Account for RUST_SRC_URL var at runtime

Author: tesuji

TUTORIAL.md

@@ -17,10 +17,13 @@ or (to avoid cloning rustc)
 RUST_SRC_REPO=/path/to/rust cargo install cargo-bisect-rustc
 ```
 
-The `RUST_SRC_REPO` should be a path to a git clone of the rust repo. If you
-don't specify it, it will look in the current directory for `rust.git` or
-check it out automatically if it's not there (only necessary if doing git hash
-bisections).
+The `RUST_SRC_REPO` should be a path to a git clone of the rust repo.
+The current order how `cargo-bisect-rustc` finds Rust repository path is:
+* `RUST_SRC_REPO` at runtime.
+* `rust.git` in current dir at runtime.
+* `RUST_SRC_REPO` that was set at compilation time.
+* Clone https://github.com/rust-lang/rust automatically
+  (only necessary if doing git hash bisections).
 
 First, if you have a nightly version of the compiler already installed
 as the default toolchain and you don't pass an end flag, the tool is
@@ -40,11 +43,6 @@ So, there's a bunch of ways to run the tool, the easiest one is to
 allow the tool to do the job and just run `cargo bisect-rustc` on the
 project and let the tool figure things out.
 
-Note: you can also pass `RUST_SRC_REPO` env var, should be a path to a
-git clone of the rust repo. If you don't specify it, it will look in the
-current directory for `rust.git` or check it out automatically if it's
-not there (only necessary if doing git hash bisections).
-
 ## Finding a regression
 
 Create a cargo project that demonstrates the regression. Let's use
@@ -134,7 +132,7 @@ d75458200516f06455d175adc001fd993d674050 bors Sat Jul 28 16:44:21 2018 +0000
 ```
 
 and we can, for example, pick the last commit on the day before the nightly,
-`6323d9a45bdf0ac2a9319a6a558537e0a7e6abd1`, as the start of the range, and the 
+`6323d9a45bdf0ac2a9319a6a558537e0a7e6abd1`, as the start of the range, and the
 last commit on the day of the nightly, `866a713258915e6cbb212d135f751a6a8c9e1c0a`,
 as the end of the range.
 

src/git.rs

@@ -3,6 +3,7 @@
 const RUST_SRC_URL: &str = "https://github.com/rust-lang/rust";
 const RUST_SRC_REPO: Option<&str> = option_env!("RUST_SRC_REPO");
 
+use std::env;
 use std::path::Path;
 
 use chrono::{TimeZone, Utc};
@@ -32,26 +33,27 @@ fn lookup_rev<'rev>(repo: &'rev Repository, rev: &str) -> Result<Git2Commit<'rev
 }
 
 fn get_repo() -> Result<Repository, Error> {
-    let loc = Path::new("rust.git");
-    match (RUST_SRC_REPO, loc.exists()) {
-        (Some(_), _) | (_, true) => {
-            let path = RUST_SRC_REPO.map(Path::new).unwrap_or(loc);
-            eprintln!("opening existing repository at {:?}", path);
-            let repo = Repository::open(path)?;
-            {
-                eprintln!("refreshing repository");
-                let mut remote = repo
-                    .find_remote("origin")
-                    .or_else(|_| repo.remote_anonymous("origin"))?;
-                remote.fetch(&["master"], None, None)?;
-            }
-            Ok(repo)
+    fn open(repo: &Path) -> Result<Repository, Error> {
+        eprintln!("opening existing repository at {:?}", repo);
+        let repo = Repository::open(repo)?;
+        {
+            eprintln!("refreshing repository");
+            let mut remote = repo
+                .find_remote("origin")
+                .or_else(|_| repo.remote_anonymous("origin"))?;
+            remote.fetch(&["master"], None, None)?;
         }
-        (None, false) => {
+        Ok(repo)
+    }
+
+    let loc = Path::new("rust.git");
+    match (env::var_os("RUST_SRC_REPO"), RUST_SRC_REPO) {
+        (Some(repo), _) => open(Path::new(&repo)),
+        (None, _) if loc.exists() => open(loc),
+        (None, Some(repo)) => open(Path::new(repo)),
+        _ => {
             eprintln!("cloning rust repository");
-            Ok(RepoBuilder::new()
-                .bare(true)
-                .clone(RUST_SRC_URL, Path::new("rust.git"))?)
+            Ok(RepoBuilder::new().bare(true).clone(RUST_SRC_URL, loc)?)
         }
     }
 }