Reuse indexmap crate instead of manually implementing OrderedMap.

This change seems desirable, because:

* It allows dropping the `K: Copy` constraint.  (This may be needed
  to unblock future, work-in-progress commits that may require
  dropping this impl/derive from `NamedImplKey`.)
* It reduced the amount of code that has to be maintained within
  the `cxx` crates.

I note that MSRV of `indexmap` is 1.63.0 [1] which is lower than MSRV
of 1.73.0 advertised by the `cxx` crate [2].

[1] https://github.com/indexmap-rs/indexmap/blob/main/RELEASES.md#201-2023-09-27
[2] https://github.com/dtolnay/cxx/blob/b5b259f2517a003e4c05bb91cd2b346c6ee1c517/README.md?plain=1#L27-L28

Author: anforowicz

BUCK

@@ -33,6 +33,7 @@ rust_binary(
     deps = [
         "//third-party:clap",
         "//third-party:codespan-reporting",
+        "//third-party:indexmap",
         "//third-party:proc-macro2",
         "//third-party:quote",
         "//third-party:syn",
@@ -57,6 +58,7 @@ rust_library(
     edition = "2021",
     proc_macro = True,
     deps = [
+        "//third-party:indexmap",
         "//third-party:proc-macro2",
         "//third-party:quote",
         "//third-party:rustversion",
@@ -75,6 +77,7 @@ rust_library(
     deps = [
         "//third-party:cc",
         "//third-party:codespan-reporting",
+        "//third-party:indexmap",
         "//third-party:proc-macro2",
         "//third-party:quote",
         "//third-party:scratch",
@@ -93,6 +96,7 @@ rust_library(
     deps = [
         "//third-party:cc",
         "//third-party:codespan-reporting",
+        "//third-party:indexmap",
         "//third-party:proc-macro2",
         "//third-party:quote",
         "//third-party:syn",

BUILD.bazel

@@ -33,6 +33,7 @@ rust_binary(
     deps = [
         "@crates.io//:clap",
         "@crates.io//:codespan-reporting",
+        "@crates.io//:indexmap",
         "@crates.io//:proc-macro2",
         "@crates.io//:quote",
         "@crates.io//:syn",
@@ -62,6 +63,7 @@ rust_proc_macro(
         "@crates.io//:rustversion",
     ],
     deps = [
+        "@crates.io//:indexmap",
         "@crates.io//:proc-macro2",
         "@crates.io//:quote",
         "@crates.io//:syn",
@@ -76,6 +78,7 @@ rust_library(
     deps = [
         "@crates.io//:cc",
         "@crates.io//:codespan-reporting",
+        "@crates.io//:indexmap",
         "@crates.io//:proc-macro2",
         "@crates.io//:quote",
         "@crates.io//:scratch",
@@ -92,6 +95,7 @@ rust_library(
     deps = [
         "@crates.io//:cc",
         "@crates.io//:codespan-reporting",
+        "@crates.io//:indexmap",
         "@crates.io//:proc-macro2",
         "@crates.io//:quote",
         "@crates.io//:syn",

MODULE.bazel.lock

@@ -21,6 +21,7 @@ experimental-async-fn = []
 [dependencies]
 cc = "1.0.83"
 codespan-reporting = "0.12"
+indexmap = "2.9.0"
 proc-macro2 = { version = "1.0.74", default-features = false, features = ["span-locations"] }
 quote = { version = "1.0.35", default-features = false }
 scratch = "1.0.5"

gen/build/Cargo.toml

@@ -23,6 +23,7 @@ experimental-async-fn = []
 [dependencies]
 clap = { version = "4.3.11", default-features = false, features = ["error-context", "help", "std", "suggestions", "usage"] }
 codespan-reporting = "0.12"
+indexmap = "2.9.0"
 proc-macro2 = { version = "1.0.74", default-features = false, features = ["span-locations"] }
 quote = { version = "1.0.35", default-features = false }
 syn = { version = "2.0.46", default-features = false, features = ["clone-impls", "full", "parsing", "printing"] }

gen/cmd/Cargo.toml

@@ -14,6 +14,7 @@ rust-version = "1.73"
 
