Reduce amount of max candidates, add --debug flag (#298)

git-repository/src/commit.rs

@@ -24,6 +24,22 @@ pub mod describe {
     use git_odb::FindExt;
     use std::borrow::Cow;
 
+    /// The result of [try_resolve()][Platform::try_resolve()].
+    pub struct Resolution<'repo> {
+        /// The outcome of the describe operation.
+        pub outcome: git_revision::describe::Outcome<'static>,
+        /// The id to describe.
+        pub id: crate::Id<'repo>,
+    }
+
+    impl<'repo> Resolution<'repo> {
+        /// Turn this instance into something displayable
+        pub fn format(self) -> Result<git_revision::describe::Format<'static>, Error> {
+            let prefix = self.id.shorten()?;
+            Ok(self.outcome.into_format(prefix.hex_len()))
+        }
+    }
+
     /// The error returned by [try_format()][Platform::try_format()].
     #[derive(Debug, thiserror::Error)]
     #[allow(missing_docs)]
@@ -126,6 +142,14 @@ pub mod describe {
         ///
         /// Note that there will always be `Some(format)`
         pub fn try_format(self) -> Result<Option<git_revision::describe::Format<'static>>, Error> {
+            Ok(self.try_resolve()?.map(|r| r.format()).transpose()?)
+        }
+
+        /// Try to find a name for the configured commit id using all prior configuration, returning `Some(Outcome)`
+        /// if one was found.
+        ///
+        /// The outcome provides additional information, but leaves the caller with the burden
+        pub fn try_resolve(self) -> Result<Option<crate::commit::describe::Resolution<'repo>>, Error> {
             // TODO: dirty suffix with respective dirty-detection
             let outcome = git_revision::describe(
                 &self.id,
@@ -137,8 +161,11 @@ pub mod describe {
                     ..Default::default()
                 },
             )?;
-            let prefix = self.id.attach(self.repo).shorten()?;
-            Ok(outcome.map(|o| o.into_format(prefix.hex_len())))
+
+            Ok(outcome.map(|outcome| crate::commit::describe::Resolution {
+                outcome,
+                id: self.id.attach(self.repo),
+            }))
         }
 
         /// Like [`try_format()`][Platform::try_format()], but turns `id_as_fallback()` on to always produce a format.

git-revision/src/describe.rs

@@ -19,6 +19,8 @@ pub struct Outcome<'name> {
     pub depth: u32,
     /// The mapping between object ids and their names initially provided by the describe call.
     pub name_by_oid: hash_hasher::HashedMap<git_hash::ObjectId, Cow<'name, BStr>>,
+    /// The amount of commits we traversed.
+    pub commits_seen: u32,
 }
 
 impl<'a> Outcome<'a> {
@@ -115,7 +117,7 @@ pub struct Options<'name> {
 impl<'name> Default for Options<'name> {
     fn default() -> Self {
         Options {
-            max_candidates: MAX_CANDIDATES,
+            max_candidates: 28, // the same number as git uses, otherwise we perform worse by default on big repos
             name_by_oid: Default::default(),
             fallback_to_oid: false,
             first_parent: false,
@@ -182,6 +184,7 @@ pub(crate) mod function {
                 id: commit.to_owned(),
                 depth: 0,
                 name_by_oid,
+                commits_seen: 0,
             }));
         }
         max_candidates = max_candidates.min(MAX_CANDIDATES);
@@ -192,19 +195,19 @@ pub(crate) mod function {
 
         let mut queue = VecDeque::from_iter(Some(commit.to_owned()));
         let mut candidates = Vec::new();
-        let mut seen_commits = 0;
+        let mut commits_seen = 0;
         let mut gave_up_on_commit = None;
         let mut seen = hash_hasher::HashedMap::default();
         seen.insert(commit.to_owned(), 0u32);
 
         while let Some(commit) = queue.pop_front() {
-            seen_commits += 1;
+            commits_seen += 1;
             if let Some(name) = name_by_oid.get(&commit) {
                 if candidates.len() < max_candidates {
                     let identity_bit = 1 << candidates.len();
                     candidates.push(Candidate {
                         name: name.clone(),
-                        commits_in_its_future: seen_commits - 1,
+                        commits_in_its_future: commits_seen - 1,
                         identity_bit,
                         order: candidates.len(),
                     });
@@ -266,6 +269,7 @@ pub(crate) mod function {
                     name: None,
                     name_by_oid,
                     depth: 0,
+                    commits_seen,
                 }))
             } else {
                 Ok(None)
@@ -280,9 +284,10 @@ pub(crate) mod function {
 
         if let Some(commit_id) = gave_up_on_commit {
             queue.push_front(commit_id);
+            commits_seen -= 1;
         }
 
