Add specs for the it variable in blocks

Author: herwinw

language/block_spec.rb

@@ -1049,6 +1049,12 @@ def all_kwrest(arg1, arg2, *rest, post1, post2, kw1: 1, kw2: 2, okw1:, okw2:, **
       }.should complain(/warning: `it` calls without arguments will refer to the first block param in Ruby 3.4; use it\(\) or self.it/)
     end
 
+    it "emits a deprecation warning if numbered parameters are used" do
+      -> {
+        eval "proc { it; _1 }"
+      }.should complain(/warning: `it` calls without arguments will refer to the first block param in Ruby 3.4; use it\(\) or self.it/)
+    end
+
     it "does not emit a deprecation warning when a block has parameters" do
       -> { eval "proc { |a, b| it }" }.should_not complain
       -> { eval "proc { |*rest| it }" }.should_not complain
@@ -1058,21 +1064,71 @@ def all_kwrest(arg1, arg2, *rest, post1, post2, kw1: 1, kw2: 2, okw1:, okw2:, **
       -> { eval "proc { |**| it }" }.should_not complain
       -> { eval "proc { |&block| it }" }.should_not complain
       -> { eval "proc { |&| it }" }.should_not complain
+      -> { eval "proc { || it }" }.should_not complain
     end
 
     it "does not emit a deprecation warning when `it` calls with arguments" do
       -> { eval "proc { it(42) }" }.should_not complain
+      -> { eval "proc { it 42 }" }.should_not complain
+    end
+
+    it "does not emit a deprecation warning when `it` calls with a block" do
+      -> { eval "proc { it {} }" }.should_not complain
+    end
+
+    it "does not emit a deprecation warning when a local variable inside the block named `it` exists" do
+      -> { eval "proc { it = 42; it }" }.should_not complain
     end
 
     it "does not emit a deprecation warning when `it` calls with explicit empty arguments list" do
       -> { eval "proc { it() }" }.should_not complain
     end
+
+    it "calls the method `it` if defined" do
+      o = Object.new
+      def o.it
+        21
+      end
+      suppress_warning do
+        o.instance_eval("proc { it * 2 }").call(1).should == 42
+      end
+    end
+  end
+
+  ruby_version_is "3.4" do
+    it "does not emit a deprecation warning" do
+      -> {
+        eval "proc { it }"
+      }.should_not complain
+    end
+
+    it "acts as the first argument if no local variables exist" do
+      eval("proc { it * 2 }").call(5).should == 10
+    end
+
+    it "can be reassigned to act as a local variable" do
+      eval("proc { tmp = it; it = tmp * 2; it }").call(21).should == 42
+    end
+
+    it "can be used in nested calls" do
+      eval("proc { it.map { it * 2 } }").call([1, 2, 3]).should == [2, 4, 6]
+    end
+
+    it "cannot be mixed with numbered parameters" do
+      -> {
+        eval "proc { it + _1 }"
+      }.should raise_error(SyntaxError, /numbered parameters are not allowed when 'it' is already used/)
+    end
   end
 end
 
-describe "if `it` is defined outside of a block" do
-  it "treats `it` as a captured variable" do
+describe "if `it` is defined as a variable" do
+  it "treats `it` as a captured variable if defined outside of a block" do
     it = 5
     proc { it }.call(0).should == 5
   end
+
+  it "treats `it` as a local variable if defined inside of a block" do
+    proc { it = 5; it }.call(0).should == 5
+  end
 end