feat(revset): create main() function

git-branchless/src/revset/builtins.rs

@@ -39,6 +39,7 @@ lazy_static! {
             ("roots", &fn_roots),
             ("heads", &fn_heads),
             ("branches", &fn_branches),
+            ("main", &fn_main),
             ("public", &fn_public),
             ("draft", &fn_draft),
             ("stack", &fn_stack),
@@ -173,6 +174,11 @@ fn fn_nthancestor(ctx: &mut Context, name: &str, args: &[Expr]) -> EvalResult {
     Ok(CommitSet::from_iter(result.into_iter()))
 }
 
+fn fn_main(ctx: &mut Context, name: &str, args: &[Expr]) -> EvalResult {
+    eval0(ctx, name, args)?;
+    Ok(ctx.dag.main_branch_commit.clone())
+}
+
 fn fn_public(ctx: &mut Context, name: &str, args: &[Expr]) -> EvalResult {
     eval0(ctx, name, args)?;
     let public_commits = ctx.query_public_commits()?;

git-branchless/src/revset/eval.rs

@@ -560,6 +560,22 @@ mod tests {
             "###);
         }
 
+        {
+            let expr = Expr::FunctionCall(Cow::Borrowed("main"), vec![]);
+            insta::assert_debug_snapshot!(eval_and_sort(&effects, &repo, &mut dag, &expr), @r###"
+            Ok(
+                [
+                    Commit {
+                        inner: Commit {
+                            id: bf0d52a607f693201512a43b6b5a70b2a275e0ad,
+                            summary: "create test4.txt",
+                        },
+                    },
+                ],
+            )
+            "###);
+        }
+
         {
             let expr = Expr::FunctionCall(Cow::Borrowed("public"), vec![]);
             insta::assert_debug_snapshot!(eval_and_sort(&effects, &repo, &mut dag, &expr), @r###"

git-branchless/tests/command/test_query.rs

@@ -83,7 +83,7 @@ fn test_query_eval_error() -> eyre::Result<()> {
                 ..Default::default()
             },
         )?;
-        insta::assert_snapshot!(stderr, @"Evaluation error for expression 'foo()': no function with the name 'foo' could be found; these functions are available: all, ancestors, ancestors.nth, author.date, author.email, author.name, branches, children, committer.date, committer.email, committer.name, descendants, difference, draft, exactly, heads, intersection, message, none, not, only, parents, parents.nth, paths.changed, public, range, roots, stack, union
+        insta::assert_snapshot!(stderr, @"Evaluation error for expression 'foo()': no function with the name 'foo' could be found; these functions are available: all, ancestors, ancestors.nth, author.date, author.email, author.name, branches, children, committer.date, committer.email, committer.name, descendants, difference, draft, exactly, heads, intersection, main, message, none, not, only, parents, parents.nth, paths.changed, public, range, roots, stack, union
 ");
         insta::assert_snapshot!(stdout, @"");
     }