Patchwork D11722: rhg: implement the rhg-debugignore subcommand

diff --git a/rust/rhg/src/main.rs b/rust/rhg/src/main.rs
--- a/rust/rhg/src/main.rs
+++ b/rust/rhg/src/main.rs
@@ -434,6 +434,7 @@ 
     cat
     debugdata
     debugrequirements
+    debugignorerhg
     files
     root
     config
diff --git a/rust/rhg/src/commands/debugignorerhg.rs b/rust/rhg/src/commands/debugignorerhg.rs
new file mode 100644
--- /dev/null
+++ b/rust/rhg/src/commands/debugignorerhg.rs
@@ -0,0 +1,39 @@ 
+
+use crate::error::CommandError;
+use clap::{SubCommand};
+use hg;
+use hg::matchers::get_ignore_matcher;
+use hg::StatusError;
+use log::{warn};
+
+pub const HELP_TEXT: &str = "
+Show effective hgignore patterns used by rhg.
+
+This is a pure Rust version of `hg debugignore`.
+
+Some options might be missing, check the list below.
+";
+
+pub fn args() -> clap::App<'static, 'static> {
+    SubCommand::with_name("debugignorerhg").about(HELP_TEXT)
+}
+
+pub fn run(invocation: &crate::CliInvocation) -> Result<(), CommandError> {
+    let repo = invocation.repo?;
+
+    let ignore_file = repo.working_directory_vfs().join(".hgignore"); // TODO hardcoded
+
+    let (ignore_matcher, warnings) = get_ignore_matcher(
+        vec![ignore_file],
+        &repo.working_directory_path().to_owned(),
+        &mut |_pattern_bytes| (),
+    ).map_err(|e| StatusError::from(e))?;
+
+    if !warnings.is_empty() {
+        warn!("Pattern warnings: {:?}", &warnings);
+    }
+
+    let patterns = ignore_matcher.debug_get_patterns();
+    println!("{}", String::from_utf8_lossy(patterns));
+    Ok (())
+}
diff --git a/rust/hg-core/src/matchers.rs b/rust/hg-core/src/matchers.rs
--- a/rust/hg-core/src/matchers.rs
+++ b/rust/hg-core/src/matchers.rs
@@ -560,14 +560,11 @@ 
 /// Parses all "ignore" files with their recursive includes and returns a
 /// function that checks whether a given file (in the general sense) should be
 /// ignored.
-pub fn get_ignore_function<'a>(
+pub fn get_ignore_matcher<'a>(
     mut all_pattern_files: Vec<PathBuf>,
     root_dir: &Path,
     inspect_pattern_bytes: &mut impl FnMut(&[u8]),
-) -> PatternResult<(
-    Box<dyn for<'r> Fn(&'r HgPath) -> bool + Sync + 'a>,
-    Vec<PatternFileWarning>,
-)> {
+) -> PatternResult<(IncludeMatcher<'a>, Vec<PatternFileWarning>)> {
     let mut all_patterns = vec![];
     let mut all_warnings = vec![];
 
@@ -590,10 +587,28 @@ 
         all_warnings.extend(warnings);
     }
     let matcher = IncludeMatcher::new(all_patterns)?;
-    Ok((
-        Box::new(move |path: &HgPath| matcher.matches(path)),
-        all_warnings,
-    ))
+    Ok((matcher, all_warnings))
+}
+
+/// Parses all "ignore" files with their recursive includes and returns a
+/// function that checks whether a given file (in the general sense) should be
+/// ignored.
+pub fn get_ignore_function<'a>(
+    all_pattern_files: Vec<PathBuf>,
+    root_dir: &Path,
+    inspect_pattern_bytes: &mut impl FnMut(&[u8]),
+) -> PatternResult<(
+    Box<dyn for<'r> Fn(&'r HgPath) -> bool + Sync + 'a>,
+    Vec<PatternFileWarning>,
+)> {
+    let res =
+        get_ignore_matcher(all_pattern_files, root_dir, inspect_pattern_bytes);
+    res.map(|(matcher, all_warnings)| {
+        let res: Box<dyn for<'r> Fn(&'r HgPath) -> bool + Sync + 'a> =
+            Box::new(move |path: &HgPath| matcher.matches(path));
+
+        (res, all_warnings)
+    })
 }
 
 impl<'a> IncludeMatcher<'a> {
@@ -628,6 +643,10 @@ 
             .chain(self.parents.iter());
         DirsChildrenMultiset::new(thing, Some(&self.parents))
     }
+
+    pub fn debug_get_patterns(&self) -> &[u8] {
+        self.patterns.as_ref()
+    }
 }
 
 impl<'a> Display for IncludeMatcher<'a> {