commits: add a trait to describe storage backend and use-cases

Summary: This will be used to describe what the commit graph backend is.

Reviewed By: sfilipco

Differential Revision: D22970577

fbshipit-source-id: 753efdbdd4466730ece758d9f4789fbd21e2801b

eden/scm/lib/hgcommits/src/doublewrite.rs

@@ -6,6 +6,7 @@
  */
 
 use crate::AppendCommits;
+use crate::DescribeBackend;
 use crate::HgCommit;
 use crate::HgCommits;
 use crate::ReadCommitText;
@@ -165,3 +166,31 @@ impl ToSet for DoubleWriteCommits {
         self.commits.to_set(set)
     }
 }
+
+impl DescribeBackend for DoubleWriteCommits {
+    fn algorithm_backend(&self) -> &'static str {
+        "segments"
+    }
+
+    fn describe_backend(&self) -> String {
+        format!(
+            r#"Backend (doublewrite):
+  Local:
+    Segments + IdMap: {}
+    Zstore: {}
+    Revlog + Nodemap: {}
+Feature Providers:
+  Commit Graph Algorithms:
+    Segments
+  Commit Hash / Rev Lookup:
+    IdMap
+  Commit Data (user, message):
+    Zstore (incomplete)
+    Revlog
+"#,
+            self.commits.dag_path.display(),
+            self.commits.commits_path.display(),
+            self.revlog.dir.join("00changelog.{i,d,nodemap}").display(),
+        )
+    }
+}

eden/scm/lib/hgcommits/src/hgsha1commits.rs

@@ -7,6 +7,7 @@
 
 use crate::strip;
 use crate::AppendCommits;
+use crate::DescribeBackend;
 use crate::HgCommit;
 use crate::ReadCommitText;
 use crate::StripCommits;
@@ -37,9 +38,9 @@ use zstore::Zstore;
 /// Commits using the HG SHA1 hash function. Stored on disk.
 pub struct HgCommits {
     commits: Zstore,
-    commits_path: PathBuf,
+    pub(crate) commits_path: PathBuf,
     dag: Dag,
-    dag_path: PathBuf,
+    pub(crate) dag_path: PathBuf,
 }
 
 impl HgCommits {
@@ -238,3 +239,28 @@ impl ToSet for HgCommits {
         self.dag.to_set(set)
     }
 }
+
+impl DescribeBackend for HgCommits {
+    fn algorithm_backend(&self) -> &'static str {
+        "segments"
+    }
+
+    fn describe_backend(&self) -> String {
+        format!(
+            r#"Backend (non-lazy segments):
+  Local:
+    Segments + IdMap: {}
+    Zstore: {}
+Feature Providers:
+  Commit Graph Algorithms:
+    Segments
+  Commit Hash / Rev Lookup:
+    IdMap
+  Commit Data (user, message):
+    Zstore
+"#,
+            self.dag_path.display(),
+            self.commits_path.display()
+        )
+    }
+}

eden/scm/lib/hgcommits/src/lib.rs

@@ -28,6 +28,14 @@ pub trait AppendCommits {
     fn flush(&mut self, master_heads: &[Vertex]) -> Result<()>;
 }
 
+pub trait DescribeBackend {
+    /// Name of the DagAlgorithm backend.
+    fn algorithm_backend(&self) -> &'static str;
+
+    /// Describe what storage backend is being used.
+    fn describe_backend(&self) -> String;
+}
+
 /// Parameter used by `add_commits`.
 #[derive(Clone, Debug, Serialize, Deserialize)]
 pub struct HgCommit {

eden/scm/lib/hgcommits/src/memhgcommits.rs

@@ -7,6 +7,7 @@
 
 use crate::strip;
 use crate::AppendCommits;
+use crate::DescribeBackend;
 use crate::HgCommit;
 use crate::ReadCommitText;
 use crate::StripCommits;
@@ -189,3 +190,24 @@ impl ToSet for MemHgCommits {
         self.dag.to_set(set)
     }
 }
+
+impl DescribeBackend for MemHgCommits {
+    fn algorithm_backend(&self) -> &'static str {
+        "segments"
+    }
+
+    fn describe_backend(&self) -> String {
+        r#"Backend (memory):
+  Local:
+    Memory
+Feature Providers:
+  Commit Graph Algorithms:
+    Memory
+  Commit Hash / Rev Lookup:
+    Memory
+  Commit Data (user, message):
+    Memory
+"#
+        .to_string()
+    }
+}

eden/scm/lib/hgcommits/src/revlog.rs

@@ -7,6 +7,7 @@
 
 use crate::strip;
 use crate::AppendCommits;
+use crate::DescribeBackend;
 use crate::HgCommit;
 use crate::ReadCommitText;
 use crate::StripCommits;
@@ -30,7 +31,7 @@ use std::path::PathBuf;
 /// HG commits stored on disk using the revlog format.
 pub struct RevlogCommits {
     revlog: RevlogIndex,
-    dir: PathBuf,
+    pub(crate) dir: PathBuf,
 }
 
 impl RevlogCommits {
@@ -179,3 +180,28 @@ impl ToSet for RevlogCommits {
         self.revlog.to_set(set)
     }
 }
+
+impl DescribeBackend for RevlogCommits {
+    fn algorithm_backend(&self) -> &'static str {
+        "revlog"
+    }
+
+    fn describe_backend(&self) -> String {
+        format!(
+            r#"Backend (revlog):
+  Local:
+    Revlog: {}
+    Nodemap: {}
+Feature Providers:
+  Commit Graph Algorithms:
+    Revlog
+  Commit Hash / Rev Lookup:
+    Nodemap
+  Commit Data (user, message):
+    Revlog
+"#,
+            self.dir.join("00changelog.{i,d}").display(),
+            self.dir.join("00changelog.nodemap").display(),
+        )
+    }
+}