1 files changed, 134 insertions, 0 deletions
diff --git a/test/typeparam/nested.go b/test/typeparam/nested.go
new file mode 100644
index 0000000000..c0037a3e6e
--- /dev/null
+++ b/test/typeparam/nested.go
@@ -0,0 +1,134 @@
+// run -gcflags=-G=3
+
+// 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.
+
+// This test case stress tests a number of subtle cases involving
+// nested type-parameterized declarations. At a high-level, it
+// declares a generic function that contains a generic type
+// declaration:
+//
+//	func F[A intish]() {
+//		type T[B intish] struct{}
+//
+//		// store reflect.Type tuple (A, B, F[A].T[B]) in tests
+//	}
+//
+// It then instantiates this function with a variety of type arguments
+// for A and B. Particularly tricky things like shadowed types.
+//
+// From this data it tests two things:
+//
+// 1. Given tuples (A, B, F[A].T[B]) and (A', B', F[A'].T[B']),
+//    F[A].T[B] should be identical to F[A'].T[B'] iff (A, B) is
+//    identical to (A', B').
+//
+// 2. A few of the instantiations are constructed to be identical, and
+//    it tests that exactly these pairs are duplicated (by golden
+//    output comparison to nested.out).
+//
+// In both cases, we're effectively using the compiler's existing
+// runtime.Type handling (which is well tested) of type identity of A
+// and B as a way to help bootstrap testing and validate its new
+// runtime.Type handling of F[A].T[B].
+//
+// This isn't perfect, but it smoked out a handful of issues in
+// gotypes2 and unified IR.
+
+package main
+
+import (
+	"fmt"
+	"reflect"
+)
+
+type test struct {
+	TArgs    [2]reflect.Type
+	Instance reflect.Type
+}
+
+var tests []test
+
+type intish interface{ ~int }
+
+type Int int
+type GlobalInt = Int // allow access to global Int, even when shadowed
+
+func F[A intish]() {
+	add := func(B, T interface{}) {
+		tests = append(tests, test{
+			TArgs: [2]reflect.Type{
+				reflect.TypeOf(A(0)),
+				reflect.TypeOf(B),
+			},
+			Instance: reflect.TypeOf(T),
+		})
+	}
+
+	type Int int
+
+	type T[B intish] struct{}
+
+	add(int(0), T[int]{})
+	add(Int(0), T[Int]{})
+	add(GlobalInt(0), T[GlobalInt]{})
+	add(A(0), T[A]{}) // NOTE: intentionally dups with int and GlobalInt
+
+	type U[_ any] int
+	type V U[int]
+	type W V
+
+	add(U[int](0), T[U[int]]{})
+	add(U[Int](0), T[U[Int]]{})
+	add(U[GlobalInt](0), T[U[GlobalInt]]{})
+	add(U[A](0), T[U[A]]{}) // NOTE: intentionally dups with U[int] and U[GlobalInt]
+	add(V(0), T[V]{})
+	add(W(0), T[W]{})
+}
+
+func main() {
+	type Int int
+
+	F[int]()
+	F[Int]()
+	F[GlobalInt]()
+
+	type U[_ any] int
+	type V U[int]
+	type W V
+
+	F[U[int]]()
+	F[U[Int]]()
+	F[U[GlobalInt]]()
+	F[V]()
+	F[W]()
+
+	type X[A any] U[X[A]]
+
+	F[X[int]]()
+	F[X[Int]]()
+	F[X[GlobalInt]]()
+
+	for j, tj := range tests {
+		for i, ti := range tests[:j+1] {
+			if (ti.TArgs == tj.TArgs) != (ti.Instance == tj.Instance) {
+				fmt.Printf("FAIL: %d,%d: %s, but %s\n", i, j, eq(ti.TArgs, tj.TArgs), eq(ti.Instance, tj.Instance))
+			}
+
+			// The test is constructed so we should see a few identical types.
+			// See "NOTE" comments above.
+			if i != j && ti.Instance == tj.Instance {
+				fmt.Printf("%d,%d: %v\n", i, j, ti.Instance)
+			}
+		}
+	}
+}
+
+func eq(a, b interface{}) string {
+	op := "=="
+	if a != b {
+		op = "!="
+	}
+	return fmt.Sprintf("%v %s %v", a, op, b)
+}