Im getting the impl has stricter requirements than trait error (E0276) in a trait declaration, which is very confusing. just asking if anybody has encountered this before?
Without a snippet that replicates your trait and the problematic implementation, it will be hard to give you any advice on how to fix it.
use std::{
collections::BTreeMap,
fmt::{self, Formatter},
hash::Hash,
ops::Deref,
};
use derive_more::Display;
use either::Either;
use ordered_float::OrderedFloat;
/// A unique identifier for a class of nodes in the store.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Display, Hash)]
pub struct Class(u128);
impl Class {
/// Generates a new random Class identifier.
pub fn random() -> Self {
Self(uuid::Uuid::new_v4().as_u128())
}
}
/// A trait representing a store that can hold nodes of type `N` along with their analysis information of type `A`.
pub trait Store<N, A>
where
Self: Sized,
N: Node,
A: Analysis<N, Self>,
{
type Node;
/// Inserts the given node into the store, generating a new Class for it.
fn insert(&mut self, node: N) -> Class;
/// Inserts the given node along with its analysis information into the store,
/// generating a new Class for it.
fn insert_with_analysis(&mut self, node: N, analysis: A) -> Class;
/// Merges the given analysis information into the existing analysis for the specified class.
/// If the merge is successful, returns `Ok(())`. If the Class does not exist in the store, returns `Err(analysis)`.
fn merge_analysis(&mut self, class: Class, analysis: A) -> Result<(), A>;
/// Returns an iterattor over all classes in the store.
fn classes(&self) -> impl Iterator<Item = Class> + '_;
/// Returns an iterator over the nodes associated with the specified class.
/// If the class does not exist in the store, returns `None`.
fn iterate<'a>(&'a self, class: Class) -> Option<impl Iterator<Item = &'a Self::Node> + 'a>
where
<Self as Store<N, A>>::Node: 'a;
/// Extracts the most optimal node from the specified class based on the provided cost function.
/// If the class does not exist in the store or has no nodes, returns `None`.
fn extract(&self, class: Class, cost: &impl Cost<N, A, Self>) -> Option<&Self::Node> {
let nodes = self.iterate(class)?;
nodes.min_by_key(|node| cost.cost(node, self))
}
/// Returns a mutable iterator over the nodes associated with the specified class.
/// If the class does not exist in the store, returns `None`.
fn iterate_mut<'a>(
&'a mut self,
class: Class,
) -> Option<impl Iterator<Item = &'a mut Self::Node> + 'a>
where
<Self as Store<N, A>>::Node: 'a;
/// Returns the Analysis information associated with the specified class.
/// If the class does not exist in the store, returns `None`.
fn analysis(&self, class: Class) -> Option<&A>;
/// Returns a mutable reference to the Analysis information associated with the specified class.
/// If the class does not exist in the store, returns `None`.
fn analysis_mut(&mut self, class: Class) -> Option<&mut A>;
/// Searches the store using the provided searcher, returning an iterator over the search results.
/// The searcher defines how to search each node in the store.
fn search<'a, S>(&'a self, searcher: &'a S) -> impl Iterator<Item = S::Output> + 'a
where
S: Searcher<N, A, Self>,
<Self as Store<N, A>>::Node: 'a,
{
self.classes().flat_map(move |class| {
let nodes = self
.iterate(class)
.expect("Incorrect implementation of Store::classes");
nodes.filter_map(move |node| searcher.search(node, self))
})
}
/// Mutates the nodes in the store using the provided searcher and mutator function.
/// The searcher defines which nodes to mutate, and the mutator function defines how to mutate them.
/// The mutator function takes the search result and a mutable reference to the node to be mutated.
/// If the searcher finds no matching nodes, no mutation occurs.
fn mutate<S>(
&mut self,
searcher: &S,
mutator: impl for<'a> FnMut(S::Output, &'a mut Self::Node),
) where
S: Searcher<N, A, Self>;
}
pub trait TryAccess<A> {
fn try_access(&self) -> Option<&A>;
}
impl<T> TryAccess<T> for T {
fn try_access(&self) -> Option<&T> {
Some(self)
}
}
pub trait Variable<N, A, V>
where
N: Node,
A: Analysis<N, Self>,
Self: Store<N, A>,
{
/// Inserts a variable of type `V` into the store, generating a new Class for it.
fn variable(&mut self, v: V) -> Class;
/// Inserts a variable of type `V` along with its analysis information into the store,
/// generating a new Class for it.
