ignore: fix gitignore parsing bug for trailing \/

When a glob pattern ended with a \/, and since we permit backslash
escapes, the glob parser gave a "dangling escape" error. Which is weird,
because the \ is clearly not dangling.

The issue is that the layer above the glob parser, the gitignore parser,
was stripping the trailing / so that it wouldn't be part of the matching
logic. Of course, stripping the trailing / while it is escaped without
removing the backslash escape is wrong. So we do that here.

Fixes #2236

3 files changed, 19 insertions, 6 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ba427f92..1e11a8ea 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,5 @@
-13.0.1
-======
+TBD
+===
 Unreleased changes. Release notes have not yet been written.
 
 Bug fixes:
@@ -8,6 +8,8 @@ Bug fixes:
   Fix bug when using `-w` with a regex that can match the empty string.
 * [BUG #1911](https://github.com/BurntSushi/ripgrep/issues/1911):
   Disable mmap searching in all non-64-bit environments.
+* [BUG #2236](https://github.com/BurntSushi/ripgrep/issues/2236):
+  Fix gitignore parsing bug where a trailing `\/` resulted in an error.
 
 
 13.0.0 (2021-06-12)
diff --git a/crates/ignore/src/gitignore.rs b/crates/ignore/src/gitignore.rs
index 7922651c..3c7ba5e6 100644
--- a/crates/ignore/src/gitignore.rs
+++ b/crates/ignore/src/gitignore.rs
@@ -474,10 +474,13 @@ impl GitignoreBuilder {
         }
         // If it ends with a slash, then this should only match directories,
         // but the slash should otherwise not be used while globbing.
-        if let Some((i, c)) = line.char_indices().rev().nth(0) {
-            if c == '/' {
-                glob.is_only_dir = true;
-                line = &line[..i];
+        if line.as_bytes().last() == Some(&b'/') {
+            glob.is_only_dir = true;
+            line = &line[..line.len() - 1];
+            // If the slash was escaped, then remove the escape.
+            // See: https://github.com/BurntSushi/ripgrep/issues/2236
+            if line.as_bytes().last() == Some(&b'\\') {
+                line = &line[..line.len() - 1];
             }
         }
         glob.actual = line.to_string();
diff --git a/tests/regression.rs b/tests/regression.rs
index f777ed1c..e2c56968 100644
--- a/tests/regression.rs
+++ b/tests/regression.rs
@@ -1118,3 +1118,11 @@ pipc () {  # [-h] [-U|-u <pkgspec>[,<pkgspec>...]] [<reqs-in>...] [-- <pip-compi
     let expected = " [-h] [-U|-u <pkgspec>[,<pkgspec>...]] [<reqs-in>...] [-- <pip-compile-arg>...]\n";
     eqnice!(expected, cmd.stdout());
 });
+
+// See: https://github.com/BurntSushi/ripgrep/issues/2236
+rgtest!(r2236, |dir: Dir, mut cmd: TestCommand| {
+    dir.create(".ignore", r"foo\/");
+    dir.create_dir("foo");
+    dir.create("foo/bar", "test\n");
+    cmd.args(&["test"]).assert_err();
+});