Move OnceMap into its own crate (#946)

## Summary

This is extremely generic (like `WaitMap`), and I want to use it in the
cache.

Cargo.lock

@@ -1922,6 +1922,14 @@ dependencies = [
  "memchr",
 ]
 
+[[package]]
+name = "once-map"
+version = "0.0.1"
+dependencies = [
+ "rustc-hash",
+ "waitmap",
+]
+
 [[package]]
 name = "once_cell"
 version = "1.19.0"
@@ -2680,6 +2688,7 @@ dependencies = [
  "insta",
  "install-wheel-rs",
  "itertools 0.12.0",
+ "once-map",
  "once_cell",
  "owo-colors",
  "pep440_rs 0.3.12",
@@ -2718,12 +2727,11 @@ version = "0.0.1"
 dependencies = [
  "anyhow",
  "distribution-types",
+ "once-map",
  "pep508_rs",
  "puffin-cache",
  "puffin-interpreter",
- "rustc-hash",
  "tokio",
- "waitmap",
 ]
 
 [[package]]

crates/README.md

@@ -26,6 +26,11 @@ A `venv` replacement to create virtual environments in Rust.
 
 Install built distributions (wheels) into a virtual environment.]
 
+## [once-map](./once-map)
+
+A [`waitmap`](https://github.com/withoutboats/waitmap)-like concurrent hash map for executing tasks
+exactly once.
+
 ## [pep440-rs](./pep440-rs)
 
 Utilities for interacting with Python version numbers and specifiers.

crates/once-map/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "once-map"
+version = "0.0.1"
+edition = { workspace = true }
+rust-version = { workspace = true }
+homepage = { workspace = true }
+documentation = { workspace = true }
+repository = { workspace = true }
+authors = { workspace = true }
+license = { workspace = true }
+
+[lints]
+workspace = true
+
+[dependencies]
+rustc-hash = { workspace = true }
+waitmap = { workspace = true }

crates/puffin-resolver/Cargo.toml

@@ -17,6 +17,7 @@ cache-key = { path = "../cache-key" }
 distribution-filename = { path = "../distribution-filename", features = ["serde"] }
 distribution-types = { path = "../distribution-types" }
 install-wheel-rs = { path = "../install-wheel-rs" }
+once-map = { path = "../once-map" }
 pep440_rs = { path = "../pep440-rs", features = ["pubgrub"] }
 pep508_rs = { path = "../pep508-rs" }
 platform-host = { path = "../platform-host" }
@@ -26,9 +27,9 @@ puffin-client = { path = "../puffin-client" }
 puffin-distribution = { path = "../puffin-distribution" }
 puffin-git = { path = "../puffin-git" }
 puffin-interpreter = { path = "../puffin-interpreter" }
-puffin-warnings = { path = "../puffin-warnings" }
 puffin-normalize = { path = "../puffin-normalize" }
 puffin-traits = { path = "../puffin-traits" }
+puffin-warnings = { path = "../puffin-warnings" }
 pypi-types = { path = "../pypi-types" }
 requirements-txt = { path = "../requirements-txt" }
 

crates/puffin-resolver/src/error.rs

@@ -8,11 +8,11 @@ use thiserror::Error;
 use url::Url;
 
 use distribution_types::{BuiltDist, PathBuiltDist, PathSourceDist, SourceDist};
+use once_map::OnceMap;
 use pep440_rs::Version;
 use pep508_rs::Requirement;
 use puffin_distribution::DistributionDatabaseError;
 use puffin_normalize::PackageName;
-use puffin_traits::OnceMap;
 
 use crate::candidate_selector::CandidateSelector;
 use crate::pubgrub::{PubGrubPackage, PubGrubPython, PubGrubReportFormatter};

crates/puffin-resolver/src/resolution.rs

@@ -12,10 +12,10 @@ use rustc_hash::FxHashMap;
 use url::Url;
 
 use distribution_types::{Dist, DistributionMetadata, LocalEditable, Name, PackageId, Verbatim};
+use once_map::OnceMap;
 use pep440_rs::Version;
 use pep508_rs::VerbatimUrl;
 use puffin_normalize::{ExtraName, PackageName};
-use puffin_traits::OnceMap;
 use pypi_types::{Hashes, Metadata21};
 
 use crate::pins::FilePins;

crates/puffin-resolver/src/resolver/index.rs

@@ -2,8 +2,8 @@ use dashmap::DashMap;
 use url::Url;
 
 use distribution_types::PackageId;
+use once_map::OnceMap;
 use puffin_normalize::PackageName;
-use puffin_traits::OnceMap;
 use pypi_types::Metadata21;
 
 use crate::version_map::VersionMap;

crates/puffin-traits/Cargo.toml

@@ -14,11 +14,10 @@ workspace = true
 
 [dependencies]
 distribution-types = { path = "../distribution-types" }
+once-map = { path = "../once-map" }
 pep508_rs = { path = "../pep508-rs" }
 puffin-cache = { path = "../puffin-cache" }
 puffin-interpreter = { path = "../puffin-interpreter" }
 
 anyhow = { workspace = true }
-rustc-hash = { workspace = true }
 tokio = { workspace = true, features = ["sync"] }
-waitmap = { workspace = true }

crates/puffin-traits/src/lib.rs

@@ -7,13 +7,11 @@ use std::path::{Path, PathBuf};
 use anyhow::Result;
 
 use distribution_types::{CachedDist, DistributionId, Resolution};
-pub use once_map::OnceMap;
+use once_map::OnceMap;
 use pep508_rs::Requirement;
 use puffin_cache::Cache;
 use puffin_interpreter::{Interpreter, Virtualenv};
 
-mod once_map;
-
 /// Avoid cyclic crate dependencies between resolver, installer and builder.
 ///
 /// To resolve the dependencies of a packages, we may need to build one or more source