Handling trailing whitespace in Heredoc

CHANGELOG.md

@@ -15,6 +15,7 @@
 * [#8882](https://github.com/rubocop-hq/rubocop/pull/8882): **(Potentially breaking)** RuboCop assumes that Cop classes do not define new `on_<type>` methods at runtime (e.g. via `extend` in `initialize`). ([@marcandre][])
 * [#7966](https://github.com/rubocop-hq/rubocop/issues/7966): **(Breaking)** Enable all pending cops for RuboCop 1.0. ([@koic][])
 * [#8490](https://github.com/rubocop-hq/rubocop/pull/8490): **(Breaking)** Change logic for cop department name computation. Cops inside deep namespaces (5 or more levels deep) now belong to departments with names that are calculated by joining module names starting from the third one with slashes as separators. For example, cop `Rubocop::Cop::Foo::Bar::Baz` now belongs to `Foo/Bar` department (previously it was `Bar`). ([@dsavochkin][])
+* [#8692](https://github.com/rubocop-hq/rubocop/pull/8692): Default changed to disallow `Layout/TrailingWhitespace` in heredoc. ([@marcandre][])
 
 ## 0.93.1 (2020-10-12)
 
@@ -151,6 +152,7 @@
 * [#8661](https://github.com/rubocop-hq/rubocop/pull/8661): Fix an incorrect auto-correct for `Style/MultilineTernaryOperator` when returning a multiline ternary operator expression. ([@koic][])
 * [#8526](https://github.com/rubocop-hq/rubocop/pull/8526): Fix a false positive for `Style/CaseEquality` cop when the receiver is not a camel cased constant. ([@koic][])
 * [#8673](https://github.com/rubocop-hq/rubocop/issues/8673): Fix the JSON parse error when specifying `--format=json` and `--stdin` options. ([@koic][])
+* [#8692](https://github.com/rubocop-hq/rubocop/pull/8692): Fix `Layout/TrailingWhitespace` auto-correction in heredoc. ([@marcandre][])
 
 ### Changes
 

config/default.yml

@@ -1335,7 +1335,7 @@ Layout/TrailingWhitespace:
   Enabled: true
   VersionAdded: '0.49'
   VersionChanged: '0.83'
-  AllowInHeredoc: true
+  AllowInHeredoc: false
 
 #################### Lint ##################################
 ### Warnings

docs/modules/ROOT/pages/cops_layout.adoc

@@ -6360,7 +6360,7 @@ x = 0
 x = 0
 ----
 
-==== AllowInHeredoc: false
+==== AllowInHeredoc: false (default)
 
 [source,ruby]
 ----
@@ -6369,9 +6369,20 @@ x = 0
 code = <<~RUBY
   x = 0
 RUBY
+
+# ok
+code = <<~RUBY
+  x = 0 #{}
+RUBY
+
+# good
+trailing_whitespace = ' '
+code = <<~RUBY
+  x = 0#{trailing_whitespace}
+RUBY
 ----
 
-==== AllowInHeredoc: true (default)
+==== AllowInHeredoc: true
 
 [source,ruby]
 ----
@@ -6388,7 +6399,7 @@ RUBY
 | Name | Default value | Configurable values
 
 | AllowInHeredoc
-| `true`
+| `false`
 | Boolean
 |===
 

lib/rubocop/cop/layout/trailing_whitespace.rb

@@ -14,14 +14,25 @@ module Layout
       #   # good
       #   x = 0
       #
-      # @example AllowInHeredoc: false
+      # @example AllowInHeredoc: false (default)
       #   # The line in this example contains spaces after the 0.
       #   # bad
       #   code = <<~RUBY
       #     x = 0
       #   RUBY
       #
-      # @example AllowInHeredoc: true (default)
+      #   # ok
+      #   code = <<~RUBY
+      #     x = 0 #{}
+      #   RUBY
+      #
+      #   # good
+      #   trailing_whitespace = ' '
+      #   code = <<~RUBY
+      #     x = 0#{trailing_whitespace}
+      #   RUBY
+      #
+      # @example AllowInHeredoc: true
       #   # The line in this example contains spaces after the 0.
       #   # good
       #   code = <<~RUBY
@@ -35,36 +46,49 @@ class TrailingWhitespace < Base
         MSG = 'Trailing whitespace detected.'
 
         def on_new_investigation
-          heredoc_ranges = extract_heredoc_ranges(processed_source.ast)
+          @heredocs = extract_heredocs(processed_source.ast)
           processed_source.lines.each_with_index do |line, index|
-            lineno = index + 1
-
             next unless line.end_with?(' ', "\t")
-            next if skip_heredoc? && inside_heredoc?(heredoc_ranges, lineno)
 
-            range = offense_range(lineno, line)
-            add_offense(range) do |corrector|
+            process_line(line, index + 1)
+          end
+        end
+
+        private
+
+        def process_line(line, lineno)
+          heredoc = find_heredoc(lineno)
+          return if skip_heredoc? && heredoc
+
+          range = offense_range(lineno, line)
+          add_offense(range) do |corrector|
+            if heredoc
+              corrector.insert_after(range, '#{}') unless static?(heredoc) # rubocop:disable Lint/InterpolationCheck
+            else
               corrector.remove(range)
             end
           end
         end
 
-        private
+        def static?(heredoc)
+          heredoc.loc.expression.source.end_with? "'"
+        end
 
         def skip_heredoc?
           cop_config.fetch('AllowInHeredoc', false)
         end
 
-        def inside_heredoc?(heredoc_ranges, line_number)
-          heredoc_ranges.any? { |r| r.include?(line_number) }
+        def find_heredoc(line_number)
+          @heredocs.each { |node, r| return node if r.include?(line_number) }
+          nil
         end
 
-        def extract_heredoc_ranges(ast)
+        def extract_heredocs(ast)
           return [] unless ast
 
           ast.each_node(:str, :dstr, :xstr).select(&:heredoc?).map do |node|
             body = node.location.heredoc_body
-            (body.first_line...body.last_line)
+            [node, body.first_line...body.last_line]
           end
         end
 

spec/rubocop/cop/layout/trailing_whitespace_spec.rb

@@ -89,4 +89,37 @@
       expect(offenses.size).to eq(1)
     end
   end
+
+  context 'when `AllowInHeredoc` is set to false' do
+    let(:cop_config) { { 'AllowInHeredoc' => false } }
+
+    it 'corrects safely trailing whitespace in a heredoc string' do
+      expect_offense(<<~RUBY)
+        x = <<~EXAMPLE
+          has trailing#{trailing_whitespace}
+                      ^ Trailing whitespace detected.
+          no trailing
+        EXAMPLE
+      RUBY
+
+      expect_correction(<<~RUBY)
+        x = <<~EXAMPLE
+          has trailing \#{}
+          no trailing
+        EXAMPLE
+      RUBY
+    end
+
+    it 'does not correct trailing whitespace in a static heredoc string' do
+      expect_offense(<<~RUBY)
+        x = <<~'EXAMPLE'
+          has trailing#{trailing_whitespace}
+                      ^ Trailing whitespace detected.
+          no trailing
+        EXAMPLE
+      RUBY
+
+      expect_no_corrections
+    end
+  end
 end