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[dev.typeparams] cmd/compile/internal/types2: avoid endless recursion in Comparable predicate
Use a map to detect recursive types. With this we can now typecheck fixedbugs/issue8501.go. Updates #43088. Change-Id: I7fad6ccf6c94268473ff72b09a3158e13a7f4cc3 Reviewed-on: https://go-review.googlesource.com/c/go/+/276374 Trust: Robert Griesemer <gri@golang.org> Run-TryBot: Robert Griesemer <gri@golang.org> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Robert Findley <rfindley@google.com>
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@ -531,3 +531,28 @@ func TestIssue34921(t *testing.T) {
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pkg = res // res is imported by the next package in this test
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}
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}
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func TestIssue43088(t *testing.T) {
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// type T1 struct {
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// x T2
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// }
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//
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// type T2 struct {
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// x struct {
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// x T2
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// }
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// }
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n1 := NewTypeName(syntax.Pos{}, nil, "T1", nil)
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T1 := NewNamed(n1, nil, nil)
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n2 := NewTypeName(syntax.Pos{}, nil, "T2", nil)
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T2 := NewNamed(n2, nil, nil)
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s1 := NewStruct([]*Var{NewField(syntax.Pos{}, nil, "x", T2, false)}, nil)
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T1.SetUnderlying(s1)
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s2 := NewStruct([]*Var{NewField(syntax.Pos{}, nil, "x", T2, false)}, nil)
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s3 := NewStruct([]*Var{NewField(syntax.Pos{}, nil, "x", s2, false)}, nil)
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T2.SetUnderlying(s3)
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// These calls must terminate (no endless recursion).
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Comparable(T1)
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Comparable(T2)
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}
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@ -87,6 +87,11 @@ func IsInterface(typ Type) bool {
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// Comparable reports whether values of type T are comparable.
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func Comparable(T Type) bool {
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return comparable(T, nil)
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}
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// comparable should only be called by Comparable.
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func comparable(T Type, seen map[Type]bool) bool {
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// If T is a type parameter not constraint by any type
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// list (i.e., it's underlying type is the top type),
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// T is comparable if it has the == method. Otherwise,
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@ -99,6 +104,14 @@ func Comparable(T Type) bool {
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return t.Bound().IsComparable()
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}
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if seen[T] {
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return true
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}
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if seen == nil {
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seen = make(map[Type]bool)
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}
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seen[T] = true
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switch t := optype(T.Under()).(type) {
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case *Basic:
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// assume invalid types to be comparable
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@ -108,13 +121,13 @@ func Comparable(T Type) bool {
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return true
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case *Struct:
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for _, f := range t.fields {
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if !Comparable(f.typ) {
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if !comparable(f.typ, seen) {
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return false
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}
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}
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return true
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case *Array:
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return Comparable(t.elem)
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return comparable(t.elem, seen)
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case *Sum:
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return t.is(Comparable)
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case *TypeParam:
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@ -9,7 +9,7 @@
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package p
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type T struct{ T } // ERROR "invalid recursive type T"
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type T struct{ T } // ERROR "invalid recursive type T|cycle"
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func f() {
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println(T{} == T{})
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@ -2130,6 +2130,4 @@ var excluded = map[string]bool{
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"fixedbugs/issue7525e.go": true,
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"fixedbugs/issue7742.go": true, // type-checking doesn't terminate
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"fixedbugs/issue7746.go": true, // type-checking doesn't terminate
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"fixedbugs/issue8501.go": true, // crashes
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"fixedbugs/issue8507.go": true, // crashes
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}
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