fix: assure empty paths are always matching a Search

This improvement was triggered by [this question](rust-lang/cargo#13777 (review)).

gix-pathspec/src/search/matching.rs

@@ -133,7 +133,7 @@ impl Search {
     /// is ignored.
     /// Returns `false` if this pathspec has no chance of ever matching `relative_path`.
     pub fn can_match_relative_path(&self, relative_path: &BStr, is_dir: Option<bool>) -> bool {
-        if self.patterns.is_empty() {
+        if self.patterns.is_empty() || relative_path.is_empty() {
             return true;
         }
         let common_prefix_len = self.common_prefix_len.min(relative_path.len());
@@ -194,7 +194,7 @@ impl Search {
     /// When `leading` is `true`, then `d` matches `d/d` as well. Thus, `relative_path` must may be
     /// partially included in `pathspec`, otherwise it has to be fully included.
     pub fn directory_matches_prefix(&self, relative_path: &BStr, leading: bool) -> bool {
-        if self.patterns.is_empty() {
+        if self.patterns.is_empty() || relative_path.is_empty() {
             return true;
         }
         let common_prefix_len = self.common_prefix_len.min(relative_path.len());

gix-pathspec/tests/search/mod.rs

@@ -57,6 +57,24 @@ fn directory_matches_prefix_starting_wildcards_always_match() -> crate::Result {
     Ok(())
 }
 
+#[test]
+fn empty_dir_always_matches() -> crate::Result {
+    for specs in [
+        &["*ir"] as &[_],
+        &[],
+        &["included", ":!excluded"],
+        &[":!all", ":!excluded"],
+    ] {
+        let search = gix_pathspec::Search::from_specs(pathspecs(specs), None, Path::new(""))?;
+        assert!(search.directory_matches_prefix("".into(), false));
+        assert!(search.directory_matches_prefix("".into(), false));
+        for is_dir in [Some(true), Some(false), None] {
+            assert!(search.can_match_relative_path("".into(), is_dir));
+        }
+    }
+    Ok(())
+}
+
 #[test]
 fn directory_matches_prefix_leading() -> crate::Result {
     let search = gix_pathspec::Search::from_specs(pathspecs(&["d/d/generated/b"]), None, Path::new(""))?;