fn variable_with_analysis(&mut self, v: V, analysis: A) -> Class;
}
pub trait Analysis<N, S>
where
Self: Sized,
N: Node,
S: Store<N, Self>,
{
/// Analyzes the given node and produces an analysis result.
fn analyze(node: &S::Node, store: &S) -> Self;
/// Merges another analysis result into this one.
fn merge(&mut self, other: Self);
}
pub trait Node: Sized {
fn children(&self) -> impl Iterator<Item = Class>;
}
pub trait Searcher<N, A, S>
where
Self: Sized,
N: Node,
A: Analysis<N, S>,
S: Store<N, A>,
{
type Output;
/// Searches the given node within the context of the provided store,
/// returning `None` if no result is found, or `Some(Output)` if a result is found.
fn search(&self, node: &S::Node, store: &S) -> Option<Self::Output>;
}
pub trait Show<A, S>
where
Self: Node,
A: Analysis<Self, S>,
S: Store<Self, A>,
{
fn show(&self, store: &S, fmt: &mut Formatter) -> fmt::Result;
fn show_analysis(&self, analysis: &A, store: &S, fmt: &mut Formatter) -> fmt::Result;
}
pub trait SExpr {
/// Produces the first expression in S-expression format for this node type.
/// Does not consider the child nodes, only the current node.
fn expression(&self) -> String;
}
pub trait Cost<N, A, S>
where
Self: Sized,
N: Node,
A: Analysis<N, S>,
S: Store<N, A>,
{
/// Computes the cost of the given node within the context of the provided store.
fn cost(&self, node: &S::Node, store: &S) -> OrderedFloat<f64>;
}
impl<N, A, S, F> Cost<N, A, S> for F
where
N: Node,
A: Analysis<N, S>,
S: Store<N, A>,
F: Fn(&<S as Store<N, A>>::Node, &S) -> OrderedFloat<f64>,
for<'a> &'a <S as Store<N, A>>::Node: Deref<Target = N>,
{
fn cost(&self, node: &<S as Store<N, A>>::Node, store: &S) -> OrderedFloat<f64> {
self(node, store)
}
}
impl<N, A, S, F, O> Searcher<N, A, S> for F
where
N: Node,
A: Analysis<N, S>,
S: Store<N, A>,
F: for<'a> Fn(&S::Node, &S) -> Option<O> + 'static,
for<'a> &'a <S as Store<N, A>>::Node: Deref<Target = N>,
{
type Output = O;
fn search(&self, node: &S::Node, store: &S) -> Option<Self::Output> {
self(node, store)
}
}
/// A recursive expression store that holds nodes of type `N` along with their analysis information of type `A`.
/// This only stores a single representation of an Expression, i.e., it does not support multiple equivalent nodes per class.
pub struct RecExpr<N, A>
where
N: Node,
A: Analysis<N, Self>,
{
main: Class,
nodes: BTreeMap<Class, (N, A)>,
}
impl<N, A> RecExpr<N, A>
where
N: Node,
A: Analysis<N, Self>,
{
pub fn build(f: impl FnOnce(&mut Self) -> N) -> Self {
let mut expr = Self {
main: Class::random(),
nodes: BTreeMap::new(),
};
let main_node = f(&mut expr);
let analysis = A::analyze(&main_node, &expr);
expr.nodes.insert(expr.main, (main_node, analysis));
expr
}
/// Displays the main node of the recursive expression using the provided formatter.
/// If the main class is invalid, this function will panic.
pub fn show(&self, fmt: &mut Formatter) -> fmt::Result
where
N: Show<A, Self>,
{
if let Some((node, _)) = self.nodes.get(&self.main) {
node.show(self, fmt)
} else {
panic!("RecExpr::show was called with an invalid main class")
}
}
/// Displays the analysis information of the main node of the recursive expression using the provided formatter.
