Gradualizer may fall into infinite loop for recursive types. #322
Comments
ilya-klyuchnikov
changed the title
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very nice minimal example |
Given a recursive type, typechecker:normalize() can recurse forever if we don't take care to stop the recursion. This patch adds a set to keep track of the types that `normalize` has unfolded so far and stops unfolding if asked to normalize a type that has already been unfolded. Ilya identified the problem with recursives types in #322 and offered a nice example program to demonstrate the problem. Fixes #322 although the program is still not accepted as it should be so I'm adding it to the known problems.
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Not sure if a similar example has been covered already, but I'm seeing an infinite loop with the following code: -module(sample).
-compile([export_all]).
-type t() :: t().
-spec main() -> t().
main() -> ok.tested with |
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@mheiber thanks for this example. I think it's a different issue. Types can refer to itself inside a tuple etc. but it's not allowed to be recursive on the top level, so we should detect it and give an error for this. |
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Separate please (unless you think it will be solved by the same fix??) |
I think both issues have to do with checking subtype or type equivalence for recursive types–I suspect they will have a common solution. |
Given a recursive type, typechecker:normalize() can recurse forever if we don't take care to stop the recursion. This patch adds a set to keep track of the types that `normalize` has unfolded so far and stops unfolding if asked to normalize a type that has already been unfolded. Ilya identified the problem with recursives types in josefs#322 and offered a nice example program to demonstrate the problem. Fixes josefs#322 although the program is still not accepted as it should be so I'm adding it to the known problems.
Given a recursive type, typechecker:normalize() can recurse forever if we don't take care to stop the recursion. This patch adds a set to keep track of the types that `normalize` has unfolded so far and stops unfolding if asked to normalize a type that has already been unfolded. Ilya identified the problem with recursives types in josefs#322 and offered a nice example program to demonstrate the problem. Fixes josefs#322 although the program is still not accepted as it should be so I'm adding it to the known problems.
Given a recursive type, typechecker:normalize() can recurse forever if we don't take care to stop the recursion. This patch adds a set to keep track of the types that `normalize` has unfolded so far and stops unfolding if asked to normalize a type that has already been unfolded. Ilya identified the problem with recursives types in josefs#322 and offered a nice example program to demonstrate the problem. Fixes josefs#322 although the program is still not accepted as it should be so I'm adding it to the known problems.
A repro:
This goes into loop:
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