410,9 +414,8 @@ func replaceRecvType(in []*Func, old, new Type) (out []*Func, copied bool) {
 				copied = true
 			}
 			newsig := *sig
-			sig = &newsig
-			sig.recv = NewVar(sig.recv.pos, sig.recv.pkg, "", new)
-			out[i] = NewFunc(method.pos, method.pkg, method.name, sig)
+			newsig.recv = substVar(sig.recv, new)
+			out[i] = NewFunc(method.pos, method.pkg, method.name, &newsig)
 		}
 	}
 	return