Regression in type parameter defaults in types and impls #30123
Description
This regression is only visible in cross-crate code; NOTE it's very likely it's due to an actual rustc bug fix.
Here is some playpen code for illustration anyway.
Given a struct with default parameters and two constructor functions:
pub struct Graph<N, E, Ty = Directed, Ix: IndexType = DefIndex> {
nodes: Vec<Node<N, Ix>>,
edges: Vec<Edge<E, Ix>>,
ty: PhantomData<Ty>,
}
impl<N, E> Graph<N, E, Directed> {
pub fn new() -> Self {
Graph{nodes: Vec::new(), edges: Vec::new(), ty: PhantomData}
}
}
impl<N, E> Graph<N, E, Undirected> {
pub fn new_undirected() -> Self {
Graph{nodes: Vec::new(), edges: Vec::new(), ty: PhantomData}
}
}In Rust 1.4 or later (current stable and current nightly), both must be called like this to compile:
let g = Graph::<i32, i32>::new();
let ug = Graph::<i32, i32, _>::new_undirected();In current stable Rust 1.4, the following compiles if you import Graph across crates!
let ug = Graph::<i32, i32>::new_undirected();This is invalid in current nightly Rust ~1.6, see travis build example; the testcases are in their own crates.
tests/ograph.rs:1018:18: 1018:48 error: no associated item named `new_undirected` found for type `petgraph::graph::Graph<_, ()>` in the current scope
tests/ograph.rs:1018 let mut gr = Graph::<_, ()>::new_undirected();
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~