Fix non-deterministic proc-macro output by replacing HashSet with IndexSet (#488)

Author: capickett

Cargo.lock

@@ -16,6 +16,7 @@ no-serde-warnings = []
 proc-macro = true
 
 [dependencies]
+indexmap = "2"
 proc-macro2 = "1"
 quote = "1"
 syn = { version = "2.0.28", features = ["full", "extra-traits"] }

macros/Cargo.toml

@@ -1,13 +1,15 @@
-use std::{collections::HashSet, rc::Rc};
+use std::rc::Rc;
+
+use indexmap::IndexSet;
 
 use proc_macro2::TokenStream;
 use quote::{quote, ToTokens};
 use syn::{Path, Type};
 
 pub struct Dependencies {
     crate_rename: Rc<Path>,
-    dependencies: HashSet<Dependency>,
-    types: HashSet<Rc<Type>>,
+    dependencies: IndexSet<Dependency>,
+    types: IndexSet<Rc<Type>>,
 }
 
 #[derive(Hash, Eq, PartialEq)]
@@ -30,9 +32,9 @@ enum Dependency {
 impl Dependencies {
     pub fn new(crate_rename: Path) -> Self {
         Self {
-            dependencies: HashSet::new(),
+            dependencies: IndexSet::new(),
             crate_rename: Rc::new(crate_rename),
-            types: HashSet::new(),
+            types: IndexSet::new(),
         }
     }
 

macros/src/deps.rs

@@ -1,7 +1,9 @@
 #![macro_use]
 #![deny(unused)]
 
-use std::collections::{HashMap, HashSet};
+use std::collections::HashMap;
+
+use indexmap::IndexSet;
 
 use proc_macro2::{Ident, TokenStream};
 use quote::{format_ident, quote};
@@ -442,7 +444,7 @@ fn generate_where_clause(
     let used_types = {
         let is_type_param = |id: &Ident| generics.type_params().any(|p| &p.ident == id);
 
-        let mut used_types = HashSet::new();
+        let mut used_types = IndexSet::new();
         for ty in dependencies.used_types() {
             used_type_params(&mut used_types, ty, is_type_param);
         }
@@ -459,7 +461,7 @@ fn generate_where_clause(
 // Associated types of a type parameter are extracted as well.
 // Note: This will not extract `I` from `I::Item`, but just `I::Item`!
 fn used_type_params<'ty, 'out>(
-    out: &'out mut HashSet<&'ty Type>,
+    out: &'out mut IndexSet<&'ty Type>,
     ty: &'ty Type,
     is_type_param: impl Fn(&'ty Ident) -> bool + Copy + 'out,
 ) {