Description
I just stumbled across a weird and inconsistent behaviour, that seems unreasonable to me.
The project I'm working on is a big company project (closed source) with quite some files. While fixing a bug and editing one line in one module (src/dispatcher/compiler/module_range.rs) the compiler suddenly decided to reject the code of a function from a completely different module (src/services/module_state_service.rs) that has absolutely nothing to do with the module I'm working on.
The change that I made:
fn get_next_module_start(&self, module: &FunctionalModule<'a>, starter: &'a Fmid) -> Result<usize> {
// -- snip --
WorkflowIterator::exe_path_iter(
self.modules,
starter,
|m| m.fmd.next_module.as_ref().into_option(),
- |m| super::sort_exe_paths(&m.fmd.exe_paths),
+ |m| (m != module).then(|| super::sort_exe_paths(&m.fmd.exe_paths)).into_iter().flatten(),
|m| m.md.kind,
)
// -- snip --
}The compiler error:
error: lifetime may not live long enough
--> src/services/module_state_service.rs:35:44
|
32 | &'_ self,
| -- let's call the lifetime of this reference `'1`
33 | workflow_id: &WorkflowGroupId,
34 | fmid: &Fmid,
| - let's call the lifetime of this reference `'2`
35 | ) -> Option<RwLockReadGuard<'_, [u8]>> {
| ____________________________________________^
36 | | let map_guard = self.module_state.read().await;
37 | |
38 | | let contains_state = map_guard
... |
49 | | }))
50 | | }
| |_____^ associated function was supposed to return data with lifetime `'1` but it is returning data with lifetime `'2`
error: lifetime may not live long enough
--> src/services/module_state_service.rs:47:9
|
32 | &'_ self,
| -- let's call the lifetime of this reference `'1`
33 | workflow_id: &WorkflowGroupId,
34 | fmid: &Fmid,
| - let's call the lifetime of this reference `'2`
...
47 | / Some(RwLockReadGuard::map(map_guard, |map| {
48 | | &**map.get(workflow_id).unwrap().get(fmid).unwrap()
49 | | }))
| |___________^ associated function was supposed to return data with lifetime `'2` but it is returning data with lifetime `'1`
The function the compiler complains about:
pub async fn get_module_state(
&'_ self,
workflow_id: &WorkflowGroupId,
fmid: &Fmid,
) -> Option<RwLockReadGuard<'_, [u8]>> {
let map_guard = self.module_state.read().await;
let contains_state = map_guard
.get(workflow_id)
.map(|map| map.contains_key(fmid))
.unwrap_or_default();
if !contains_state {
return None;
}
Some(RwLockReadGuard::map(map_guard, |map| {
&**map.get(workflow_id).unwrap().get(fmid).unwrap()
}))
}When undoing the one-line change, the code compiled fine again, and after redoing it, it failed to compile again.
Now, after indenting a few pieces of code, to make pasting them into GitHub easier, the compiler again accepts the code.
I'm also no longer able to recreate the error.
I know, that's essentially nothing to work with, and I'm not even able to recreate the issue myself anymore, but it seems worth reporting to me.