Discard '\n' nodes in C and C++

These are from the preprocessor grammar rules, but they're not useful
for difftastic.

Reported upstream: https://github.com/tree-sitter/tree-sitter-c/issues/97

Closes #180

CHANGELOG.md

@@ -10,6 +10,11 @@ When a file is entirely unchanged, difftastic now shows "no changes"
 even if it successfully parsed. Previously it would only show "no
 syntactic changes".
 
+### Parsing
+
+Fixed an issue in C and C++ where blank lines were highlighted after
+novel preprocessor lines.
+
 ## 0.24 (release 26th March 2022)
 
 ### Diffing

sample_files/compare.expected

@@ -85,6 +85,9 @@ sample_files/ocaml_before.ml sample_files/ocaml_after.ml
 sample_files/outer_delimiter_before.el sample_files/outer_delimiter_after.el
 73130b8572a4f17fa6cf828f74e226ce  -
 
+sample_files/preprocesor_before.h sample_files/preprocesor_after.h
+3e4331cb935cbe735a79ebc43786cd3a  -
+
 sample_files/ruby_before.rb sample_files/ruby_after.rb
 4a9847a91e32ec6afdc2f0b01e28d2d6  -
 

sample_files/preprocesor_after.h

@@ -0,0 +1,4 @@
+#include "foo.h"
+#include "novel.h"
+
+struct Bar {};

sample_files/preprocesor_before.h

@@ -0,0 +1,3 @@
+#include "foo.h"
+
+struct Bar {};

src/tree_sitter_parser.rs

@@ -857,6 +857,14 @@ fn atom_from_cursor<'a>(
     let position = nl_pos.from_offsets(node.start_byte(), node.end_byte());
     let mut content = &src[node.start_byte()..node.end_byte()];
 
+    // The C and C++ grammars have a '\n' node with the
+    // preprocessor. This isn't useful for difftastic, because it's
+    // not visible, but leads us to highlight unchanged lines that
+    // happen to have preceding newline node.
+    if node.kind() == "\n" {
+        return vec![];
+    }
+
     // JSX trims whitespace at the beginning and end of text nodes.
     // TODO: match the exact trimming behaviour used in React.
     //