Ruby: use IndexMap

This is the same idea as Java's LinkedHashMap: it gives the same O(1)
insertion and lookup as HashMap, but preserves insertion order for
iteration.

ruby/extractor/Cargo.toml

@@ -18,3 +18,4 @@ tracing-subscriber = { version = "0.2", features = ["env-filter"] }
 rayon = "1.5.0"
 num_cpus = "1.13.0"
 regex = "1.4.3"
+indexmap = "1.7.0"

ruby/extractor/src/extractor.rs

@@ -1,6 +1,6 @@
 use crate::trap;
+use indexmap::IndexMap;
 use node_types::{EntryKind, Field, NodeTypeMap, Storage, TypeName};
-use std::collections::BTreeMap as Map;
 use std::fmt;
 use std::path::Path;
 
@@ -407,7 +407,7 @@ impl<'a> Visitor<'a> {
         child_nodes: &[ChildNode],
         parent_id: trap::Label,
     ) -> Option<Vec<trap::Arg>> {
-        let mut map: Map<&Option<String>, (&Field, Vec<trap::Arg>)> = Map::new();
+        let mut map: IndexMap<&Option<String>, (&Field, Vec<trap::Arg>)> = IndexMap::new();
         for field in fields {
             map.insert(&field.name, (field, Vec::new()));
         }

ruby/extractor/src/trap.rs

@@ -1,22 +1,22 @@
 use std::borrow::Cow;
-use std::collections::BTreeMap;
 use std::fmt;
 use std::io::BufWriter;
 use std::path::Path;
 
 use flate2::write::GzEncoder;
+use indexmap::IndexMap;
 
 pub struct Writer {
     /// Labels that should be assigned fresh ids, e.g. `#123=*`.
     fresh_ids: Vec<Label>,
 
     /// Labels that should be assigned trap keys, e.g. `#7=@"foo"`.
-    global_keys: BTreeMap<String, Label>,
+    global_keys: IndexMap<String, Label>,
 
     /// Database rows to emit. Each key is the tuple name, each value is a list.
     /// Each member of *that* list represents an instance of that tuple,
     /// containing a list of the arguments/column values.
-    tuples: BTreeMap<String, Vec<Vec<Arg>>>,
+    tuples: IndexMap<String, Vec<Vec<Arg>>>,
 
     /// A counter for generating fresh labels
     counter: u32,
@@ -26,8 +26,8 @@ impl Writer {
     pub fn new() -> Writer {
         Writer {
             fresh_ids: Vec::new(),
-            tuples: BTreeMap::new(),
-            global_keys: BTreeMap::new(),
+            tuples: IndexMap::new(),
+            global_keys: IndexMap::new(),
             counter: 0,
         }
     }