Implement translation for it keyword

Author: amomchilov

parser/prism/Translator.cc

@@ -862,8 +862,14 @@ std::unique_ptr<parser::Node> Translator::translate(pm_node_t *node) {
         case PM_INTERPOLATED_REGULAR_EXPRESSION_NODE:
         case PM_INTERPOLATED_SYMBOL_NODE:
         case PM_INTERPOLATED_X_STRING_NODE:
-        case PM_IT_LOCAL_VARIABLE_READ_NODE:
-        case PM_IT_PARAMETERS_NODE:
+        case PM_IT_LOCAL_VARIABLE_READ_NODE: {
+            // See Prism::ParserStorage::ParsedRubyVersion
+            unreachable("The `it` keyword was introduced in Ruby 3.4, which isn't supported by Sorbet yet.");
+        }
+        case PM_IT_PARAMETERS_NODE: {
+            // See Prism::ParserStorage::ParsedRubyVersion
+            unreachable("The `it` keyword was introduced in Ruby 3.4, which isn't supported by Sorbet yet.");
+        }
         case PM_LAMBDA_NODE:
         case PM_MATCH_LAST_LINE_NODE:
         case PM_MATCH_PREDICATE_NODE:

test/prism_regression/keyword_it.parse-tree.exp

@@ -0,0 +1,49 @@
+Begin {
+  stmts = [
+    Block {
+      send = Send {
+        receiver = Const {
+          scope = NULL
+          name = <C <U Proc>>
+        }
+        method = <U new>
+        args = [
+        ]
+      }
+      args = NULL
+      body = Send {
+        receiver = NULL
+        method = <U it>
+        args = [
+        ]
+      }
+    }
+    Block {
+      send = Send {
+        receiver = Const {
+          scope = NULL
+          name = <C <U Proc>>
+        }
+        method = <U new>
+        args = [
+        ]
+      }
+      args = NULL
+      body = Begin {
+        stmts = [
+          Assign {
+            lhs = LVarLhs {
+              name = <U it>
+            }
+            rhs = Integer {
+              val = "123"
+            }
+          }
+          LVar {
+            name = <U it>
+          }
+        ]
+      }
+    }
+  ]
+}

test/prism_regression/keyword_it.rb

@@ -0,0 +1,15 @@
+# typed: false
+
+# The `it` keyword was introduced in Ruby 3.4, which isn't supported by Sorbet yet.
+# https://bugs.ruby-lang.org/issues/18980
+#
+# For now, we'll just treat it like a local variable read or method call.
+
+Proc.new do
+  it # Prior to Ruby 3.4, this would just be a regular method call
+end
+
+Proc.new do
+  it = 123 # Prior to Ruby 3.4, this would just be a local variable write
+  it       # ... and this is a local variable read.
+end