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[dev.typeparams] cmd/compile/internal/types2: avoid endless recursion in Comparable predicate

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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>
This commit is contained in:
Robert Griesemer 2020-12-08 16:58:00 -08:00
parent 6015c4e543
commit c32566c336
4 changed files with 41 additions and 5 deletions
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25
src/cmd/compile/internal/types2/issues_test.go
View File

@ -531,3 +531,28 @@ func TestIssue34921(t *testing.T) {
pkg = res // res is imported by the next package in this test
}
}
func TestIssue43088(t *testing.T) {
// type T1 struct {
// x T2
// }
//
// type T2 struct {
// x struct {
// x T2
// }
// }
n1 := NewTypeName(syntax.Pos{}, nil, "T1", nil)
T1 := NewNamed(n1, nil, nil)
n2 := NewTypeName(syntax.Pos{}, nil, "T2", nil)
T2 := NewNamed(n2, nil, nil)
s1 := NewStruct([]*Var{NewField(syntax.Pos{}, nil, "x", T2, false)}, nil)
T1.SetUnderlying(s1)
s2 := NewStruct([]*Var{NewField(syntax.Pos{}, nil, "x", T2, false)}, nil)
s3 := NewStruct([]*Var{NewField(syntax.Pos{}, nil, "x", s2, false)}, nil)
T2.SetUnderlying(s3)
// These calls must terminate (no endless recursion).
Comparable(T1)
Comparable(T2)
}

17
src/cmd/compile/internal/types2/predicates.go
View File

@ -87,6 +87,11 @@ func IsInterface(typ Type) bool {
// Comparable reports whether values of type T are comparable.
func Comparable(T Type) bool {
return comparable(T, nil)
}
// comparable should only be called by Comparable.
func comparable(T Type, seen map[Type]bool) bool {
// If T is a type parameter not constraint by any type
// list (i.e., it's underlying type is the top type),
// T is comparable if it has the == method. Otherwise,
@ -99,6 +104,14 @@ func Comparable(T Type) bool {
return t.Bound().IsComparable()
}
if seen[T] {
return true
}
if seen == nil {
seen = make(map[Type]bool)
}
seen[T] = true
switch t := optype(T.Under()).(type) {
case *Basic:
// assume invalid types to be comparable
@ -108,13 +121,13 @@ func Comparable(T Type) bool {
return true
case *Struct:
for _, f := range t.fields {
if !Comparable(f.typ) {
if !comparable(f.typ, seen) {
return false
}
}
return true
case *Array:
return Comparable(t.elem)
return comparable(t.elem, seen)
case *Sum:
return t.is(Comparable)
case *TypeParam:

2
test/fixedbugs/issue8507.go
View File

@ -9,7 +9,7 @@
package p
type T struct{ T } // ERROR "invalid recursive type T"
type T struct{ T } // ERROR "invalid recursive type T|cycle"
func f() {
println(T{} == T{})

2
test/run.go
View File

@ -2130,6 +2130,4 @@ var excluded = map[string]bool{
"fixedbugs/issue7525e.go": true,
"fixedbugs/issue7742.go": true, // type-checking doesn't terminate
"fixedbugs/issue7746.go": true, // type-checking doesn't terminate
"fixedbugs/issue8501.go": true, // crashes
"fixedbugs/issue8507.go": true, // crashes
}