[ruby/prism] Support offset

https://github.com/ruby/prism/commit/665f533373

lib/prism/ffi.rb

@@ -382,6 +382,9 @@ module Prism
       template << "l"
       values << options.fetch(:line, 1)
 
+      template << "L"
+      values << options.fetch(:offset, 0)
+
       template << "L"
       if (encoding = options[:encoding])
         name = encoding.name

prism/extension.c

@@ -23,13 +23,14 @@ VALUE rb_cPrismParseResult;
 
 VALUE rb_cPrismDebugEncoding;
 
-ID rb_option_id_filepath;
-ID rb_option_id_encoding;
-ID rb_option_id_line;
-ID rb_option_id_frozen_string_literal;
-ID rb_option_id_version;
-ID rb_option_id_scopes;
 ID rb_option_id_command_line;
+ID rb_option_id_encoding;
+ID rb_option_id_filepath;
+ID rb_option_id_frozen_string_literal;
+ID rb_option_id_line;
+ID rb_option_id_offset;
+ID rb_option_id_scopes;
+ID rb_option_id_version;
 
 /******************************************************************************/
 /* IO of Ruby code                                                            */
@@ -138,6 +139,8 @@ build_options_i(VALUE key, VALUE value, VALUE argument) {
         if (!NIL_P(value)) pm_options_encoding_set(options, rb_enc_name(rb_to_encoding(value)));
     } else if (key_id == rb_option_id_line) {
         if (!NIL_P(value)) pm_options_line_set(options, NUM2INT(value));
+    } else if (key_id == rb_option_id_offset) {
+        if (!NIL_P(value)) pm_options_offset_set(options, NUM2UINT(value));
     } else if (key_id == rb_option_id_frozen_string_literal) {
         if (!NIL_P(value)) pm_options_frozen_string_literal_set(options, value == Qtrue);
     } else if (key_id == rb_option_id_version) {
@@ -1297,13 +1300,14 @@ Init_prism(void) {
 
     // Intern all of the options that we support so that we don't have to do it
     // every time we parse.
-    rb_option_id_filepath = rb_intern_const("filepath");
-    rb_option_id_encoding = rb_intern_const("encoding");
-    rb_option_id_line = rb_intern_const("line");
-    rb_option_id_frozen_string_literal = rb_intern_const("frozen_string_literal");
-    rb_option_id_version = rb_intern_const("version");
-    rb_option_id_scopes = rb_intern_const("scopes");
     rb_option_id_command_line = rb_intern_const("command_line");
+    rb_option_id_encoding = rb_intern_const("encoding");
+    rb_option_id_filepath = rb_intern_const("filepath");
+    rb_option_id_frozen_string_literal = rb_intern_const("frozen_string_literal");
+    rb_option_id_line = rb_intern_const("line");
+    rb_option_id_offset = rb_intern_const("offset");
+    rb_option_id_scopes = rb_intern_const("scopes");
+    rb_option_id_version = rb_intern_const("version");
 
     /**
      * The version of the prism library.

prism/options.c

@@ -24,6 +24,14 @@ pm_options_line_set(pm_options_t *options, int32_t line) {
     options->line = line;
 }
 
+/**
+ * Set the offset option on the given options struct.
+ */
+PRISM_EXPORTED_FUNCTION void
+pm_options_offset_set(pm_options_t *options, uint32_t offset) {
+    options->offset = offset;
+}
+
 /**
  * Set the frozen string literal option on the given options struct.
  */
@@ -193,6 +201,9 @@ pm_options_read(pm_options_t *options, const char *data) {
     options->line = pm_options_read_s32(data);
     data += 4;
 
+    options->offset = pm_options_read_u32(data);
+    data += 4;
+
     uint32_t encoding_length = pm_options_read_u32(data);
     data += 4;
 

prism/options.h

@@ -50,6 +50,12 @@ typedef struct {
      */
     int32_t line;
 
+    /**
+     * The offset within the file that the parse starts on. This value is
+     * 0-indexed.
+     */
+    uint32_t offset;
+
     /**
      * The name of the encoding that the source file is in. Note that this must
      * correspond to a name that can be found with Encoding.find in Ruby.
@@ -136,6 +142,14 @@ PRISM_EXPORTED_FUNCTION void pm_options_filepath_set(pm_options_t *options, cons
  */
 PRISM_EXPORTED_FUNCTION void pm_options_line_set(pm_options_t *options, int32_t line);
 
+/**
+ * Set the offset option on the given options struct.
+ *
+ * @param options The options struct to set the offset on.
+ * @param offset The offset to set.
+ */
+PRISM_EXPORTED_FUNCTION void pm_options_offset_set(pm_options_t *options, uint32_t offset);
+
 /**
  * Set the encoding option on the given options struct.
  *
@@ -231,6 +245,7 @@ PRISM_EXPORTED_FUNCTION void pm_options_free(pm_options_t *options);
  * | `4`     | the length of the filepath |
  * | ...     | the filepath bytes         |
  * | `4`     | the line number            |
+ * | `4`     | the offset                 |
  * | `4`     | the length the encoding    |
  * | ...     | the encoding bytes         |
  * | `1`     | frozen string literal      |

prism/prism.c

@@ -18781,6 +18781,22 @@ pm_parser_init(pm_parser_t *parser, const uint8_t *source, size_t size, const pm
         // line option
         parser->start_line = options->line;
 
+        // offset option
+        if (options->offset != 0) {
+            const uint8_t *cursor = parser->start;
+            const uint8_t *offset = cursor + options->offset;
+
+            const uint8_t *newline = NULL;
+            while ((newline = next_newline(cursor, parser->end - cursor)) != NULL) {
+                if (newline > offset) break;
+                pm_newline_list_append(&parser->newline_list, newline);
+                cursor = newline + 1;
+            }
+
+            parser->previous = (pm_token_t) { .type = PM_TOKEN_EOF, .start = offset, .end = offset };
+            parser->current = (pm_token_t) { .type = PM_TOKEN_EOF, .start = offset, .end = offset };
+        }
+
         // encoding option
         size_t encoding_length = pm_string_length(&options->encoding);
         if (encoding_length > 0) {

test/prism/ruby_api_test.rb

@@ -231,6 +231,21 @@ module Prism
       assert_equal 16, base[parse_expression("0x1")]
     end
 
+    def test_offset
+      source = <<~RUBY
+        #!/bin/sh
+
+        echo "foo"
+        exit 0
+
+        #!/usr/bin/env ruby
+
+        puts "bar"
+      RUBY
+
+      assert Prism.parse_success?(source, offset: 30)
+    end
+
     private
 
     def parse_expression(source)