Support checking out the previous MR by using - instead of an MR number.

Author: arusahni

src/git.rs

@@ -1,7 +1,8 @@
 use anyhow::{anyhow, Result};
-use std::collections::HashSet;
+use logchop::OptionLogger;
 use std::path::Path;
 use std::str;
+use std::{collections::HashSet, convert::TryInto};
 
 use duct::cmd;
 use git2::{Config, Repository};
@@ -138,13 +139,50 @@ pub fn guess_default_remote_name() -> Result<String> {
     }
 }
 
+/// Get the ID of the previous MR that had been checked out using git-req
+pub fn get_previous_mr_id() -> Result<i64> {
+    let repo = Repository::open_from_env().expect("Couldn't find repository");
+    let testco = repo.find_reference("git-req/previous")?;
+    let content = testco.peel_to_blob()?;
+    let binary = content.content();
+    let reqnum = i64::from_le_bytes(binary.try_into()?);
+    debug!("Loaded previous reference MR number: {}", reqnum);
+    Ok(reqnum)
+}
+
+/// Push a new `current` history ref, moving the existing `current` to `previous`
+pub fn push_current_ref(new_req_number: i64) -> Result<i64> {
+    trace!("Storing refs for MR {}", new_req_number);
+    let repo = Repository::open_from_env().expect("Couldn't find repository");
+    let old_oid = match repo.find_reference("git-req/current") {
+        Ok(current_ref) => current_ref
+            .target()
+            .debug_none("Could not peel current ref"),
+        Err(_) => None,
+    };
+    let data = new_req_number.to_le_bytes();
+    let new_oid = repo.blob(&data).unwrap();
+    if let Some(oid) = old_oid {
+        repo.reference("git-req/previous", oid, true, "").unwrap();
+        debug!("Wrote old OID '{}' to git_req/previous", oid);
+    };
+    repo.reference("git-req/current", new_oid, true, "")?;
+    Ok(new_req_number)
+}
+
+#[derive(Debug)]
+pub enum CheckoutResult {
+    BranchChanged,
+    BranchUnchanged,
+}
+
 /// Check out a branch by name
 pub fn checkout_branch(
     remote_name: &str,
     remote_branch_name: &str,
     local_branch_name: &str,
     is_virtual_remote_branch: bool,
-) -> Result<()> {
+) -> Result<CheckoutResult> {
     let repo = Repository::open_from_env().expect("Couldn't find repository");
     let local_branch_name = match get_project_config("defaultremote") {
         Some(default_remote_name) => {
@@ -166,8 +204,16 @@ pub fn checkout_branch(
     match local_branch_exists {
         Ok(_) => {
             debug!("Checking out branch: {}", local_branch_name);
+            let head = repo.head()?;
+            trace!("On head: {:?}", head.name());
+            if head.is_branch()
+                && head.name().unwrap() == format!("refs/heads/{}", &local_branch_name)
+            {
+                // return Err(anyhow!("Already on {}", &local_branch_name));
+                return Ok(CheckoutResult::BranchUnchanged);
+            }
             match cmd!("git", "checkout", &local_branch_name).run() {
-                Ok(_) => Ok(()),
+                Ok(_) => Ok(CheckoutResult::BranchChanged),
                 Err(err) => Err(anyhow!("Could not check out local branch: {}", err)),
             }
         }
@@ -203,7 +249,7 @@ pub fn checkout_branch(
                 );
             };
             match cmd("git", checkout_args).run() {
-                Ok(_) => Ok(()),
+                Ok(_) => Ok(CheckoutResult::BranchChanged),
                 Err(err) => Err(anyhow!("Could not check out local branch: {}", err)),
             }
         }

src/main.rs

@@ -8,7 +8,6 @@ use colored::*;
 use git2::ErrorCode;
 use lazy_static::lazy_static;
 use log::{debug, error, info, trace};
-use logchop::*;
 use std::io::{self, stdin, stdout, Cursor, Write};
 use std::{env, include_str, process};
 use tabwriter::TabWriter;
@@ -58,20 +57,27 @@ fn checkout_mr(remote_name: &str, mr_id: i64) {
         abort(&message);
     });
     debug!("Got remote branch name: {}", remote_branch_name);
-    git::checkout_branch(
+    match git::checkout_branch(
         remote_name,
         &remote_branch_name,
         &remote.get_local_req_branch(mr_id).unwrap(),
         remote.has_virtual_remote_branch_names(),
     )
-    .info_ok("Done")
     .unwrap_or_else(|err| {
-        eprintln!(
-            "{}",
-            format!("There was an error checking out the branch: {}", err).red()
-        );
-        process::exit(1)
-    });
+        let message = format!("There was an error checking out the branch: {}", err);
+        abort(&message);
+    }) {
+        git::CheckoutResult::BranchChanged => {
+            if git::push_current_ref(mr_id).is_err() {
+                trace!("Couldn't update the current ref");
+                eprintln!("{}", "failed to update some git-req metadata".yellow());
+            }
+        }
+        _ => {
+            eprintln!("Already on branch");
+        }
+    };
+    trace!("Done");
 }
 
 /// Clear the API key for the current domain
@@ -229,14 +235,18 @@ fn main() {
         app = build_cli();
         generate_completion(&mut app, &shell_name);
     } else {
-        match matches.value_of("REQUEST_ID").unwrap().parse() {
-            Ok(mr_id) => {
-                checkout_mr(&get_remote_name(&matches), mr_id);
-            }
-            Err(_) => {
-                eprintln!("{}", "Invalid request ID provided".red());
-                process::exit(1);
-            }
+        let request_id = matches.value_of("REQUEST_ID").unwrap();
+        let mr_id = if request_id == "-" {
+            trace!("Received request for previous MR");
+            git::get_previous_mr_id().unwrap_or_else(|_| {
+                abort("Could not find previous request");
+            })
+        } else {
+            trace!("Received request for numbered MR: {}", request_id);
+            request_id.parse::<i64>().unwrap_or_else(|_| {
+                abort("Invalid request ID provided");
+            })
         };
+        checkout_mr(&get_remote_name(&matches), mr_id);
     }
 }