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Fix infinite loop in List: expander in subtyping

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The match expander calls `resolve` during subtyping, which
is a problem for types that recur through the environment like
Struct types because it doesn't coordinate with the cache
for subtyping.

Closes PR 14364

original commit: 7585581f00a40f59d5f29159622a10640cfbdec9
This commit is contained in:
Asumu Takikawa 2014-02-24 17:14:42 -05:00
parent c26f9b4c73
commit 2dd8725cbd
2 changed files with 18 additions and 2 deletions
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13
pkgs/typed-racket-pkgs/typed-racket-lib/typed-racket/types/subtype.rkt
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@ -310,8 +310,17 @@
(subtype* t1 t*)
(subtype* t2 (simple-Un (-val null) (make-MPairTop)))
(subtype* t2 t))]
[((List: ts) (Sequence: (list t*)))
(subtypes* A0 ts (map (λ (_) t*) ts))]
;; Note: this next case previously used the List: match expander, but
;; using that would cause an infinite loop in certain cases
;; (i.e., Struct types, see PR 14364) because the expander
;; uses `resolve`. This is not normally a problem, but during
;; subtyping it's dangerous to call functions that can cause
;; substitution and thus more subtyping checks.
;;
;; Instead, we can just check for Null here since combined with
;; the Pair: case above and resolution of types like Mu, all the
;; List: cases should be covered.
[((Value: '()) (Sequence: (list t*))) A0]
[((HeterogeneousVector: ts) (Sequence: (list t*)))
(subtypes* A0 ts (map (λ (_) t*) ts))]
[((Vector: t) (Sequence: (list t*)))

7
pkgs/typed-racket-pkgs/typed-racket-test/tests/typed-racket/succeed/pr14364.rkt Normal file
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@ -0,0 +1,7 @@
#lang typed/racket
;; A test for PR 14364. Should not infinite loop.
(struct: (X) Foo ([y : (U X (Pair (Foo X) (Foo X)))]))
(: x (Foo String))
(define x (Foo "a"))