Fixed #2059: regression with class variables not being correctly typed

spec/compiler/type_inference/class_var_spec.cr

@@ -169,4 +169,17 @@ describe "Type inference: class var" do
       ),
       "can't use class variable with generic types, only with generic types instances"
   end
+
+  it "types class var as nil if assigned for the first time inside method (#2059)" do
+    assert_type("
+      class Foo
+        def self.foo
+          @@foo = 1
+          @@foo
+        end
+      end
+
+      Foo.foo
+      ") { nilable int32 }
+  end
 end

spec/compiler/type_inference/type_declaration_spec.cr

@@ -122,7 +122,7 @@ describe "Type inference: type declaration" do
 
       Foo.x = true
       ),
-      "type must be Int32, not Bool"
+      "type must be Int32, not Nil"
   end
 
   it "declares class variable (2)" do

src/compiler/crystal/semantic/type_visitor.cr

@@ -541,9 +541,11 @@ module Crystal
       var = mod.global_vars[target.name]?
       unless var
         var = Var.new(target.name)
-        if @typed_def
-          var.bind_to mod.nil_var
-        end
+
+        # If we are assigning to a global inside a method, make it nilable
+        # if this is the first time we are assigning to it, because
+        # the method might be called conditionally
+        var.bind_to mod.nil_var if @typed_def
         mod.global_vars[target.name] = var
       end
       var.add_attributes(target.attributes)
@@ -555,7 +557,10 @@ module Crystal
     end
 
     def type_assign(target : ClassVar, value, node)
-      var = lookup_class_var target, bind_to_nil_if_non_existent: false
+      # If we are assigning to a class variable inside a method, make it nilable
+      # if this is the first time we are assigning to it, because
+      # the method might be called conditionally
+      var = lookup_class_var target, bind_to_nil_if_non_existent: !!@typed_def
       check_valid_attributes var, ValidClassVarAttributes, "class variable"
 
       value.accept self