fix: assure empty paths are always matching a Search

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

Author: Byron

gix-pathspec/src/search/matching.rs

@@ -31,6 +31,21 @@ impl Search {
         is_dir: Option<bool>,
         attributes: &mut dyn FnMut(&BStr, Case, bool, &mut gix_attributes::search::Outcome) -> bool,
     ) -> Option<Match<'_>> {
+        static MATCH_ALL_STAND_IN: Pattern = Pattern {
+            path: BString::new(Vec::new()),
+            signature: MagicSignature::empty(),
+            search_mode: SearchMode::ShellGlob,
+            attributes: Vec::new(),
+            prefix_len: 0,
+            nil: true,
+        };
+        if relative_path.is_empty() {
+            return Some(Match {
+                pattern: &MATCH_ALL_STAND_IN,
+                sequence_number: 0,
+                kind: Always,
+            });
+        }
         let basename_not_important = None;
         if relative_path
             .get(..self.common_prefix_len)
@@ -106,14 +121,6 @@ impl Search {
         });
 
         if res.is_none() && self.all_patterns_are_excluded {
-            static MATCH_ALL_STAND_IN: Pattern = Pattern {
-                path: BString::new(Vec::new()),
-                signature: MagicSignature::empty(),
-                search_mode: SearchMode::ShellGlob,
-                attributes: Vec::new(),
-                prefix_len: 0,
-                nil: true,
-            };
             Some(Match {
                 pattern: &MATCH_ALL_STAND_IN,
                 sequence_number: patterns_len,
@@ -133,7 +140,7 @@ 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 +201,7 @@ 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 +57,31 @@ 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 mut search = gix_pathspec::Search::from_specs(pathspecs(specs), None, Path::new(""))?;
+        assert_eq!(
+            search
+                .pattern_matching_relative_path("".into(), None, &mut no_attrs)
+                .map(|m| m.kind),
+            Some(Always),
+            "{specs:?}"
+        );
+        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(""))?;