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Robert Griesemer 07eca49055 go/types, types2: use type nest to detect type cycles (fix validType)
validType was using a global type info map to detect invalid recursive
types, which was incorrect. Instead, change the algorithm as follows:

- Rather than using a "seen" (or typeInfo) map which is cumbersome to
  update correctly, use the stack of embedding types (the type nest)
  to check whether a type is embedded within itself, directly or
  indirectly.

- Use Identical for type comparisons which correctly considers identity
  of instantiated generic types.

- As before, maintain the full path of types leading to a cycle. But
  unlike before, track the named types rather than their objects, for
  a smaller slice ([]*Named rather than []Object), and convert to an
  object list only when needed for error reporting.

- As an optimization, keep track of valid *Named types (Checker.valids).
  This prevents pathological cases from consuming excessive computation
  time.

- Add clarifying comments and document invariants.

Based on earlier insights by David Chase (see also CL 408818).

Fixes #52698.

Change-Id: I5e4598c58afcf4ab987a426c5c4b7b28bdfcf5ea
Reviewed-on: https://go-review.googlesource.com/c/go/+/409694
Reviewed-by: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
2022-06-06 18:24:19 +00:00
.github
api io: revert: add an Err field to LimitedReader 2022-06-04 14:00:38 +00:00
doc doc/go1.19: add TODOs for changes to go/types 2022-06-06 16:26:54 +00:00
lib/time
misc
src go/types, types2: use type nest to detect type cycles (fix validType) 2022-06-06 18:24:19 +00:00
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