NodePattern: Allow comments

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 * [#70](https://github.com/rubocop-hq/rubocop-ast/pull/70): Add `NextNode` ([@marcandre][])
 * [#85](https://github.com/rubocop-hq/rubocop-ast/pull/85): Add `IntNode#value` and `FloatNode#value`. ([@fatkodima][])
+* [#82](https://github.com/rubocop-hq/rubocop-ast/pull/82): `NodePattern`: Allow comments ([@marcandre][])
 
 ### Bug fixes
 

docs/modules/ROOT/pages/node_pattern.adoc

@@ -477,6 +477,22 @@ def_node_matcher :interesting_call?, '(send _ %SOME_CALLS ...)'
 
 Constants as arguments to custom methods are also supported.
 
+== Comments
+
+You may have comments in node patterns at the end of lines
+by preceeding them with `'# '`:
+
+[source,ruby]
+----
+def_node_matcher :complex_stuff, <<~PATTERN
+  (send
+    {#global_const?(:Kernel) nil?}  # check for explicit call like Kernel.p too
+    {:p :pp}                        # let's consider `pp` also
+    $...                            # capture all arguments
+  )
+PATTERN
+----
+
 == `nil` or `nil?`
 
 Take a special attention to nil behavior:

lib/rubocop/ast/node_pattern.rb

@@ -99,6 +99,7 @@ module AST
     #                         # These arguments can be patterns themselves, in
     #                         # which case a matcher responding to === will be
     #                         # passed.
+    #     '# comment'         # comments are accepted at the end of lines
     #
     # You can nest arbitrarily deep:
     #
@@ -122,6 +123,8 @@ class NodePattern
       class Compiler
         SYMBOL       = %r{:(?:[\w+@*/?!<>=~|%^-]+|\[\]=?)}.freeze
         IDENTIFIER   = /[a-zA-Z_][a-zA-Z0-9_-]*/.freeze
+        COMMENT      = /#\s.*$/.freeze
+
         META         = Regexp.union(
           %w"( ) { } [ ] $< < > $... $ ! ^ ` ... + * ?"
         ).freeze
@@ -788,7 +791,7 @@ def substitute_cur_node(code, cur_node, first_cur_node: cur_node)
         end
 
         def self.tokens(pattern)
-          pattern.scan(TOKEN).grep_v(ONLY_SEPARATOR)
+          pattern.gsub(COMMENT, '').scan(TOKEN).grep_v(ONLY_SEPARATOR)
         end
 
         # This method minimizes the closure for our method

spec/rubocop/ast/node_pattern_spec.rb

@@ -1889,6 +1889,14 @@ def withargs(foo, bar, qux)
     end
   end
 
+  describe 'comments' do
+    let(:pattern) { "(int # We want an int\n$_) # Let's capture the value" }
+    let(:ruby) { '42' }
+    let(:captured_val) { 42 }
+
+    it_behaves_like 'single capture'
+  end
+
   describe '.descend' do
     let(:ruby) { '[[1, 2], 3]' }