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The type checker doesn't have a general mechanism to "use" the type of a type alias whose type depends on a recursive type declaration which is not yet completely type-checked. In some cases, the type of a type alias is needed before it is determined; the type is incorrect (invalid) in that case but no error is reported. The type-checker is happy with this (incorrect type), but the compiler may crash under some circumstances. A correct fix will likely require some form of forwarding type which is a fairly pervasive change and may also affect the type checker API. This CL introduces a simple side table, a map of broken type aliases, which is consulted before the type associated with a type alias is used. If the type alias is broken, an error is reported. This is a stop-gap solution that prevents the compiler from crashing. The reported error refers to the corresponding issue which suggests a work-around that may be applicable in some cases. Also fix a minor error related to type cycles: If we have a cycle that doesn't start with a type, don't use a compiler error message that explicitly mentions "type". Fixes #50259. Fixes #50276. Fixes #50779. For #50729. Change-Id: Ie8e38f49ef724e742e8e78625e6d4f3d4014a52c Reviewed-on: https://go-review.googlesource.com/c/go/+/379916 Trust: Robert Griesemer <gri@golang.org> Run-TryBot: Robert Griesemer <gri@golang.org> Reviewed-by: Robert Findley <rfindley@google.com> TryBot-Result: Gopher Robot <gobot@golang.org>
14 lines
309 B
Go
14 lines
309 B
Go
// errorcheck -G=3
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// Copyright 2022 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package p
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var x T[B]
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type T[_ any] struct{}
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type A T[B] // ERROR "invalid use of type alias B in recursive type"
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type B = T[A]
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