Fix support for 'it' implicit local variable

Author: kddnewton

config.yml

@@ -2570,6 +2570,12 @@ nodes:
 
           `foo #{bar} baz`
           ^^^^^^^^^^^^^^^^
+  - name: ItLocalVariableReadNode
+    comment: |
+      Represents reading from the implicit `it` local variable.
+
+          -> { it }
+               ^^
   - name: ItParametersNode
     comment: |
       Represents an implicit set of parameters through the use of the `it` keyword within a block or lambda.
@@ -2695,10 +2701,6 @@ nodes:
 
               _1     # name `:_1`
 
-          Finally, for the default `it` block parameter, the name is `0it`. This is to distinguish it from an `it` local variable that is explicitly declared.
-
-              it     # name `:0it`
-
       - name: depth
         type: uint32
         comment: |

include/prism/parser.h

@@ -546,6 +546,17 @@ typedef struct pm_locals {
     pm_local_t *locals;
 } pm_locals_t;
 
+/** The flags about scope parameters that can be set. */
+typedef uint8_t pm_scope_parameters_t;
+static const pm_scope_parameters_t PM_SCOPE_PARAMETERS_NONE = 0x0;
+static const pm_scope_parameters_t PM_SCOPE_PARAMETERS_FORWARDING_POSITIONALS = 0x1;
+static const pm_scope_parameters_t PM_SCOPE_PARAMETERS_FORWARDING_KEYWORDS = 0x2;
+static const pm_scope_parameters_t PM_SCOPE_PARAMETERS_FORWARDING_BLOCK = 0x4;
+static const pm_scope_parameters_t PM_SCOPE_PARAMETERS_FORWARDING_ALL = 0x8;
+static const pm_scope_parameters_t PM_SCOPE_PARAMETERS_IMPLICIT_DISALLOWED = 0x10;
+static const pm_scope_parameters_t PM_SCOPE_PARAMETERS_NUMBERED_INNER = 0x20;
+static const pm_scope_parameters_t PM_SCOPE_PARAMETERS_NUMBERED_FOUND = 0x40;
+
 /**
  * This struct represents a node in a linked list of scopes. Some scopes can see
  * into their parent scopes, while others cannot.
@@ -557,10 +568,19 @@ typedef struct pm_scope {
     /** The IDs of the locals in the given scope. */
     pm_locals_t locals;
 
+    /**
+     * This is a list of the implicit parameters contained within the block.
+     * These will be processed after the block is parsed to determine the kind
+     * of parameters node that should be used and to check if any errors need to
+     * be added.
+     */
+    pm_node_list_t implicit_parameters;
+
     /**
      * This is a bitfield that indicates the parameters that are being used in
-     * this scope. It is a combination of the PM_SCOPE_PARAMS_* constants. There
-     * are three different kinds of parameters that can be used in a scope:
+     * this scope. It is a combination of the PM_SCOPE_PARAMETERS_* constants.
+     * There are three different kinds of parameters that can be used in a
+     * scope:
      *
      * - Ordinary parameters (e.g., def foo(bar); end)
      * - Numbered parameters (e.g., def foo; _1; end)
@@ -575,15 +595,7 @@ typedef struct pm_scope {
      * - def foo(&); end
      * - def foo(...); end
      */
-    uint8_t parameters;
-
-    /**
-     * An integer indicating the number of numbered parameters on this scope.
-     * This is necessary to determine if child blocks are allowed to use
-     * numbered parameters, and to pass information to consumers of the AST
-     * about how many numbered parameters exist.
-     */
-    int8_t numbered_parameters;
+    pm_scope_parameters_t parameters;
 
     /**
      * The current state of constant shareability for this scope. This is
@@ -598,21 +610,6 @@ typedef struct pm_scope {
     bool closed;
 } pm_scope_t;
 
-static const uint8_t PM_SCOPE_PARAMETERS_NONE = 0x0;
-static const uint8_t PM_SCOPE_PARAMETERS_ORDINARY = 0x1;
-static const uint8_t PM_SCOPE_PARAMETERS_NUMBERED = 0x2;
-static const uint8_t PM_SCOPE_PARAMETERS_IT = 0x4;
-static const uint8_t PM_SCOPE_PARAMETERS_TYPE_MASK = 0x7;
-
-static const uint8_t PM_SCOPE_PARAMETERS_FORWARDING_POSITIONALS = 0x8;
-static const uint8_t PM_SCOPE_PARAMETERS_FORWARDING_KEYWORDS = 0x10;
-static const uint8_t PM_SCOPE_PARAMETERS_FORWARDING_BLOCK = 0x20;
-static const uint8_t PM_SCOPE_PARAMETERS_FORWARDING_ALL = 0x40;
-
-static const int8_t PM_SCOPE_NUMBERED_PARAMETERS_INNER = -2;
-static const int8_t PM_SCOPE_NUMBERED_PARAMETERS_DISALLOWED = -1;
-static const int8_t PM_SCOPE_NUMBERED_PARAMETERS_NONE = 0;
-
 /**
  * A struct that represents a stack of boolean values.
  */

lib/prism/translation/parser/compiler.rb

@@ -1148,6 +1148,12 @@ def visit_interpolated_x_string_node(node)
           end
         end
 
+        # -> { it }
+        #      ^^
+        def visit_it_local_variable_read_node(node)
+          builder.ident([:it, srange(node.location)]).updated(:lvar)
+        end
+
         # -> { it }
         # ^^^^^^^^^
         def visit_it_parameters_node(node)
@@ -1201,14 +1207,7 @@ def visit_lambda_node(node)
         # foo
         # ^^^
         def visit_local_variable_read_node(node)
-          name = node.name
-
-          # This is just a guess. parser doesn't have support for the implicit
-          # `it` variable yet, so we'll probably have to visit this once it
-          # does.
-          name = :it if name == :"0it"
-
-          builder.ident([name, srange(node.location)]).updated(:lvar)
+          builder.ident([node.name, srange(node.location)]).updated(:lvar)
         end
 
         # foo = 1

lib/prism/translation/ripper.rb

@@ -2217,6 +2217,13 @@ def visit_interpolated_x_string_node(node)
         end
       end
 
+      # -> { it }
+      #      ^^
+      def visit_it_local_variable_read_node(node)
+        bounds(node.location)
+        on_vcall(on_ident(node.slice))
+      end
+
       # -> { it }
       # ^^^^^^^^^
       def visit_it_parameters_node(node)
@@ -2312,12 +2319,7 @@ def visit_lambda_node(node)
       # ^^^
       def visit_local_variable_read_node(node)
         bounds(node.location)
-
-        if node.name == :"0it"
-          on_vcall(on_ident(node.slice))
-        else
-          on_var_ref(on_ident(node.slice))
-        end
+        on_var_ref(on_ident(node.slice))
       end
 
       # foo = 1

lib/prism/translation/ruby_parser.rb

@@ -916,6 +916,12 @@ def visit_interpolated_x_string_node(node)
           end
         end
 
+        # -> { it }
+        #      ^^
+        def visit_it_local_variable_read_node(node)
+          s(node, :call, nil, :it)
+        end
+
         # foo(bar: baz)
         #     ^^^^^^^^
         def visit_keyword_hash_node(node)