commit | 37a2290095a78cbe0f0137d3e0d40611f9509ef3 | [log] [tgz] |
---|---|---|
author | Robert Griesemer <gri@golang.org> | Wed Sep 18 16:49:20 2019 -0700 |
committer | Robert Griesemer <gri@golang.org> | Tue Oct 08 16:59:41 2019 +0000 |
tree | 365a309a286da75bb3c2c9fa07506405d94d2171 | |
parent | 816ff44479ae1f1e9459221f63206e93f6f12824 [diff] |
go/types: fix cycle detection For Go 1.13, we rewrote the go/types cycle detection scheme. Unfortunately, it was a bit too clever and introduced a bug (#34333). Here's an example: type A struct { f1 *B f2 B } type B A When type-checking this code, the first cycle A->*B->B->A (via field f1) is ok because there's a pointer indirection. Though in the process B is considered "type-checked" (and painted/marked from "grey" to black"). When type-checking f2, since B is already completely set up, go/types doesn't complain about the invalid cycle A->B->A (via field f2) anymore. On the other hand, with the fields f1, f2 swapped: type A struct { f2 B f1 *B } go/types reports an error because the cycle A->B->A is type-checked first. In general, we cannot know the "right" order in which types need to be type-checked. This CL fixes the issue as follows: 1) The global object path cycle detection does not take (pointer, function, reference type) indirections into account anymore for cycle detection. That mechanism was incorrect to start with and the primary cause for this issue. As a consequence we don't need Checker.indirectType and indir anymore. 2) After processing type declarations, Checker.validType is called to verify that a type doesn't expand indefinitively. This corresponds essentially to cmd/compile's dowidth computation (without size computation). 3) Cycles involving only defined types (e.g.: type (A B; B C; C A)) require separate attention as those must now be detected when resolving "forward chains" of type declarations. Checker.underlying was changed to detect these cycles. All three cycle detection mechanism use an object path ([]Object) to report cycles. The cycle error reporting mechanism is now factored out into Checker.cycleError and used by all three mechanisms. It also makes an attempt to report the cycle starting with the "first" (earliest in the source) object. Fixes #34333. Change-Id: I2c6446445e47344cc2cd034d3c74b1c345b8c1e6 Reviewed-on: https://go-review.googlesource.com/c/go/+/196338 Run-TryBot: Robert Griesemer <gri@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Matthew Dempsky <mdempsky@google.com>
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