Optimize flattening of of ClassTy trees

Qualified class names are represented recursively, and need to be flattened in
several places during binding. Add a recursive method to ClassTy to do the
flattening, and avoid some garbage from using ArrayDeque and doing a copy.

PiperOrigin-RevId: 841646029

Author: cushon

java/com/google/turbine/binder/ConstEvaluator.java

@@ -61,7 +61,6 @@
 import com.google.turbine.tree.TurbineOperatorKind;
 import com.google.turbine.type.AnnoInfo;
 import com.google.turbine.type.Type;
-import java.util.ArrayDeque;
 import java.util.Iterator;
 import java.util.LinkedHashMap;
 import java.util.Map;
@@ -170,11 +169,8 @@ private Type evalClassLiteralType(Tree.Type type) {
    * isn't completed during the hierarchy phase).
    */
   private Type resolveClass(ClassTy classTy) {
-    ArrayDeque<Ident> flat = new ArrayDeque<>();
-    for (ClassTy curr = classTy; curr != null; curr = curr.base().orElse(null)) {
-      flat.addFirst(curr.name());
-    }
-    LookupResult result = scope.lookup(new LookupKey(ImmutableList.copyOf(flat)));
+    ImmutableList<Ident> flat = classTy.qualifiedName();
+    LookupResult result = scope.lookup(new LookupKey(flat));
     if (result == null) {
       log.error(classTy.position(), ErrorKind.CANNOT_RESOLVE, flat.getFirst());
       return Type.ErrorTy.create(flat, ImmutableList.of());

java/com/google/turbine/binder/HierarchyBinder.java

@@ -33,7 +33,6 @@
 import com.google.turbine.model.TurbineTyKind;
 import com.google.turbine.tree.Tree;
 import com.google.turbine.tree.Tree.ClassTy;
-import java.util.ArrayDeque;
 import java.util.LinkedHashMap;
 import org.jspecify.annotations.Nullable;
 
@@ -122,12 +121,9 @@ private SourceHeaderBoundClass bind() {
   private @Nullable ClassSymbol resolveClass(Tree.ClassTy ty) {
     // flatten a left-recursive qualified type name to its component simple names
     // e.g. Foo<Bar>.Baz -> ["Foo", "Bar"]
-    ArrayDeque<Tree.Ident> flat = new ArrayDeque<>();
-    for (Tree.ClassTy curr = ty; curr != null; curr = curr.base().orElse(null)) {
-      flat.addFirst(curr.name());
-    }
+    ImmutableList<Tree.Ident> flat = ty.qualifiedName();
     // Resolve the base symbol in the qualified name.
-    LookupResult result = lookup(ty, new LookupKey(ImmutableList.copyOf(flat)));
+    LookupResult result = lookup(ty, new LookupKey(flat));
     if (result == null) {
       log.error(ty.position(), ErrorKind.CANNOT_RESOLVE, Joiner.on('.').join(flat));
       return null;

java/com/google/turbine/binder/TypeBinder.java

@@ -60,7 +60,6 @@
 import com.google.turbine.type.Type;
 import com.google.turbine.type.Type.IntersectionTy;
 import com.google.turbine.types.Deannotate;
-import java.util.ArrayDeque;
 import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.LinkedHashMap;
@@ -942,14 +941,7 @@ private Type bindTy(CompoundScope scope, Tree t) {
 
   private Type bindClassTy(CompoundScope scope, Tree.ClassTy t) {
     // flatten the components of a qualified class type
-    ArrayList<Tree.ClassTy> flat;
-    {
-      ArrayDeque<Tree.ClassTy> builder = new ArrayDeque<>();
-      for (Tree.ClassTy curr = t; curr != null; curr = curr.base().orElse(null)) {
-        builder.addFirst(curr);
-      }
-      flat = new ArrayList<>(builder);
-    }
+    ImmutableList<Tree.ClassTy> flat = t.flatten();
     // the simple names of all classes in the qualified name
     ImmutableList.Builder<Tree.Ident> nameBuilder = ImmutableList.builder();
     for (Tree.ClassTy curr : flat) {
@@ -982,7 +974,7 @@ private Type bindClassTy(CompoundScope scope, Tree.ClassTy t) {
 
   private Type bindClassTyRest(
       CompoundScope scope,
-      ArrayList<ClassTy> flat,
+      ImmutableList<ClassTy> flat,
       ImmutableList<Tree.Ident> bits,
       LookupResult result,
       ClassSymbol sym,

java/com/google/turbine/tree/Tree.java

@@ -307,6 +307,32 @@ public Ident name() {
     public ImmutableList<Type> tyargs() {
       return tyargs;
     }
+
+    public ImmutableList<ClassTy> flatten() {
+      ImmutableList.Builder<ClassTy> builder = ImmutableList.builder();
+      flatten(builder);
+      return builder.build();
+    }
+
+    private void flatten(ImmutableList.Builder<ClassTy> builder) {
+      if (base.isPresent()) {
+        base.get().flatten(builder);
+      }
+      builder.add(this);
+    }
+
+    public ImmutableList<Ident> qualifiedName() {
+      ImmutableList.Builder<Ident> builder = ImmutableList.builder();
+      qualifiedName(builder);
+      return builder.build();
+    }
+
+    private void qualifiedName(ImmutableList.Builder<Ident> builder) {
+      if (base.isPresent()) {
+        base.get().qualifiedName(builder);
+      }
+      builder.add(name());
+    }
   }
 
   /** A JLS 3.10 literal expression. */