revset: resolve "HEAD@git" just like other pseudo @git branches

I don't think this would be practically useful, but consistent UX is
important.

Fixes #1843

docs/revsets.md

@@ -102,7 +102,8 @@ revsets (expressions) as arguments.
   possible targets are included.
 * `git_refs()`:  All Git ref targets as of the last import. If a Git ref
   is in a conflicted state, all its possible targets are included.
-* `git_head()`: The Git `HEAD` target as of the last import.
+* `git_head()`: The Git `HEAD` target as of the last import. Equivalent to
+  `present(HEAD@git)`.
 * `visible_heads()`: All visible heads (same as `heads(all())`).
 * `heads(x)`: Commits in `x` that are not ancestors of other commits in `x`.
   Note that this is different from

lib/src/revset.rs

@@ -1653,7 +1653,11 @@ fn resolve_branch(repo: &dyn Repo, symbol: &str) -> Option<Vec<CommitId>> {
         }
         // A remote with name "git" will shadow local-git tracking branches
         if remote_name == "git" {
-            if let Some(target) = get_local_git_tracking_branch(view, name) {
+            let maybe_target = match name {
+                "HEAD" => view.git_head(),
+                _ => get_local_git_tracking_branch(view, name),
+            };
+            if let Some(target) = maybe_target {
                 return Some(target.adds().to_vec());
             }
         }
@@ -1662,7 +1666,8 @@ fn resolve_branch(repo: &dyn Repo, symbol: &str) -> Option<Vec<CommitId>> {
 }
 
 fn collect_branch_symbols(repo: &dyn Repo, include_synced_remotes: bool) -> Vec<String> {
-    let (all_branches, _) = git::build_unified_branches_map(repo.view());
+    let view = repo.view();
+    let (all_branches, _) = git::build_unified_branches_map(view);
     all_branches
         .iter()
         .flat_map(|(name, branch_target)| {
@@ -1675,6 +1680,7 @@ fn collect_branch_symbols(repo: &dyn Repo, include_synced_remotes: bool) -> Vec<
                 .map(move |(remote_name, _)| format!("{name}@{remote_name}"));
             local_symbol.into_iter().chain(remote_symbols)
         })
+        .chain(view.git_head().is_some().then(|| "HEAD@git".to_owned()))
         .collect()
 }
 

lib/tests/test_revset.rs

@@ -621,6 +621,50 @@ fn test_resolve_symbol_branches() {
     "###);
 }
 
+#[test]
+fn test_resolve_symbol_git_head() {
+    let settings = testutils::user_settings();
+    let test_repo = TestRepo::init(true);
+    let repo = &test_repo.repo;
+
+    let mut tx = repo.start_transaction(&settings, "test");
+    let mut_repo = tx.mut_repo();
+
+    let commit1 = write_random_commit(mut_repo, &settings);
+
+    // Without HEAD@git
+    insta::assert_debug_snapshot!(
+        resolve_symbol(mut_repo, "HEAD", None).unwrap_err(), @r###"
+    NoSuchRevision {
+        name: "HEAD",
+        candidates: [],
+    }
+    "###);
+    insta::assert_debug_snapshot!(
+        resolve_symbol(mut_repo, "HEAD@git", None).unwrap_err(), @r###"
+    NoSuchRevision {
+        name: "HEAD@git",
+        candidates: [],
+    }
+    "###);
+
+    // With HEAD@git
+    mut_repo.set_git_head(RefTarget::Normal(commit1.id().clone()));
+    insta::assert_debug_snapshot!(
+        resolve_symbol(mut_repo, "HEAD", None).unwrap_err(), @r###"
+    NoSuchRevision {
+        name: "HEAD",
+        candidates: [
+            "HEAD@git",
+        ],
+    }
+    "###);
+    assert_eq!(
+        resolve_symbol(mut_repo, "HEAD@git", None).unwrap(),
+        vec![commit1.id().clone()],
+    );
+}
+
 #[test]
 fn test_resolve_symbol_git_refs() {
     let settings = testutils::user_settings();