rust: add Debug constraint to Matcher trait

This makes sure we can easily debug which Matcher we're looking at when using
trait objects, and is just generally useful. Effort to make the debugging
output nicer has been kept to a minimum, please feel free to improve.

rust/hg-core/src/matchers.rs

@@ -46,7 +46,7 b' pub enum VisitChildrenSet {'
     Recursive,
 }
 
-pub trait Matcher {
+pub trait Matcher: core::fmt::Debug {
     /// Explicitly listed files
     fn file_set(&self) -> Option<&HashSet<HgPathBuf>>;
     /// Returns whether `filename` is in `file_set`
@@ -283,6 +283,18 b" pub struct IncludeMatcher<'a> {"
     parents: HashSet<HgPathBuf>,
 }
 
+impl core::fmt::Debug for IncludeMatcher<'_> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("IncludeMatcher")
+            .field("patterns", &String::from_utf8_lossy(&self.patterns))
+            .field("prefix", &self.prefix)
+            .field("roots", &self.roots)
+            .field("dirs", &self.dirs)
+            .field("parents", &self.parents)
+            .finish()
+    }
+}
+
 impl<'a> Matcher for IncludeMatcher<'a> {
     fn file_set(&self) -> Option<&HashSet<HgPathBuf>> {
         None
@@ -330,6 +342,7 b" impl<'a> Matcher for IncludeMatcher<'a> "
 }
 
 /// The union of multiple matchers. Will match if any of the matchers match.
+#[derive(Debug)]
 pub struct UnionMatcher {
     matchers: Vec<Box<dyn Matcher + Sync>>,
 }
@@ -393,6 +406,7 b' impl UnionMatcher {'
     }
 }
 
+#[derive(Debug)]
 pub struct IntersectionMatcher {
     m1: Box<dyn Matcher + Sync>,
     m2: Box<dyn Matcher + Sync>,
@@ -474,6 +488,7 b' impl IntersectionMatcher {'
     }
 }
 
+#[derive(Debug)]
 pub struct DifferenceMatcher {
     base: Box<dyn Matcher + Sync>,
     excluded: Box<dyn Matcher + Sync>,