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[dev.go2go] go/types: avoid endless recursion in self-recursive newty… #40051

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[dev.go2go] go/types: avoid endless recursion in self-recursive newty… #40051

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1 change: 1 addition & 0 deletions src/go/types/check_test.go
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Expand Up @@ -140,6 +140,7 @@ var tests = [][]string{
{"fixedbugs/issue39948.go2"},
{"fixedbugs/issue39976.go2"},
{"fixedbugs/issue39982.go2"},
{"fixedbugs/issue40037.go2"},
}

var fset = token.NewFileSet()
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10 changes: 10 additions & 0 deletions src/go/types/fixedbugs/issue40037.go2
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@@ -0,0 +1,10 @@
package main

// from issue #40037
type comp(type T comparable) T
type K /* ERROR illegal cycle */ comp(K) // becomes 'type K K', where K is comparable

// from issue #39634 crash 22
type T(type _ interface{ a() }) int
type A(type P) T(A(int))

8 changes: 8 additions & 0 deletions src/go/types/subst.go
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Expand Up @@ -142,6 +142,14 @@ func (check *Checker) instantiate(pos token.Pos, typ Type, targs []Type, poslist
// - check only if we have methods
check.completeInterface(token.NoPos, iface)
if len(iface.allMethods) > 0 {
// Break cycle in cases like
//
// type constr(type T comparable) T
// type K constr(K)
if t1 := typ.Named(); t1 != nil && t1.underlying == t1.orig {
break
}

// If the type argument is a type parameter itself, its pointer designation
// must match the pointer designation of the callee's type parameter.
// If the type argument is a pointer to a type parameter, the type argument's
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