feat: one store directory per checkout

tests/support/mod.rs

@@ -7,6 +7,7 @@
 #![allow(dead_code)]
 use std::ffi::OsStr;
 use std::fmt::Write as _;
+use std::os::unix::ffi::OsStrExt;
 use std::path::{Path, PathBuf};
 use std::process::{Command, Output};
 use std::sync::atomic::{AtomicU32, Ordering};
@@ -15,8 +16,12 @@ use std::{env, fs};
 // unique per case even with the suite running in parallel
 static NEXT: AtomicU32 = AtomicU32::new(0);
 
+pub const REMOTE: &str = "https://git.example.org/acme/proj.git";
+
 pub struct Case {
     root: PathBuf,
+    // the data home every checkout of a case shares, as one user's would
+    xdg: PathBuf,
     pub repo: PathBuf,
     pub store: PathBuf,
     pub outside: PathBuf,
@@ -32,29 +37,41 @@ impl Case {
         ));
         let _ = fs::remove_dir_all(&root);
 
-        let case = Self {
-            repo: root.join("repo"),
-            store: root
-                .join("xdg/ahab/git.example.org/acme/proj")
-                .to_path_buf(),
-            outside: root.join("outside"),
-            root,
-        };
+        Self::checkout(root.clone(), root.join("xdg"))
+    }
 
-        for dir in [&case.repo, &case.outside] {
+    // a second clone of the same remote, sharing the first one's data home
+    pub fn second_checkout(&self) -> Self {
+        Self::checkout(self.root.join("second"), self.xdg.clone())
+    }
+
+    fn checkout(root: PathBuf, xdg: PathBuf) -> Self {
+        let repo = root.join("repo");
+        let outside = root.join("outside");
+        for dir in [&repo, &outside] {
             fs::create_dir_all(dir).expect("creating the case directories");
         }
 
+        // `<dir>-<hash>` of the canonical checkout, as ahab spells it
+        let canonical = fs::canonicalize(&repo).expect("resolving the repository");
+        let store = xdg.join("ahab/git.example.org/acme/proj").join(format!(
+            "repo-{}",
+            fingerprint(canonical.as_os_str().as_bytes())
+        ));
+
+        let case = Self {
+            root,
+            xdg,
+            repo,
+            store,
+            outside,
+        };
+
         case.git(&["init", "-q", "."]);
         case.git(&["config", "user.email", "test@example.org"]);
         case.git(&["config", "user.name", "test"]);
         case.git(&["config", "commit.gpgsign", "false"]);
-        case.git(&[
-            "remote",
-            "add",
-            "origin",
-            "https://git.example.org/acme/proj.git",
-        ]);
+        case.git(&["remote", "add", "origin", REMOTE]);
         case.write("tracked.txt", b"tracked\n");
         case.git(&["add", "tracked.txt"]);
         case.git(&["commit", "-qm", "init"]);
@@ -84,7 +101,7 @@ impl Case {
     pub fn ahab<S: AsRef<OsStr>>(&self, args: &[S]) -> Run {
         let out = Command::new(env!("CARGO_BIN_EXE_ahab"))
             .current_dir(&self.repo)
-            .env("XDG_DATA_HOME", self.root.join("xdg"))
+            .env("XDG_DATA_HOME", &self.xdg)
             // the git commands ahab runs must not read the developer's own config
             .env("GIT_CONFIG_GLOBAL", "/dev/null")
             .env("GIT_CONFIG_SYSTEM", "/dev/null")
@@ -205,3 +222,15 @@ impl Run {
         out
     }
 }
+
+// fnv-1a, as the store spells a checkout
+pub fn fingerprint(bytes: &[u8]) -> String {
+    let mut hash: u64 = 0xcbf2_9ce4_8422_2325;
+
+    for byte in bytes {
+        hash ^= u64::from(*byte);
+        hash = hash.wrapping_mul(0x100_0000_01b3);
+    }
+
+    format!("{:08x}", hash as u32)
+}