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go/types: avoid endless recursion in the Comparable predicate

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This is a port of CL 276374 from the dev.typeparams branch. Avoid an
endless recursion in Comparable by tracking types that have already been
considered.

Fixes #43088

Change-Id: I927b29ac544df9bfb5c8c04699d57fafe6cfff73
Reviewed-on: https://go-review.googlesource.com/c/go/+/276552
Run-TryBot: Robert Findley <rfindley@google.com>
Trust: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
This commit is contained in:
Rob Findley 2020-12-09 06:10:52 -05:00 committed by Robert Findley
parent f1980efb92
commit 89f465c2b5
2 changed files with 40 additions and 2 deletions
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26
src/go/types/issues_test.go
View File

@ -12,6 +12,7 @@ import (
"go/ast"
"go/importer"
"go/parser"
"go/token"
"internal/testenv"
"sort"
"strings"
@ -523,3 +524,28 @@ 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 {
// _ T2
// }
//
// type T2 struct {
// _ struct {
// _ T2
// }
// }
n1 := NewTypeName(token.NoPos, nil, "T1", nil)
T1 := NewNamed(n1, nil, nil)
n2 := NewTypeName(token.NoPos, nil, "T2", nil)
T2 := NewNamed(n2, nil, nil)
s1 := NewStruct([]*Var{NewField(token.NoPos, nil, "_", T2, false)}, nil)
T1.SetUnderlying(s1)
s2 := NewStruct([]*Var{NewField(token.NoPos, nil, "_", T2, false)}, nil)
s3 := NewStruct([]*Var{NewField(token.NoPos, nil, "_", s2, false)}, nil)
T2.SetUnderlying(s3)
// These calls must terminate (no endless recursion).
Comparable(T1)
Comparable(T2)
}

16
src/go/types/predicates.go
View File

@ -79,6 +79,18 @@ func IsInterface(typ Type) bool {
// Comparable reports whether values of type T are comparable.
func Comparable(T Type) bool {
return comparable(T, nil)
}
func comparable(T Type, seen map[Type]bool) bool {
if seen[T] {
return true
}
if seen == nil {
seen = make(map[Type]bool)
}
seen[T] = true
switch t := T.Underlying().(type) {
case *Basic:
// assume invalid types to be comparable
@ -88,13 +100,13 @@ 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)
}
return false
}