Reverting #12405 Compiler: don't always use Array for node dependencies and observers

src/compiler/crystal/codegen/call.cr

@@ -7,7 +7,7 @@ class Crystal::CodeGenVisitor
     end
 
     target_defs = node.target_defs
-    if target_defs.empty?
+    unless target_defs
       node.raise "BUG: no target defs"
     end
 
@@ -394,7 +394,7 @@ class Crystal::CodeGenVisitor
           position_at_end current_def_label
 
           # Prepare this specific call
-          call.target_defs = ZeroOneOrMany.new(a_def)
+          call.target_defs = [a_def] of Def
           call.obj.try &.set_type(a_def.owner)
           call.args.zip(a_def.args) do |call_arg, a_def_arg|
             call_arg.set_type(a_def_arg.type)

src/compiler/crystal/interpreter/compiler.cr

@@ -1802,7 +1802,7 @@ class Crystal::Repl::Compiler < Crystal::Visitor
     end
 
     target_defs = node.target_defs
-    if target_defs.empty?
+    unless target_defs
       node.raise "BUG: no target defs"
     end
 
@@ -2458,7 +2458,7 @@ class Crystal::Repl::Compiler < Crystal::Visitor
     end
 
     target_defs = call.target_defs
-    if target_defs.empty?
+    unless target_defs
       call.raise "BUG: no target defs"
     end
 

src/compiler/crystal/interpreter/multidispatch.cr

@@ -39,7 +39,7 @@ require "../semantic/main_visitor"
 # end
 # ```
 module Crystal::Repl::Multidispatch
-  def self.create_def(context : Context, node : Call, target_defs : ZeroOneOrMany(Def))
+  def self.create_def(context : Context, node : Call, target_defs : Array(Def))
     if node.block
       a_def = create_def_uncached(context, node, target_defs)
 
@@ -70,7 +70,7 @@ module Crystal::Repl::Multidispatch
     a_def
   end
 
-  private def self.create_def_uncached(context : Context, node : Call, target_defs : ZeroOneOrMany(Def))
+  private def self.create_def_uncached(context : Context, node : Call, target_defs : Array(Def))
     autocast_types = nil
 
     # The generated multidispatch method should handle autocasted
@@ -200,7 +200,7 @@ module Crystal::Repl::Multidispatch
         end
 
       call = Call.new(call_obj, node.name, call_args)
-      call.target_defs = ZeroOneOrMany(Def).new(target_def)
+      call.target_defs = [target_def]
       call.type = target_def.type
 
       if block

src/compiler/crystal/semantic/bindings.cr

@@ -1,7 +1,7 @@
 module Crystal
   class ASTNode
-    property dependencies = ZeroOneOrMany(ASTNode).new
-    property observers = ZeroOneOrMany(ASTNode).new
+    property! dependencies : Array(ASTNode)
+    property observers : Array(ASTNode)?
     property enclosing_call : Call?
 
     @dirty = false
@@ -107,17 +107,17 @@ module Crystal
     end
 
     def bind_to(node : ASTNode) : Nil
-      bind(node) do
-        @dependencies.push node
+      bind(node) do |dependencies|
+        dependencies.push node
         node.add_observer self
       end
     end
 
-    def bind_to(nodes : Indexable(ASTNode)) : Nil
+    def bind_to(nodes : Indexable) : Nil
       return if nodes.empty?
 
-      bind do
-        @dependencies.concat nodes
+      bind do |dependencies|
+        dependencies.concat nodes
         nodes.each &.add_observer self
       end
     end
@@ -130,7 +130,9 @@ module Crystal
         raise_frozen_type freeze_type, from_type, from
       end
 
-      yield
+      dependencies = @dependencies ||= [] of ASTNode
+
+      yield dependencies
 
       new_type = type_from_dependencies
       new_type = map_type(new_type) if new_type
@@ -151,28 +153,27 @@ module Crystal
       Type.merge dependencies
     end
 
-    def unbind_from(nodes : Nil) : Nil
+    def unbind_from(nodes : Nil)
       # Nothing to do
     end
 
-    def unbind_from(node : ASTNode) : Nil
-      @dependencies.reject! &.same?(node)
+    def unbind_from(node : ASTNode)
+      @dependencies.try &.reject! &.same?(node)
       node.remove_observer self
     end
 
-    def unbind_from(nodes : Enumerable(ASTNode)) : Nil
-      @dependencies.reject! { |dependency|
-        nodes.any? &.same?(dependency)
-      }
+    def unbind_from(nodes : Array(ASTNode))
+      @dependencies.try &.reject! { |dep| nodes.any? &.same?(dep) }
       nodes.each &.remove_observer self
     end
 
-    def add_observer(observer : ASTNode) : Nil
-      @observers.push observer
+    def add_observer(observer)
+      observers = @observers ||= [] of ASTNode
+      observers.push observer
     end
 
-    def remove_observer(observer : ASTNode) : Nil
-      @observers.reject! &.same?(observer)
+    def remove_observer(observer)
+      @observers.try &.reject! &.same?(observer)
     end
 
     def set_enclosing_call(enclosing_call)
@@ -194,9 +195,9 @@ module Crystal
     end
 
     def notify_observers
-      @observers.each &.update self
+      @observers.try &.each &.update self
       @enclosing_call.try &.recalculate
-      @observers.each &.propagate
+      @observers.try &.each &.propagate
       @enclosing_call.try &.propagate
     end
 
@@ -268,8 +269,8 @@ module Crystal
       visited = Set(ASTNode).new.compare_by_identity
       owner_trace << node if node.type?.try &.includes_type?(owner)
       visited.add node
-      until node.dependencies.empty?
-        dependencies = node.dependencies.select { |dep| dep.type? && dep.type.includes_type?(owner) && !visited.includes?(dep) }
+      while deps = node.dependencies?
+        dependencies = deps.select { |dep| dep.type? && dep.type.includes_type?(owner) && !visited.includes?(dep) }
         if dependencies.size > 0
           node = dependencies.first
           nil_reason = node.nil_reason if node.is_a?(MetaTypeVar)