context_test.go

Documentation: cmd/compile/internal/types2

     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  
     5  package types2
     6  
     7  import (
     8  	"testing"
     9  )
    10  
    11  func TestContextHashCollisions(t *testing.T) {
    12  	if debug {
    13  		t.Skip("hash collisions are expected, and would fail debug assertions")
    14  	}
    15  	// Unit test the de-duplication fall-back logic in Context.
    16  	//
    17  	// We can't test this via Instantiate because this is only a fall-back in
    18  	// case our hash is imperfect.
    19  	//
    20  	// These lookups and updates use reasonable looking types in an attempt to
    21  	// make them robust to internal type assertions, but could equally well use
    22  	// arbitrary types.
    23  
    24  	// Create some distinct origin types. nullaryP and nullaryQ have no
    25  	// parameters and are identical (but have different type parameter names).
    26  	// unaryP has a parameter.
    27  	var nullaryP, nullaryQ, unaryP Type
    28  	{
    29  		// type nullaryP = func[P any]()
    30  		tparam := NewTypeParam(NewTypeName(nopos, nil, "P", nil), &emptyInterface)
    31  		nullaryP = NewSignatureType(nil, nil, []*TypeParam{tparam}, nil, nil, false)
    32  	}
    33  	{
    34  		// type nullaryQ = func[Q any]()
    35  		tparam := NewTypeParam(NewTypeName(nopos, nil, "Q", nil), &emptyInterface)
    36  		nullaryQ = NewSignatureType(nil, nil, []*TypeParam{tparam}, nil, nil, false)
    37  	}
    38  	{
    39  		// type unaryP = func[P any](_ P)
    40  		tparam := NewTypeParam(NewTypeName(nopos, nil, "P", nil), &emptyInterface)
    41  		params := NewTuple(NewVar(nopos, nil, "_", tparam))
    42  		unaryP = NewSignatureType(nil, nil, []*TypeParam{tparam}, params, nil, false)
    43  	}
    44  
    45  	ctxt := NewContext()
    46  
    47  	// Update the context with an instantiation of nullaryP.
    48  	inst := NewSignatureType(nil, nil, nil, nil, nil, false)
    49  	if got := ctxt.update("", nullaryP, []Type{Typ[Int]}, inst); got != inst {
    50  		t.Error("bad")
    51  	}
    52  
    53  	// unaryP is not identical to nullaryP, so we should not get inst when
    54  	// instantiated with identical type arguments.
    55  	if got := ctxt.lookup("", unaryP, []Type{Typ[Int]}); got != nil {
    56  		t.Error("bad")
    57  	}
    58  
    59  	// nullaryQ is identical to nullaryP, so we *should* get inst when
    60  	// instantiated with identical type arguments.
    61  	if got := ctxt.lookup("", nullaryQ, []Type{Typ[Int]}); got != inst {
    62  		t.Error("bad")
    63  	}
    64  
    65  	// ...but verify we don't get inst with different type arguments.
    66  	if got := ctxt.lookup("", nullaryQ, []Type{Typ[String]}); got != nil {
    67  		t.Error("bad")
    68  	}
    69  }
    70
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