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go/test/fixedbugs/issue24939.go
Robert Griesemer 48987baa09 cmd/compile: correct alias cycle detection
The original fix (https://go-review.googlesource.com/c/go/+/35831)
for this issue was incorrect as it reported cycles in cases where
it shouldn't.

Instead, use a different approach: A type cycle containing aliases
is only a cycle if there are no type definitions. As soon as there
is a type definition, alias expansion terminates and there is no
cycle.

Approach: Split sprint_depchain into two non-recursive and more
easily understandable functions (cycleFor and cycleTrace),
and use those instead for cycle reporting. Analyze the cycle
returned by cycleFor before issueing an alias cycle error.

Also: Removed original fix (main.go) which introduced a separate
crash (#23823).

Fixes #18640.
Fixes #23823.
Fixes #24939.

Change-Id: Ic3707a9dec40a71dc928a3e49b4868c5fac3d3b7
Reviewed-on: https://go-review.googlesource.com/118078
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
2018-06-12 18:55:39 +00:00

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Go

// compile
// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
type T interface {
M(P)
}
type M interface {
F() P
}
type P = interface {
I() M
}
func main() {}