[ruby/prism] Raise diagnostics for parser

https://github.com/ruby/prism/commit/102b4a16f5

lib/prism/translation/parser.rb

@@ -9,6 +9,20 @@ module Prism
     # the parser gem, and overrides the parse* methods to parse with prism and
     # then translate.
     class Parser < ::Parser::Base
+      # The parser gem has a list of diagnostics with a hard-coded set of error
+      # messages. We create our own diagnostic class in order to set our own
+      # error messages.
+      class Diagnostic < ::Parser::Diagnostic
+        # The message generated by prism.
+        attr_reader :message
+
+        # Initialize a new diagnostic with the given message and location.
+        def initialize(message, location)
+          @message = message
+          super(:error, :prism_error, {}, location, [])
+        end
+      end
+
       Racc_debug_parser = false # :nodoc:
 
       def version # :nodoc:
@@ -28,10 +42,9 @@ module Prism
         @source_buffer = source_buffer
         source = source_buffer.source
 
-        build_ast(
-          Prism.parse(source, filepath: source_buffer.name).value,
-          build_offset_cache(source)
-        )
+        result = unwrap(Prism.parse(source, filepath: source_buffer.name))
+
+        build_ast(result.value, build_offset_cache(source))
       ensure
         @source_buffer = nil
       end
@@ -42,7 +55,7 @@ module Prism
         source = source_buffer.source
 
         offset_cache = build_offset_cache(source)
-        result = Prism.parse(source, filepath: source_buffer.name)
+        result = unwrap(Prism.parse(source, filepath: source_buffer.name))
 
         [
           build_ast(result.value, offset_cache),
@@ -59,7 +72,8 @@ module Prism
         source = source_buffer.source
 
         offset_cache = build_offset_cache(source)
-        result = Prism.parse_lex(source, filepath: source_buffer.name)
+        result = unwrap(Prism.parse_lex(source, filepath: source_buffer.name))
+
         program, tokens = result.value
 
         [
@@ -79,6 +93,18 @@ module Prism
 
       private
 
+      # If there was a error generated during the parse, then raise an
+      # appropriate syntax error. Otherwise return the result.
+      def unwrap(result)
+        return result if result.success?
+
+        error = result.errors.first
+        offset_cache = build_offset_cache(source_buffer.source)
+
+        diagnostic = Diagnostic.new(error.message, build_range(error.location, offset_cache))
+        raise ::Parser::SyntaxError, diagnostic
+      end
+
       # Prism deals with offsets in bytes, while the parser gem deals with
       # offsets in characters. We need to handle this conversion in order to
       # build the parser gem AST.
@@ -109,15 +135,7 @@ module Prism
       # Build the parser gem comments from the prism comments.
       def build_comments(comments, offset_cache)
         comments.map do |comment|
-          location = comment.location
-
-          ::Parser::Source::Comment.new(
-            ::Parser::Source::Range.new(
-              source_buffer,
-              offset_cache[location.start_offset],
-              offset_cache[location.end_offset]
-            )
-          )
+          ::Parser::Source::Comment.new(build_range(comment.location, offset_cache))
         end
       end
 
@@ -126,6 +144,15 @@ module Prism
         Lexer.new(source_buffer, tokens.map(&:first), offset_cache).to_a
       end
 
+      # Build a range from a prism location.
+      def build_range(location, offset_cache)
+        ::Parser::Source::Range.new(
+          source_buffer,
+          offset_cache[location.start_offset],
+          offset_cache[location.end_offset]
+        )
+      end
+
       require_relative "parser/compiler"
       require_relative "parser/lexer"
 

lib/prism/translation/parser/compiler.rb

@@ -83,11 +83,16 @@ module Prism
           elements = [*node.requireds]
           elements << node.rest if !node.rest.nil? && !node.rest.is_a?(ImplicitRestNode)
           elements.concat(node.posts)
+          visited = visit_all(elements)
+
+          if node.rest.is_a?(ImplicitRestNode)
+            visited[-1] = builder.match_with_trailing_comma(visited[-1], token(node.rest.location))
+          end
 
           if node.constant
-            builder.const_pattern(visit(node.constant), token(node.opening_loc), builder.array_pattern(nil, visit_all(elements), nil), token(node.closing_loc))
+            builder.const_pattern(visit(node.constant), token(node.opening_loc), builder.array_pattern(nil, visited, nil), token(node.closing_loc))
           else
-            builder.array_pattern(token(node.opening_loc), visit_all(elements), token(node.closing_loc))
+            builder.array_pattern(token(node.opening_loc), visited, token(node.closing_loc))
           end
         end