feat(cli): Use a local git rev as a baseline

Fixes #51

Cargo.toml

@@ -31,3 +31,4 @@ clap-cargo = { version = "0.9.1", features = ["cargo_metadata"] }
 ignore = "0.4.18"
 clap-verbosity-flag = "1.0.1"
 log = "0.4.17"
+git2 = { version = "0.15.0", default-features = false }

src/baseline.rs

@@ -72,3 +72,44 @@ impl BaselineLoader for PathBaseline {
         Ok(rustdoc_path)
     }
 }
+
+pub(crate) struct GitBaseline {
+    path: PathBaseline,
+}
+
+impl GitBaseline {
+    pub fn with_rev(
+        source: &std::path::Path,
+        target: &std::path::Path,
+        rev: &str,
+        config: &mut GlobalConfig,
+    ) -> anyhow::Result<Self> {
+        config.shell_status("Cloning", rev)?;
+        let repo = git2::Repository::discover(source)?;
+
+        let rev = repo.revparse_single(rev)?;
+
+        std::fs::create_dir_all(target)?;
+        let mut co = git2::build::CheckoutBuilder::new();
+        co.target_dir(target)
+            .remove_untracked(true)
+            .remove_ignored(true)
+            .use_ours(true)
+            .force();
+        repo.checkout_tree(&rev, Some(&mut co))?;
+
+        let path = PathBaseline::new(target)?;
+        Ok(Self { path })
+    }
+}
+
+impl BaselineLoader for GitBaseline {
+    fn load_rustdoc(
+        &self,
+        config: &mut GlobalConfig,
+        rustdoc: &RustDocCommand,
+        name: &str,
+    ) -> anyhow::Result<std::path::PathBuf> {
+        self.path.load_rustdoc(config, rustdoc, name)
+    }
+}

src/main.rs

@@ -30,6 +30,23 @@ fn main() -> anyhow::Result<()> {
                     Box::new(baseline::RustdocBaseline::new(path.to_owned()))
                 } else if let Some(root) = args.baseline_root.as_deref() {
                     Box::new(baseline::PathBaseline::new(root)?)
+                } else if let Some(rev) = args.baseline_rev.as_deref() {
+                    let metadata = args.manifest.metadata().no_deps().exec()?;
+                    let source = metadata.workspace_root.as_std_path();
+                    let slug = rev
+                        .chars()
+                        .filter(|c| c.is_alphanumeric())
+                        .collect::<String>();
+                    let target = metadata
+                        .target_directory
+                        .as_std_path()
+                        .join(format!("semver-checks/git-{}", slug));
+                    Box::new(baseline::GitBaseline::with_rev(
+                        source,
+                        &target,
+                        rev,
+                        &mut config,
+                    )?)
                 } else {
                     unreachable!("a member of the `baseline` group must be present");
                 };
@@ -134,6 +151,15 @@ struct CheckRelease {
     )]
     baseline_root: Option<PathBuf>,
 
+    /// Git revision to lookup for a baseline
+    #[clap(
+        long,
+        value_name = "REV",
+        help_heading = "BASELINE",
+        group = "baseline"
+    )]
+    baseline_rev: Option<String>,
+
     /// The rustdoc json file to use as a semver baseline.
     #[clap(
         long,