Compiler: declare all instance vars initializers before typing them. F…

…ixes #3988

spec/compiler/semantic/instance_var_spec.cr

@@ -4640,4 +4640,49 @@ describe "Semantic: instance var" do
       ),
       "Can't infer the type of instance variable '@baz' of Foo"
   end
+
+  it "instance variables initializers are used in class variables initialized objects (#3988)" do
+    assert_type(%(
+       class Foo
+         @@foo = Foo.new
+
+        @never_nil = 1
+
+        def initialize
+          if false
+            @never_nil = 2
+          end
+        end
+      end
+
+      Foo.new.@never_nil
+      )) { int32 }
+  end
+
+  it "allow usage of instance variable initializer from instance variable initializer" do
+    assert_type(%(
+      class Foo
+        @bar = Bar.new
+        @never_nil = 1
+
+        def initialize
+          if false
+            @never_nil = 2
+          end
+        end
+      end
+
+      class Bar
+        @never_nil = 1
+
+        def initialize
+          if false
+            @never_nil = 2
+          end
+        end
+      end
+
+      {Foo.new.@never_nil, Bar.new.@never_nil}
+    )) { tuple_of([int32, int32]) }
+  end
 end

src/compiler/crystal/semantic.cr

@@ -21,6 +21,12 @@ class Crystal::Program
   def semantic(node : ASTNode, cleanup = true) : ASTNode
     node, processor = top_level_semantic(node)
 
+    Crystal.timing("Semantic (ivars initializers)", @wants_stats) do
+      visitor = InstanceVarsInitializerVisitor.new(self)
+      visit_with_finished_hooks(node, visitor)
+      visitor.finish
+    end
+
     Crystal.timing("Semantic (cvars initializers)", @wants_stats) do
       visit_class_vars_initializers(node)
     end
@@ -29,11 +35,6 @@ class Crystal::Program
     # give an error otherwise
     processor.check_non_nilable_class_vars_without_initializers
 
-    Crystal.timing("Semantic (ivars initializers)", @wants_stats) do
-      visitor = InstanceVarsInitializerVisitor.new(self)
-      visit_with_finished_hooks(node, visitor)
-    end
-
     result = Crystal.timing("Semantic (main)", @wants_stats) do
       visit_main(node, process_finished_hooks: true, cleanup: cleanup)
     end

src/compiler/crystal/semantic/instance_vars_initializer_visitor.cr

@@ -26,6 +26,9 @@ require "./semantic_visitor"
 # end
 # ```
 class Crystal::InstanceVarsInitializerVisitor < Crystal::SemanticVisitor
+  record Initializer, scope : Type, target : InstanceVar, value : ASTNode, meta_vars : MetaVars
+  getter initializers = [] of Initializer
+
   def visit_any(node)
     case node
     when Assign
@@ -60,21 +63,33 @@ class Crystal::InstanceVarsInitializerVisitor < Crystal::SemanticVisitor
     when Program, FileModule
       node.raise "can't use instance variables at the top level"
     when ClassType, NonGenericModuleType, GenericModuleType
-      meta_vars = MetaVars.new
-      ivar_visitor = MainVisitor.new(program, meta_vars: meta_vars)
-      ivar_visitor.scope = current_type
+      initializers << Initializer.new(current_type, target, value, MetaVars.new)
+      node.type = @program.nil
+      return
+    end
+  end
 
-      unless current_type.is_a?(GenericType)
-        value.accept ivar_visitor
+  def finish
+    # First declare them, so when we type all of them we will have
+    # the info of which instance vars have initializers (so they are not nil)
+    initializers.each do |i|
+      scope = i.scope
+      unless scope.lookup_instance_var?(i.target.name)
+        program.undefined_instance_variable(i.target, scope, nil)
       end
 
-      unless current_type.lookup_instance_var?(target.name)
-        ivar_visitor.undefined_instance_variable(current_type, target)
-      end
+      scope.add_instance_var_initializer(i.target.name, i.value, scope.is_a?(GenericType) ? nil : i.meta_vars)
+    end
 
-      current_type.add_instance_var_initializer(target.name, value, current_type.is_a?(GenericType) ? nil : meta_vars)
-      node.type = @program.nil
-      return
+    # Now type them
+    initializers.each do |i|
+      scope = i.scope
+
+      unless scope.is_a?(GenericType)
+        ivar_visitor = MainVisitor.new(program, meta_vars: i.meta_vars)
+        ivar_visitor.scope = scope
+        i.value.accept ivar_visitor
+      end
     end
   end
 end