-        finish_depth_computation(
+        commits_seen += finish_depth_computation(
             queue,
             find,
             candidates.first_mut().expect("at least one candidate"),
@@ -298,6 +303,7 @@ pub(crate) mod function {
             id: commit.to_owned(),
             depth: c.commits_in_its_future,
             name_by_oid,
+            commits_seen,
         }))
     }
 
@@ -368,12 +374,14 @@ pub(crate) mod function {
         mut parent_buf: Vec<u8>,
         mut parents: Vec<(git_hash::ObjectId, Flags)>,
         first_parent: bool,
-    ) -> Result<(), Error<E>>
+    ) -> Result<u32, Error<E>>
     where
         Find: for<'b> FnMut(&oid, &'b mut Vec<u8>) -> Result<CommitRefIter<'b>, E>,
         E: std::error::Error + Send + Sync + 'static,
     {
+        let mut commits_seen = 0;
         while let Some(commit) = queue.pop_front() {
+            commits_seen += 1;
             let flags = seen[&commit];
             if (flags & best_candidate.identity_bit) == best_candidate.identity_bit {
                 if queue
@@ -398,7 +406,7 @@ pub(crate) mod function {
                 first_parent,
             )?;
         }
-        Ok(())
+        Ok(commits_seen)
     }
 
     #[derive(Debug)]

git-revision/src/lib.rs

@@ -2,7 +2,7 @@
 //!
 //! One can also describe revisions using a different algorithm.
 #![forbid(unsafe_code, rust_2018_idioms)]
-#[deny(missing_docs)]
+#![deny(missing_docs)]
 
 /// Access to collections optimized for keys that are already a hash.
 pub use hash_hasher;

git-revision/tests/describe/format.rs

@@ -11,6 +11,7 @@ fn exact_match_with_dirty_and_long() {
         id: hex_to_id("b920bbb055e1efb9080592a409d3975738b6efb3"),
         depth: 0,
         name_by_oid: Default::default(),
+        commits_seen: 0,
     }
     .into_format(7);
     assert!(format.is_exact_match());
@@ -38,6 +39,7 @@ fn show_abbrev_hash_if_no_name_is_known() {
         id: hex_to_id("b920bbb055e1efb9080592a409d3975738b6efb3"),
         depth: 0,
         name_by_oid: Default::default(),
+        commits_seen: 0,
     }
     .into_format(7);
     assert!(

gitoxide-core/src/repository/commit.rs

@@ -6,11 +6,13 @@ pub fn describe(
     repo: impl Into<PathBuf>,
     rev_spec: Option<&str>,
     mut out: impl std::io::Write,
+    mut err: impl std::io::Write,
     describe::Options {
         all_tags,
         all_refs,
         first_parent,
         always,
+        statistics,
         long_format,
     }: describe::Options,
 ) -> Result<()> {
@@ -27,14 +29,19 @@ pub fn describe(
     } else {
         Default::default()
     };
-    let mut describe_id = commit
+    let resolution = commit
         .describe()
         .names(select_ref)
         .traverse_first_parent(first_parent)
         .id_as_fallback(always)
-        .try_format()?
+        .try_resolve()?
         .with_context(|| format!("Did not find a single candidate ref for naming id '{}'", commit.id))?;
 
+    if statistics {
+        writeln!(err, "traversed {} commits", resolution.outcome.commits_seen)?;
+    }
+
+    let mut describe_id = resolution.format()?;
     describe_id.long(long_format);
 
     writeln!(out, "{}", describe_id)?;
@@ -49,5 +56,6 @@ pub mod describe {
         pub first_parent: bool,
         pub always: bool,
         pub long_format: bool,
+        pub statistics: bool,
     }
 }

src/plumbing/main.rs

@@ -9,6 +9,7 @@ use std::{
 
 use anyhow::Result;
 use clap::Parser;
+
 use gitoxide_core as core;
 use gitoxide_core::pack::verify;
 
@@ -163,23 +164,26 @@ pub fn main() -> Result<()> {
                     first_parent,
                     always,
                     long,
+                    statistics,
                     rev_spec,
                 } => prepare_and_run(
                     "repository-commit-describe",
                     verbose,
                     progress,
                     progress_keep_open,
                     None,
-                    move |_progress, out, _err| {
+                    move |_progress, out, err| {
                         core::repository::commit::describe(
                             repository,
                             rev_spec.as_deref(),
                             out,
+                            err,
                             core::repository::commit::describe::Options {
                                 all_tags,
                                 all_refs,
                                 long_format: long,
                                 first_parent,
+                                statistics,
                                 always,
                             },
                         )

src/plumbing/options.rs

@@ -411,6 +411,10 @@ pub mod repo {
                 #[clap(long, short = 'l')]
                 long: bool,
 
+                /// Print information on stderr to inform about performance statistics
+                #[clap(long, short = 's')]
+                statistics: bool,
+
                 #[clap(long)]
                 /// If there was no way to describe the commit, fallback to using the abbreviated input revision.
                 always: bool,