Add `node_id_for_backtrace_location` function

We want to use error highlight with eval'd code, specifically ERB
templates. We're able to recover the generated code for eval'd templates
and can get a parse tree for the ERB generated code, but we don't have a
way to get the node id from the backtrace location. So we can't pass the
right node into error highlight.

This patch gives us an API to get the node id from the backtrace
location so we can find the node in the AST.

Error Highlight PR: https://github.com/ruby/error_highlight/pull/26

Co-authored-by: Aaron Patterson <tenderlove@ruby-lang.org>

ast.c

@@ -195,6 +195,18 @@ script_lines(VALUE path)
     return lines;
 }
 
+static VALUE
+node_id_for_backtrace_location(rb_execution_context_t *ec, VALUE module, VALUE location)
+{
+    int node_id;
+    node_id = rb_get_node_id_from_frame_info(location);
+    if (node_id == -1) {
+        return Qnil;
+    }
+
+    return INT2NUM(node_id);
+}
+
 static VALUE
 ast_s_of(rb_execution_context_t *ec, VALUE module, VALUE body, VALUE keep_script_lines, VALUE error_tolerant)
 {

ast.rb

@@ -67,6 +67,21 @@ module RubyVM::AbstractSyntaxTree
     Primitive.ast_s_of body, keep_script_lines, error_tolerant
   end
 
+  #  call-seq:
+  #     RubyVM::AbstractSyntaxTree.node_id_for_backtrace_location(backtrace_location)   -> integer
+  #
+  #   Returns the node id for the given backtrace location.
+  #
+  #     begin
+  #       raise
+  #     rescue =>  e
+  #       loc = e.backtrace_locations.first
+  #       RubyVM::AbstractSyntaxTree.node_id_for_backtrace_location(loc)
+  #     end # => 0
+  def self.node_id_for_backtrace_location backtrace_location
+    Primitive.node_id_for_backtrace_location backtrace_location
+  end
+
   # RubyVM::AbstractSyntaxTree::Node instances are created by parse methods in
   # RubyVM::AbstractSyntaxTree.
   #

test/ruby/test_ast.rb

@@ -186,6 +186,19 @@ class TestAst < Test::Unit::TestCase
     end
   end
 
+  def test_node_id_for_location
+    exception = begin
+                  raise
+                rescue => e
+                  e
+                end
+    loc = exception.backtrace_locations.first
+    node_id = RubyVM::AbstractSyntaxTree.node_id_for_backtrace_location(loc)
+    node = RubyVM::AbstractSyntaxTree.of(loc, keep_script_lines: true)
+
+    assert_equal node.node_id, node_id
+  end
+
   def test_of_proc_and_method
     proc = Proc.new { 1 + 2 }
     method = self.method(__method__)