A first stab at a pull example. (#427)

A first stab at a pull example.

Author: zaphar

examples/pull.rs

@@ -0,0 +1,208 @@
+/*
+ * libgit2 "pull" example - shows how to pull remote data into a local branch.
+ *
+ * Written by the libgit2 contributors
+ *
+ * To the extent possible under law, the author(s) have dedicated all copyright
+ * and related and neighboring rights to this software to the public domain
+ * worldwide. This software is distributed without any warranty.
+ *
+ * You should have received a copy of the CC0 Public Domain Dedication along
+ * with this software. If not, see
+ * <http://creativecommons.org/publicdomain/zero/1.0/>.
+ */
+
+use git2::Repository;
+use std::io::{self, Write};
+use std::str;
+use structopt::StructOpt;
+
+#[derive(StructOpt)]
+struct Args {
+    arg_remote: Option<String>,
+    arg_branch: Option<String>,
+}
+
+fn do_fetch<'a>(
+    repo: &'a git2::Repository,
+    refs: &[&str],
+    remote: &'a mut git2::Remote,
+) -> Result<git2::AnnotatedCommit<'a>, git2::Error> {
+    let mut cb = git2::RemoteCallbacks::new();
+
+    // Print out our transfer progress.
+    cb.transfer_progress(|stats| {
+        if stats.received_objects() == stats.total_objects() {
+            print!(
+                "Resolving deltas {}/{}\r",
+                stats.indexed_deltas(),
+                stats.total_deltas()
+            );
+        } else if stats.total_objects() > 0 {
+            print!(
+                "Received {}/{} objects ({}) in {} bytes\r",
+                stats.received_objects(),
+                stats.total_objects(),
+                stats.indexed_objects(),
+                stats.received_bytes()
+            );
+        }
+        io::stdout().flush().unwrap();
+        true
+    });
+
+    let mut fo = git2::FetchOptions::new();
+    fo.remote_callbacks(cb);
+    // Always fetch all tags.
+    // Perform a download and also update tips
+    fo.download_tags(git2::AutotagOption::All);
+    println!("Fetching {} for repo", remote.name().unwrap());
+    remote.fetch(refs, Some(&mut fo), None)?;
+
+    // If there are local objects (we got a thin pack), then tell the user
+    // how many objects we saved from having to cross the network.
+    let stats = remote.stats();
+    if stats.local_objects() > 0 {
+        println!(
+            "\rReceived {}/{} objects in {} bytes (used {} local \
+             objects)",
+            stats.indexed_objects(),
+            stats.total_objects(),
+            stats.received_bytes(),
+            stats.local_objects()
+        );
+    } else {
+        println!(
+            "\rReceived {}/{} objects in {} bytes",
+            stats.indexed_objects(),
+            stats.total_objects(),
+            stats.received_bytes()
+        );
+    }
+
+    let fetch_head = repo.find_reference("FETCH_HEAD")?;
+    Ok(repo.reference_to_annotated_commit(&fetch_head)?)
+}
+
+fn fast_forward(
+    repo: &Repository,
+    lb: &mut git2::Reference,
+    rc: &git2::AnnotatedCommit,
+) -> Result<(), git2::Error> {
+    let name = match lb.name() {
+        Some(s) => s.to_string(),
+        None => String::from_utf8_lossy(lb.name_bytes()).to_string(),
+    };
+    let msg = format!("Fast-Forward: Setting {} to id: {}", name, rc.id());
+    println!("{}", msg);
+    lb.set_target(rc.id(), &msg)?;
+    repo.set_head(&name)?;
+    repo.checkout_head(Some(
+        git2::build::CheckoutBuilder::default()
+            // For some reason the force is required to make the working directory actually get updated
+            // I suspect we should be adding some logic to handle dirty working directory states
+            // but this is just an example so maybe not.
+            .force(),
+    ))?;
+    Ok(())
+}
+
+fn normal_merge(
+    repo: &Repository,
+    local: &git2::AnnotatedCommit,
+    remote: &git2::AnnotatedCommit,
+) -> Result<(), git2::Error> {
+    let local_tree = repo.find_commit(local.id())?.tree()?;
+    let remote_tree = repo.find_commit(remote.id())?.tree()?;
+    let ancestor = repo
+        .find_commit(repo.merge_base(local.id(), remote.id())?)?
+        .tree()?;
+    let mut idx = repo.merge_trees(&ancestor, &local_tree, &remote_tree, None)?;
+
+    if idx.has_conflicts() {
+        println!("Merge conficts detected...");
+        repo.checkout_index(Some(&mut idx), None)?;
+        return Ok(());
+    }
+    let result_tree = repo.find_tree(idx.write_tree_to(repo)?)?;
+    // now create the merge commit
+    let msg = format!("Merge: {} into {}", remote.id(), local.id());
+    let sig = repo.signature()?;
+    let local_commit = repo.find_commit(local.id())?;
+    let remote_commit = repo.find_commit(remote.id())?;
+    // Do our merge commit and set current branch head to that commit.
+    let _merge_commit = repo.commit(
+        Some("HEAD"),
+        &sig,
+        &sig,
+        &msg,
+        &result_tree,
+        &[&local_commit, &remote_commit],
+    )?;
+    // Set working tree to match head.
+    repo.checkout_head(None)?;
+    Ok(())
+}
+
+fn do_merge<'a>(
+    repo: &'a Repository,
+    remote_branch: &str,
+    fetch_commit: git2::AnnotatedCommit<'a>,
+) -> Result<(), git2::Error> {
+    // 1. do a merge analysis
+    let analysis = repo.merge_analysis(&[&fetch_commit])?;
+
+    // 2. Do the appopriate merge
+    if analysis.0.is_fast_forward() {
+        println!("Doing a fast forward");
+        // do a fast forward
+        let refname = format!("refs/heads/{}", remote_branch);
+        match repo.find_reference(&refname) {
+            Ok(mut r) => {
+                fast_forward(repo, &mut r, &fetch_commit)?;
+            }
+            Err(_) => {
+                // The branch doesn't exist so just set the reference to the
+                // commit directly. Usually this is because you are pulling
+                // into an empty repository.
+                repo.reference(
+                    &refname,
+                    fetch_commit.id(),
+                    true,
+                    &format!("Setting {} to {}", remote_branch, fetch_commit.id()),
+                )?;
+                repo.set_head(&refname)?;
+                repo.checkout_head(Some(
+                    git2::build::CheckoutBuilder::default()
+                        .allow_conflicts(true)
+                        .conflict_style_merge(true)
+                        .force(),
+                ))?;
+            }
+        };
+    } else if analysis.0.is_normal() {
+        // do a normal merge
+        let head_commit = repo.reference_to_annotated_commit(&repo.head()?)?;
+        normal_merge(&repo, &head_commit, &fetch_commit)?;
+    } else {
+        println!("Nothing to do...");
+    }
+    Ok(())
+}
+
+fn run(args: &Args) -> Result<(), git2::Error> {
+    let remote_name = args.arg_remote.as_ref().map(|s| &s[..]).unwrap_or("origin");
+    let remote_branch = args.arg_branch.as_ref().map(|s| &s[..]).unwrap_or("master");
+    let repo = Repository::open(".")?;
+    let mut remote = repo.find_remote(remote_name)?;
+    let fetch_commit = do_fetch(&repo, &[remote_branch], &mut remote)?;
+    do_merge(&repo, &remote_branch, fetch_commit)
+}
+
+fn main() {
+    let args = Args::from_args();
+    match run(&args) {
+        Ok(()) => {}
+        Err(e) => println!("error: {}", e),
+    }
+}