/// If the main class is invalid, this function will panic.
pub fn show_analysis(&self, fmt: &mut Formatter) -> fmt::Result
where
N: Show<A, Self>,
{
if let Some((node, analysis)) = self.nodes.get(&self.main) {
node.show_analysis(analysis, self, fmt)
} else {
panic!("RecExpr::show_analysis was called with an invalid main class")
}
}
}
impl<N, A> Store<N, A> for RecExpr<N, A>
where
N: Node,
A: Analysis<N, Self>,
{
type Node = N;
fn insert(&mut self, node: N) -> Class {
let class = Class::random();
let analysis = A::analyze(&node, self);
self.nodes.insert(class, (node, analysis));
class
}
fn insert_with_analysis(&mut self, node: N, analysis: A) -> Class {
let class = Class::random();
self.nodes.insert(class, (node, analysis));
class
}
fn merge_analysis(&mut self, class: Class, analysis: A) -> Result<(), A> {
if let Some((_, existing_analysis)) = self.nodes.get_mut(&class) {
existing_analysis.merge(analysis);
Ok(())
} else {
Err(analysis)
}
}
fn classes(&self) -> impl Iterator<Item = Class> + '_ {
self.nodes.keys().copied()
}
fn iterate<'a>(&'a self, class: Class) -> Option<impl Iterator<Item = &'a Self::Node> + 'a>
where
<Self as Store<N, A>>::Node: 'a,
{
self.nodes
.get(&class)
.map(|(node, _)| std::iter::once(node))
}
fn iterate_mut<'a>(
&'a mut self,
class: Class,
) -> Option<impl Iterator<Item = &'a mut Self::Node> + 'a>
where
<Self as Store<N, A>>::Node: 'a,
{
self.nodes
.get_mut(&class)
.map(|(node, _)| std::iter::once(node))
}
fn analysis(&self, class: Class) -> Option<&A> {
self.nodes.get(&class).map(|(_, analysis)| analysis)
}
fn analysis_mut(&mut self, class: Class) -> Option<&mut A> {
self.nodes.get_mut(&class).map(|(_, analysis)| analysis)
}
fn mutate<S>(
&mut self,
searcher: &S,
mut mutator: impl for<'a> FnMut(S::Output, &'a mut Self::Node),
) where
S: Searcher<N, A, Self>,
{
let classes: Vec<Class> = self.classes().collect();
for class in classes {
let node = self.nodes.get(&class).expect("A class disappeared");
if let Some(search_result) = searcher.search(&node.0, self) {
let node = self.nodes.get_mut(&class).expect("A class disappeared");
mutator(search_result, &mut node.0);
}
}
}
}
/// A recursive pattern store that holds pattern nodes of type `N`
/// or variables of type `V` along with their analysis information of type `A`.
pub struct RecPattern<N, A, V> {
main: Class,
nodes: BTreeMap<Class, (Either<N, V>, A)>,
}
impl<N, A, V> Store<N, A> for RecPattern<N, A, V>
where
N: Node,
A: Analysis<N, Self>,
{
type Node = Either<N, V>;
fn insert(&mut self, node: N) -> Class {
let class = Class::random();
let node = Either::Left(node);
let analysis = A::analyze(&node, self);
self.nodes.insert(class, (node, analysis));
class
}
fn insert_with_analysis(&mut self, node: N, analysis: A) -> Class {
let class = Class::random();
let node = Either::Left(node);
self.nodes.insert(class, (node, analysis));
class
}
fn merge_analysis(&mut self, class: Class, analysis: A) -> Result<(), A> {
if let Some((_, existing_analysis)) = self.nodes.get_mut(&class) {
existing_analysis.merge(analysis);
Ok(())
} else {
Err(analysis)
}
}
fn classes(&self) -> impl Iterator<Item = Class> + '_ {
self.nodes.keys().copied()
}
fn iterate<'a>(&'a self, class: Class) -> Option<impl Iterator<Item = &'a Self::Node> + 'a>
where
<Self as Store<N, A>>::Node: 'a,
{
self.nodes
.get(&class)
.map(|(node, _)| std::iter::once(node))
}
fn iterate_mut<'a>(
&'a mut self,
class: Class,
) -> Option<impl Iterator<Item = &'a mut Self::Node> + 'a>
where
<Self as Store<N, A>>::Node: 'a,
{
self.nodes
.get_mut(&class)
.map(|(node, _)| std::iter::once(node))
}
fn analysis(&self, class: Class) -> Option<&A> {
self.nodes.get(&class).map(|(_, analysis)| analysis)
}
fn analysis_mut(&mut self, class: Class) -> Option<&mut A> {
self.nodes.get_mut(&class).map(|(_, analysis)| analysis)
}
fn mutate<S>(
&mut self,
searcher: &S,
mut mutator: impl for<'a> FnMut(S::Output, &'a mut Self::Node),
) where
S: Searcher<N, A, Self>,
{
let classes: Vec<Class> = self.classes().collect();
for class in classes {
let node = self.nodes.get(&class).expect("A class disappeared");
if let Some(search_result) = searcher.search(&node.0, self) {
let node = self.nodes.get_mut(&class).expect("A class disappeared");
