1// Copyright 2021 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package types
6
7import (
8	"go/token"
9	"testing"
10)
11
12func TestContextHashCollisions(t *testing.T) {
13	if debug {
14		t.Skip("hash collisions are expected, and would fail debug assertions")
15	}
16	// Unit test the de-duplication fall-back logic in Context.
17	//
18	// We can't test this via Instantiate because this is only a fall-back in
19	// case our hash is imperfect.
20	//
21	// These lookups and updates use reasonable looking types in an attempt to
22	// make them robust to internal type assertions, but could equally well use
23	// arbitrary types.
24
25	// Create some distinct origin types. nullaryP and nullaryQ have no
26	// parameters and are identical (but have different type parameter names).
27	// unaryP has a parameter.
28	var nullaryP, nullaryQ, unaryP Type
29	{
30		// type nullaryP = func[P any]()
31		tparam := NewTypeParam(NewTypeName(token.NoPos, nil, "P", nil), &emptyInterface)
32		nullaryP = NewSignatureType(nil, nil, []*TypeParam{tparam}, nil, nil, false)
33	}
34	{
35		// type nullaryQ = func[Q any]()
36		tparam := NewTypeParam(NewTypeName(token.NoPos, nil, "Q", nil), &emptyInterface)
37		nullaryQ = NewSignatureType(nil, nil, []*TypeParam{tparam}, nil, nil, false)
38	}
39	{
40		// type unaryP = func[P any](_ P)
41		tparam := NewTypeParam(NewTypeName(token.NoPos, nil, "P", nil), &emptyInterface)
42		params := NewTuple(NewVar(token.NoPos, nil, "_", tparam))
43		unaryP = NewSignatureType(nil, nil, []*TypeParam{tparam}, params, nil, false)
44	}
45
46	ctxt := NewContext()
47
48	// Update the context with an instantiation of nullaryP.
49	inst := NewSignatureType(nil, nil, nil, nil, nil, false)
50	if got := ctxt.update("", nullaryP, []Type{Typ[Int]}, inst); got != inst {
51		t.Error("bad")
52	}
53
54	// unaryP is not identical to nullaryP, so we should not get inst when
55	// instantiated with identical type arguments.
56	if got := ctxt.lookup("", unaryP, []Type{Typ[Int]}); got != nil {
57		t.Error("bad")
58	}
59
60	// nullaryQ is identical to nullaryP, so we *should* get inst when
61	// instantiated with identical type arguments.
62	if got := ctxt.lookup("", nullaryQ, []Type{Typ[Int]}); got != inst {
63		t.Error("bad")
64	}
65
66	// ...but verify we don't get inst with different type arguments.
67	if got := ctxt.lookup("", nullaryQ, []Type{Typ[String]}); got != nil {
68		t.Error("bad")
69	}
70}
71