From 48ebae9cef6fdb1af495e692a0811634f308e447 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?R=C3=A9my=20Rakic?= Date: Thu, 26 Jun 2025 15:27:23 +0000 Subject: [PATCH] add NLL-like imprecision example This test showcases the same imprecision as NLLs, unlike the datalog implementation, when using reachability as a liveness approximation. --- .../flow-sensitive-invariance.nll.stderr | 36 +++++++++++++++++++ .../flow-sensitive-invariance.polonius.stderr | 36 +++++++++++++++++++ .../nll/polonius/flow-sensitive-invariance.rs | 34 ++++++++++++++++++ 3 files changed, 106 insertions(+) create mode 100644 tests/ui/nll/polonius/flow-sensitive-invariance.nll.stderr create mode 100644 tests/ui/nll/polonius/flow-sensitive-invariance.polonius.stderr create mode 100644 tests/ui/nll/polonius/flow-sensitive-invariance.rs diff --git a/tests/ui/nll/polonius/flow-sensitive-invariance.nll.stderr b/tests/ui/nll/polonius/flow-sensitive-invariance.nll.stderr new file mode 100644 index 000000000000..5756148f4eb2 --- /dev/null +++ b/tests/ui/nll/polonius/flow-sensitive-invariance.nll.stderr @@ -0,0 +1,36 @@ +error: lifetime may not live long enough + --> $DIR/flow-sensitive-invariance.rs:20:17 + | +LL | fn use_it<'a, 'b>(choice: bool) -> Result, Invariant<'b>> { + | -- -- lifetime `'b` defined here + | | + | lifetime `'a` defined here +LL | let returned_value = create_invariant(); +LL | if choice { Ok(returned_value) } else { Err(returned_value) } + | ^^^^^^^^^^^^^^^^^^ function was supposed to return data with lifetime `'a` but it is returning data with lifetime `'b` + | + = help: consider adding the following bound: `'b: 'a` + = note: requirement occurs because of the type `Invariant<'_>`, which makes the generic argument `'_` invariant + = note: the struct `Invariant<'l>` is invariant over the parameter `'l` + = help: see for more information about variance + +error: lifetime may not live long enough + --> $DIR/flow-sensitive-invariance.rs:20:45 + | +LL | fn use_it<'a, 'b>(choice: bool) -> Result, Invariant<'b>> { + | -- -- lifetime `'b` defined here + | | + | lifetime `'a` defined here +LL | let returned_value = create_invariant(); +LL | if choice { Ok(returned_value) } else { Err(returned_value) } + | ^^^^^^^^^^^^^^^^^^^ function was supposed to return data with lifetime `'b` but it is returning data with lifetime `'a` + | + = help: consider adding the following bound: `'a: 'b` + = note: requirement occurs because of the type `Invariant<'_>`, which makes the generic argument `'_` invariant + = note: the struct `Invariant<'l>` is invariant over the parameter `'l` + = help: see for more information about variance + +help: `'a` and `'b` must be the same: replace one with the other + +error: aborting due to 2 previous errors + diff --git a/tests/ui/nll/polonius/flow-sensitive-invariance.polonius.stderr b/tests/ui/nll/polonius/flow-sensitive-invariance.polonius.stderr new file mode 100644 index 000000000000..5756148f4eb2 --- /dev/null +++ b/tests/ui/nll/polonius/flow-sensitive-invariance.polonius.stderr @@ -0,0 +1,36 @@ +error: lifetime may not live long enough + --> $DIR/flow-sensitive-invariance.rs:20:17 + | +LL | fn use_it<'a, 'b>(choice: bool) -> Result, Invariant<'b>> { + | -- -- lifetime `'b` defined here + | | + | lifetime `'a` defined here +LL | let returned_value = create_invariant(); +LL | if choice { Ok(returned_value) } else { Err(returned_value) } + | ^^^^^^^^^^^^^^^^^^ function was supposed to return data with lifetime `'a` but it is returning data with lifetime `'b` + | + = help: consider adding the following bound: `'b: 'a` + = note: requirement occurs because of the type `Invariant<'_>`, which makes the generic argument `'_` invariant + = note: the struct `Invariant<'l>` is invariant over the parameter `'l` + = help: see for more information about variance + +error: lifetime may not live long enough + --> $DIR/flow-sensitive-invariance.rs:20:45 + | +LL | fn use_it<'a, 'b>(choice: bool) -> Result, Invariant<'b>> { + | -- -- lifetime `'b` defined here + | | + | lifetime `'a` defined here +LL | let returned_value = create_invariant(); +LL | if choice { Ok(returned_value) } else { Err(returned_value) } + | ^^^^^^^^^^^^^^^^^^^ function was supposed to return data with lifetime `'b` but it is returning data with lifetime `'a` + | + = help: consider adding the following bound: `'a: 'b` + = note: requirement occurs because of the type `Invariant<'_>`, which makes the generic argument `'_` invariant + = note: the struct `Invariant<'l>` is invariant over the parameter `'l` + = help: see for more information about variance + +help: `'a` and `'b` must be the same: replace one with the other + +error: aborting due to 2 previous errors + diff --git a/tests/ui/nll/polonius/flow-sensitive-invariance.rs b/tests/ui/nll/polonius/flow-sensitive-invariance.rs new file mode 100644 index 000000000000..c5571f131da3 --- /dev/null +++ b/tests/ui/nll/polonius/flow-sensitive-invariance.rs @@ -0,0 +1,34 @@ +// An example (from @steffahn) of reachability as an approximation of liveness where the polonius +// alpha analysis shows the same imprecision as NLLs, unlike the datalog implementation. + +//@ ignore-compare-mode-polonius (explicit revisions) +//@ revisions: nll polonius legacy +//@ [polonius] compile-flags: -Z polonius=next +//@ [legacy] check-pass +//@ [legacy] compile-flags: -Z polonius=legacy + +use std::cell::Cell; + +struct Invariant<'l>(Cell<&'l ()>); + +fn create_invariant<'l>() -> Invariant<'l> { + Invariant(Cell::new(&())) +} + +fn use_it<'a, 'b>(choice: bool) -> Result, Invariant<'b>> { + let returned_value = create_invariant(); + if choice { Ok(returned_value) } else { Err(returned_value) } + //[nll]~^ ERROR lifetime may not live long enough + //[nll]~| ERROR lifetime may not live long enough + //[polonius]~^^^ ERROR lifetime may not live long enough + //[polonius]~| ERROR lifetime may not live long enough +} + +fn use_it_but_its_the_same_region<'a: 'b, 'b: 'a>( + choice: bool, +) -> Result, Invariant<'b>> { + let returned_value = create_invariant(); + if choice { Ok(returned_value) } else { Err(returned_value) } +} + +fn main() {}