mutator(search_result, &mut node.0);
}
}
}
}
commenting out the impl<N, A, V> Store<N, A> for RecPattern<N, A, V> resolves the Error. The Error output from cargo check is:
Checking kanon v0.1.0 (/Users/lukahasch/Desktop/kanon)
error[E0276]: impl has stricter requirements than trait
--> src/ctx/mod.rs:46:38
|
46 | <Self as Store<N, A>>::Node: 'a;
| ^^ impl has extra requirement `N: 'a`
error[E0276]: impl has stricter requirements than trait
--> src/ctx/mod.rs:46:38
|
46 | <Self as Store<N, A>>::Node: 'a;
| ^^ impl has extra requirement `V: 'a`
error[E0276]: impl has stricter requirements than trait
--> src/ctx/mod.rs:60:38
|
60 | <Self as Store<N, A>>::Node: 'a;
| ^^ impl has extra requirement `N: 'a`
error[E0276]: impl has stricter requirements than trait
--> src/ctx/mod.rs:60:38
|
60 | <Self as Store<N, A>>::Node: 'a;
| ^^ impl has extra requirement `V: 'a`
For more information about this error, try `rustc --explain E0276`.
error: could not compile `kanon` (lib) due to 4 previous errors
The Error messages are in the trait declaration not implementation.
The rust version is:
lukahasch@mac:~/Desktop/kanon/ > rustc --version
rustc 1.94.0-nightly (e7d44143a 2025-12-24)
lukahasch@mac:~/Desktop/kanon/ > cargo --version
cargo 1.94.0-nightly (3861f60f6 2025-12-19)
I have no minimal reproducible example just wanted to know if anybody heard of this error.
In general, this error means that the function declaration in the impl is trying to impose an additional requirement beyond that of the function declaration in the trait. You can usually fix it by changing the impl function signature to match the trait. But it looks like they are already the same here. I suspect that the compiler should actually be reporting a different problem, but I don’t know exactly what it is or how to fix it.
Perhaps someone else cleverer will come along and suggest what to do, but until then, I would suggest that you should work on minimizing the problem — delete elements and simplify things that are not strictly necessary to demonstrate it. This will help people look at your code and be able to say “aha, that problem”.
The error diagnostics are pretty bad, like not pointing at the error site.
I believe the core issue is that in this signature (and the iterate_mut version too)...
fn iterate<'a>(
&'a self,
class: Class
) -> Option<impl Iterator<Item = &'a Self::Node> + 'a>
where
<Self as Store<N, A>>::Node: 'a;
...requires everything that is (or could be) a part of <Self as Store<N, A>>::Node to meet a : 'a bound. Then in the implementation for RecPatter<N, A, V>, Node is Either<N, V>, so this means that V: 'a is required. I would think this is indirectly implied by the trait definition (see below), but for whatever reason it doesn't seem to be.
The trait doesn't have a way to mention V directly, but you can try changing the trait like so:
fn iterate<'a>(&'a self, class: Class) -> Option<impl Iterator<Item = &'a Self::Node> + 'a>
where
+ Self: 'a,
<Self as Store<N, A>>::Node: 'a;
fn iterate_mut<'a>(
&'a mut self,
class: Class,
) -> Option<impl Iterator<Item = &'a mut Self::Node> + 'a>
where
+ Self: 'a,
<Self as Store<N, A>>::Node: 'a;
This fixes the error, notionally because V is part of Self in the implementation that errors. Minimal change.
That said, I can't fully explain why this extra bound is required, as Self: 'a should be implied here due to the presence of self: &'a Self in the signature. You could consider filing an issue about that. (&'a Node is also present, as is + 'a which applies to all generic parameters, but both are within an -> impl Trait ..., and I'm less sure about the implications of that.)
I wouldn't expect the change to be breaking for similar reasons, but since I can't explain why the extra bound is required, who knows.
(You also probably don't actually need + 'a in the return type, but I'm not sure removing will do you any good either, so I stopped there.)
4 Likes
Minimization. It's not fixed by the next solver either.
Perhaps related, but also probably still worth filing an issue. If anyone does, please link it here. (If no one does, I might later.)
1 Like
thank you!!!!!!! fixed.
2 Likes