[ruby/syntax_suggest] Fix

https://github.com/ruby/syntax_suggest/pull/187 Handle if/else with
empty/comment
line

Reported in #187 this code:

```
class Foo
  def foo
    if cond?
      foo
    else
      # comment
    end
  end

  # ...

  def bar
    if @recv
    end_is_missing_here
  end
end
```

Triggers an incorrect suggestion:

```
Unmatched keyword, missing `end' ?
   1  class Foo
   2    def foo
>  3      if cond?
>  5      else
   8    end
  16  end
```

Part of the issue is that while scanning we're using newlines to determine when to stop and pause. This is useful for determining logically smaller chunks to evaluate but in this case it causes us to pause before grabbing the "end" that is right below the newline. This problem is similar to https://github.com/ruby/syntax_suggest/pull/179.

However in the case of expanding same indentation "neighbors" I want to always grab all empty values at the end of the scan. I don't want to do that when changing indentation levels as it affects scan results.

There may be some way to normalize this behavior between the two, but the tests really don't like that change.

To fix this issue for expanding against different indentation I needed a way to first try and grab any additional newlines with the ability to rollback that guess. In #192 I experimented with decoupling scanning from the AroundBlockScan logic. It also added the ability to take a snapshot of the current scanner and rollback to prior changes.

With this ability in place now we:

- Grab extra empties before looking at the above/below line for the matching keyword/end statement
- If there's a match, grab it
- If there's no match, discard the newlines we picked up in the evaluation

That solves the issue.

https://github.com/ruby/syntax_suggest/commit/513646b912

1 files changed, 31 insertions, 0 deletions

diff --git a/spec/syntax_suggest/integration/syntax_suggest_spec.rb b/spec/syntax_suggest/integration/syntax_suggest_spec.rb
index e701287985..64dafabcdd 100644
--- a/spec/syntax_suggest/integration/syntax_suggest_spec.rb
+++ b/spec/syntax_suggest/integration/syntax_suggest_spec.rb
@@ -204,5 +204,36 @@ module SyntaxSuggest
         > 4  end
       EOM
     end
+
+    it "empty else" do
+      source = <<~'EOM'
+        class Foo
+          def foo
+            if cond?
+              foo
+            else
+
+            end
+          end
+
+          # ...
+
+          def bar
+            if @recv
+            end_is_missing_here
+          end
+        end
+      EOM
+
+      io = StringIO.new
+      SyntaxSuggest.call(
+        io: io,
+        source: source
+      )
+      out = io.string
+      expect(out).to include(<<~EOM)
+        end_is_missing_here
+      EOM
+    end
   end
 end