`RubyVM.keep_script_lines`

`RubyVM.keep_script_lines` enables to keep script lines
for each ISeq and AST. This feature is for debugger/REPL
support.

```ruby
RubyVM.keep_script_lines = true
RubyVM::keep_script_lines = true

eval("def foo = nil\ndef bar = nil")
pp RubyVM::InstructionSequence.of(method(:foo)).script_lines
```

1 files changed, 40 insertions, 4 deletions

diff --git a/iseq.c b/iseq.c
index 68611798c7..0551e0c99a 100644
--- a/iseq.c
+++ b/iseq.c
@@ -595,7 +595,8 @@ new_arena(void)
 static VALUE
 prepare_iseq_build(rb_iseq_t *iseq,
                    VALUE name, VALUE path, VALUE realpath, VALUE first_lineno, const rb_code_location_t *code_location, const int node_id,
-		   const rb_iseq_t *parent, int isolated_depth, enum iseq_type type, const rb_compile_option_t *option)
+		   const rb_iseq_t *parent, int isolated_depth, enum iseq_type type,
+                   VALUE script_lines, const rb_compile_option_t *option)
 {
     VALUE coverage = Qfalse;
     VALUE err_info = Qnil;
@@ -616,6 +617,8 @@ prepare_iseq_build(rb_iseq_t *iseq,
     ISEQ_ORIGINAL_ISEQ_CLEAR(iseq);
     body->variable.flip_count = 0;
 
+    RB_OBJ_WRITE(iseq, &body->variable.script_lines, script_lines);
+
     ISEQ_COMPILE_DATA_ALLOC(iseq);
     RB_OBJ_WRITE(iseq, &ISEQ_COMPILE_DATA(iseq)->err_info, err_info);
     RB_OBJ_WRITE(iseq, &ISEQ_COMPILE_DATA(iseq)->catch_table_ary, Qnil);
@@ -894,7 +897,17 @@ rb_iseq_new_with_opt(const rb_ast_body_t *ast, VALUE name, VALUE path, VALUE rea
     }
     if (ast && ast->compile_option) rb_iseq_make_compile_option(&new_opt, ast->compile_option);
 
-    prepare_iseq_build(iseq, name, path, realpath, first_lineno, node ? &node->nd_loc : NULL, node ? nd_node_id(node) : -1, parent, isolated_depth, type, &new_opt);
+    VALUE script_lines = Qnil;
+
+    if (ast && !FIXNUM_P(ast->script_lines) && ast->script_lines) {
+        script_lines = ast->script_lines;
+    }
+    else if (parent) {
+        script_lines = parent->body->variable.script_lines;
+    }
+
+    prepare_iseq_build(iseq, name, path, realpath, first_lineno, node ? &node->nd_loc : NULL, node ? nd_node_id(node) : -1,
+                       parent, isolated_depth, type, script_lines, &new_opt);
 
     rb_iseq_compile_node(iseq, node);
     finish_iseq_build(iseq);
@@ -913,7 +926,7 @@ rb_iseq_new_with_callback(
     rb_iseq_t *iseq = iseq_alloc();
 
     if (!option) option = &COMPILE_OPTION_DEFAULT;
-    prepare_iseq_build(iseq, name, path, realpath, first_lineno, NULL, -1, parent, 0, type, option);
+    prepare_iseq_build(iseq, name, path, realpath, first_lineno, NULL, -1, parent, 0, type, Qnil, option);
 
     rb_iseq_compile_callback(iseq, ifunc);
     finish_iseq_build(iseq);
@@ -1026,7 +1039,7 @@ iseq_load(VALUE data, const rb_iseq_t *parent, VALUE opt)
     make_compile_option(&option, opt);
     option.peephole_optimization = FALSE; /* because peephole optimization can modify original iseq */
     prepare_iseq_build(iseq, name, path, realpath, first_lineno, &tmp_loc, NUM2INT(node_id),
-                       parent, 0, (enum iseq_type)iseq_type, &option);
+                       parent, 0, (enum iseq_type)iseq_type, Qnil, &option);
 
     rb_iseq_build_from_ary(iseq, misc, locals, params, exception, body);
 
@@ -3680,6 +3693,26 @@ succ_index_lookup(const struct succ_index_table *sd, int x)
 }
 #endif
 
+
+/*
+ *  call-seq:
+ *     iseq.script_lines -> array or nil
+ *
+ *  It returns recorded script lines if it is availalble.
+ *  The script lines are not limited to the iseq range, but
+ *  are entire lines of the source file.
+ *
+ *  Note that this is an API for ruby internal use, debugging,
+ *  and research. Do not use this for any other purpose.
+ *  The compatibility is not guaranteed.
+ */
+static VALUE
+iseqw_script_lines(VALUE self)
+{
+    const rb_iseq_t *iseq = iseqw_check(self);
+    return iseq->body->variable.script_lines;
+}
+
 /*
  *  Document-class: RubyVM::InstructionSequence
  *
@@ -3747,6 +3780,9 @@ Init_ISeq(void)
     rb_define_singleton_method(rb_cISeq, "disassemble", iseqw_s_disasm, 1);
     rb_define_singleton_method(rb_cISeq, "of", iseqw_s_of, 1);
 
+    // script lines
+    rb_define_method(rb_cISeq, "script_lines", iseqw_script_lines, 0);
+
     rb_undef_method(CLASS_OF(rb_cISeq), "translate");
     rb_undef_method(CLASS_OF(rb_cISeq), "load_iseq");
 }