[ruby/prism] Add some samples for using prism APIs

https://github.com/ruby/prism/commit/6a4fe21088

sample/find_comments.rb

@@ -0,0 +1,22 @@
+# This script finds all of the comments within a given source file.
+
+require "prism"
+
+Prism.parse_comments(DATA.read).each do |comment|
+  puts comment.inspect
+  puts comment.slice
+end
+
+# =>
+# #<Prism::InlineComment @location=#<Prism::Location @start_offset=0 @length=42 start_line=1>>
+# # This is documentation for the Foo class.
+# #<Prism::InlineComment @location=#<Prism::Location @start_offset=55 @length=43 start_line=3>>
+# # This is documentation for the bar method.
+
+__END__
+# This is documentation for the Foo class.
+class Foo
+  # This is documentation for the bar method.
+  def bar
+  end
+end

sample/find_nodes.rb

@@ -0,0 +1,41 @@
+# This script finds all of the nodes of a specific type within a given source
+# file. It uses the visitor class to traverse the AST.
+
+require "prism"
+
+class RegexpVisitor < Prism::Visitor
+  def initialize(regexps)
+    @regexps = regexps
+  end
+
+  def visit_regular_expression_node(node)
+    @regexps << node
+    super
+  end
+end
+
+result = Prism.parse_stream(DATA)
+regexps = []
+
+result.value.accept(RegexpVisitor.new(regexps))
+puts regexps.map(&:inspect)
+
+# =>
+# @ RegularExpressionNode (location: (2,9)-(2,14))
+# ├── flags: forced_us_ascii_encoding
+# ├── opening_loc: (2,9)-(2,10) = "/"
+# ├── content_loc: (2,10)-(2,13) = "foo"
+# ├── closing_loc: (2,13)-(2,14) = "/"
+# └── unescaped: "foo"
+# @ RegularExpressionNode (location: (3,9)-(3,14))
+# ├── flags: forced_us_ascii_encoding
+# ├── opening_loc: (3,9)-(3,10) = "/"
+# ├── content_loc: (3,10)-(3,13) = "bar"
+# ├── closing_loc: (3,13)-(3,14) = "/"
+# └── unescaped: "bar"
+
+__END__
+class Foo
+  REG1 = /foo/
+  REG2 = /bar/
+end

sample/locate_nodes.rb

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+# This script locates a set of nodes determined by a line and column (in bytes).
+
+require "prism"
+
+def locate(node, line:, column:)
+  queue = [node]
+  result = []
+
+  while (node = queue.shift)
+    # Each node that we visit should be added to the result, so that we end up
+    # with an array of the nodes that we traversed.
+    result << node
+
+    # Iterate over each child node.
+    node.compact_child_nodes.each do |child_node|
+      child_location = child_node.location
+
+      start_line = child_location.start_line
+      end_line = child_location.end_line
+
+      # Here we determine if the given coordinates are contained within the
+      # child node's location.
+      if start_line == end_line
+        if line == start_line && column >= child_location.start_column && column < child_location.end_column
+          queue << child_node
+          break
+        end
+      elsif (line == start_line && column >= child_location.start_column) || (line == end_line && column < child_location.end_column)
+        queue << child_node
+        break
+      elsif line > start_line && line < end_line
+        queue << child_node
+        break
+      end
+    end
+  end
+
+  # Finally, we return the result.
+  result
+end
+
+result = Prism.parse_stream(DATA)
+locate(result.value, line: 4, column: 14).each_with_index do |node, index|
+  location = node.location
+  puts "#{" " * index}#{node.type}@#{location.start_line}:#{location.start_column}-#{location.end_line}:#{location.end_column}"
+end
+
+# =>
+# program_node@1:0-7:3
+#  statements_node@1:0-7:3
+#   module_node@1:0-7:3
+#    statements_node@2:2-6:5
+#     class_node@2:2-6:5
+#      statements_node@3:4-5:7
+#       def_node@3:4-5:7
+#        statements_node@4:6-4:21
+#         call_node@4:6-4:21
+#          call_node@4:6-4:15
+#           arguments_node@4:12-4:15
+#            integer_node@4:12-4:15
+
+__END__
+module Foo
+  class Bar
+    def baz
+      111 + 222 + 333
+    end
+  end
+end