 [dependencies]
 codespan-reporting = "0.12"
+indexmap = "2.9.0"
 proc-macro2 = { version = "1.0.74", default-features = false, features = ["span-locations"] }
 quote = { version = "1.0.35", default-features = false }
 syn = { version = "2.0.46", default-features = false, features = ["clone-impls", "full", "parsing", "printing"] }

gen/lib/Cargo.toml

@@ -21,6 +21,7 @@ experimental-async-fn = []
 experimental-enum-variants-from-header = ["clang-ast", "flate2", "memmap", "serde", "serde_derive", "serde_json"]
 
 [dependencies]
+indexmap = "2.9.0"
 proc-macro2 = "1.0.74"
 quote = "1.0.35"
 rustversion = "1"

macro/Cargo.toml

@@ -1,73 +1,48 @@
 use std::borrow::Borrow;
 use std::hash::Hash;
 use std::ops::Index;
-use std::slice;
 
 pub(crate) use self::ordered::OrderedMap;
 pub(crate) use self::unordered::UnorderedMap;
 pub(crate) use std::collections::hash_map::Entry;
 
 mod ordered {
-    use super::{Entry, Iter, UnorderedMap};
-    use std::borrow::Borrow;
     use std::hash::Hash;
-    use std::mem;
 
-    pub(crate) struct OrderedMap<K, V> {
-        map: UnorderedMap<K, usize>,
-        vec: Vec<(K, V)>,
-    }
+    pub(crate) struct OrderedMap<K, V>(indexmap::IndexMap<K, V>);
 
     impl<K, V> OrderedMap<K, V> {
         pub(crate) fn new() -> Self {
-            OrderedMap {
-                map: UnorderedMap::new(),
-                vec: Vec::new(),
-            }
-        }
-
-        pub(crate) fn iter(&self) -> Iter<K, V> {
-            Iter(self.vec.iter())
+            OrderedMap(indexmap::IndexMap::new())
         }
 
         #[allow(dead_code)] // only used by cxx-build, not cxxbridge-macro
         pub(crate) fn keys(&self) -> impl Iterator<Item = &K> {
-            self.vec.iter().map(|(k, _v)| k)
+            self.0.keys()
         }
     }
 
     impl<K, V> OrderedMap<K, V>
     where
-        K: Copy + Hash + Eq,
+        K: Hash + Eq,
     {
         pub(crate) fn insert(&mut self, key: K, value: V) -> Option<V> {
-            match self.map.entry(key) {
-                Entry::Occupied(entry) => {
-                    let i = &mut self.vec[*entry.get()];
-                    Some(mem::replace(&mut i.1, value))
-                }
-                Entry::Vacant(entry) => {
-                    entry.insert(self.vec.len());
-                    self.vec.push((key, value));
-                    None
-                }
-            }
+            self.0.insert(key, value)
         }
 
         pub(crate) fn contains_key<Q>(&self, key: &Q) -> bool
         where
-            K: Borrow<Q>,
-            Q: ?Sized + Hash + Eq,
+            Q: ?Sized + Hash + indexmap::Equivalent<K>,
         {
-            self.map.contains_key(key)
+            self.0.contains_key(key)
         }
     }
 
     impl<'a, K, V> IntoIterator for &'a OrderedMap<K, V> {
         type Item = (&'a K, &'a V);
-        type IntoIter = Iter<'a, K, V>;
+        type IntoIter = indexmap::map::Iter<'a, K, V>;
         fn into_iter(self) -> Self::IntoIter {
-            self.iter()
+            self.0.iter()
         }
     }
 }
@@ -138,21 +113,6 @@ mod unordered {
     }
 }
 
-pub(crate) struct Iter<'a, K, V>(slice::Iter<'a, (K, V)>);
-
-impl<'a, K, V> Iterator for Iter<'a, K, V> {
-    type Item = (&'a K, &'a V);
-
-    fn next(&mut self) -> Option<Self::Item> {
-        let (k, v) = self.0.next()?;
-        Some((k, v))
-    }
-
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        self.0.size_hint()
-    }
-}
-
 impl<K, V> Default for UnorderedMap<K, V> {
     fn default() -> Self {
         UnorderedMap::new()