rust/tests/ui/issues/issue-67552.rs

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// build-fail
// compile-flags: -Copt-level=0
// normalize-stderr-test: ".nll/" -> "/"
mir: adjust conditional in recursion limit check This commit adjusts the condition used in the recursion limit check of the monomorphization collector, from `>` to `>=`. In #67552, the test case had infinite indirect recursion, repeating a handful of functions (from the perspective of the monomorphization collector): `rec` -> `identity` -> `Iterator::count` -> `Iterator::fold` -> `Iterator::next` -> `rec`. During this process, `resolve_associated_item` was invoked for `Iterator::fold` (during the construction of an `Instance`), and ICE'd due to substitutions needing inference. However, previous iterations of this recursion would have called this function for `Iterator::fold` - and did! - and succeeded in doing so (trivially checkable from debug logging, `()` is present where `_` is in the substs of the failing execution). The expected outcome of this test case would be a recursion limit error (which is present when the `identity` fn indirection is removed), and the recursion depth of `rec` is increasing (other functions finish collecting their neighbours and thus have their recursion depths reset). When the ICE occurs, the recursion depth of `rec` is 256 (which matches the recursion limit), which suggests perhaps that a different part of the compiler is using a `>=` comparison and returning a different result on this recursion rather than what it returned in every previous recursion, thus stopping the monomorphization collector from reporting an error on the next recursion, where `recursion_depth_of_rec > 256` would have been true. With grep and some educated guesses, we can determine that the recursion limit check at line 818 in `src/librustc_trait_selection/traits/project.rs` is the other check that is using a different comparison. Modifying either comparison to be `>` or `>=` respectively will fix the error, but changing the monomorphization collector produces the nicer error. Signed-off-by: David Wood <david@davidtw.co>
2020-05-24 10:03:11 -05:00
fn main() {
rec(Empty);
}
struct Empty;
impl Iterator for Empty {
type Item = ();
fn next<'a>(&'a mut self) -> core::option::Option<()> {
None
}
}
fn identity<T>(x: T) -> T {
x
}
fn rec<T>(mut it: T)
where
T: Iterator,
{
if () == () {
T::count(it);
} else {
rec(identity(&mut it))
//~^ ERROR reached the recursion limit while instantiating
mir: adjust conditional in recursion limit check This commit adjusts the condition used in the recursion limit check of the monomorphization collector, from `>` to `>=`. In #67552, the test case had infinite indirect recursion, repeating a handful of functions (from the perspective of the monomorphization collector): `rec` -> `identity` -> `Iterator::count` -> `Iterator::fold` -> `Iterator::next` -> `rec`. During this process, `resolve_associated_item` was invoked for `Iterator::fold` (during the construction of an `Instance`), and ICE'd due to substitutions needing inference. However, previous iterations of this recursion would have called this function for `Iterator::fold` - and did! - and succeeded in doing so (trivially checkable from debug logging, `()` is present where `_` is in the substs of the failing execution). The expected outcome of this test case would be a recursion limit error (which is present when the `identity` fn indirection is removed), and the recursion depth of `rec` is increasing (other functions finish collecting their neighbours and thus have their recursion depths reset). When the ICE occurs, the recursion depth of `rec` is 256 (which matches the recursion limit), which suggests perhaps that a different part of the compiler is using a `>=` comparison and returning a different result on this recursion rather than what it returned in every previous recursion, thus stopping the monomorphization collector from reporting an error on the next recursion, where `recursion_depth_of_rec > 256` would have been true. With grep and some educated guesses, we can determine that the recursion limit check at line 818 in `src/librustc_trait_selection/traits/project.rs` is the other check that is using a different comparison. Modifying either comparison to be `>` or `>=` respectively will fix the error, but changing the monomorphization collector produces the nicer error. Signed-off-by: David Wood <david@davidtw.co>
2020-05-24 10:03:11 -05:00
}
}