revset: split out no-args head() to visible_heads()

The `heads()` revset function with one argument is the counterpart to
`roots()`. Without arguments, it returns the visible heads in the
repo, i.e. `heads(all())`. The two use cases are quite different, and
I think it would be good to clarify that the no-arg form returns the
visible heads, so let's split that out to a new `visible_heads()`
function.

CHANGELOG.md

@@ -23,6 +23,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * The minimum supported Rust version (MSRV) is now 1.64.0.
 
+* The `heads()` revset function was split up into two functions. `heads()`
+  without arguments is now called `visible_heads()`. `heads()` with one argument
+  is unchanged.
+
 ### New features
 
 * `jj git push --deleted` will remove all locally deleted branches from the remote.

docs/revsets.md

@@ -104,9 +104,8 @@ revsets (expressions) as arguments.
 * `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.
-* `heads([x])`: Commits in `x` that are not ancestors of other commits in `x`.
-  If `x` was not specified, it selects all visible heads (as if you had said
-  `heads(all())`).
+* `visible_heads()`: All visible heads (same as `heads(all())`).
+* `heads(x)`: Commits in `x` that are not ancestors of other commits in `x`.
 * `roots(x)`: Commits in `x` that are not descendants of other commits in `x`.
 * `latest(x[, count])`: Latest `count` commits in `x`, based on committer
   timestamp. The default `count` is 1.

lib/src/default_revset_engine.rs

@@ -627,7 +627,7 @@ impl<'index, 'heads> EvaluationContext<'index, 'heads> {
                 // but if it does, the heads set could be extended to include the commits
                 // (and `remote_branches()`) specified in the revset expression. Alternatively,
                 // some optimization rules could be removed, but that means `author(_) & x`
-                // would have to test `:heads() & x`.
+                // would have to test `:visble_heads() & x`.
                 let walk = self.composite_index.walk_revs(self.visible_heads, &[]);
                 Ok(Box::new(RevWalkRevset { walk }))
             }

lib/src/revset.rs

@@ -798,19 +798,19 @@ static BUILTIN_FUNCTION_MAP: Lazy<HashMap<&'static str, RevsetFunction>> = Lazy:
         Ok(RevsetExpression::all())
     });
     map.insert("heads", |name, arguments_pair, state| {
-        let ([], [opt_arg]) = expect_arguments(name, arguments_pair)?;
-        if let Some(arg) = opt_arg {
-            let candidates = parse_expression_rule(arg.into_inner(), state)?;
-            Ok(candidates.heads())
-        } else {
-            Ok(RevsetExpression::visible_heads())
-        }
+        let arg = expect_one_argument(name, arguments_pair)?;
+        let candidates = parse_expression_rule(arg.into_inner(), state)?;
+        Ok(candidates.heads())
     });
     map.insert("roots", |name, arguments_pair, state| {
         let arg = expect_one_argument(name, arguments_pair)?;
         let candidates = parse_expression_rule(arg.into_inner(), state)?;
         Ok(candidates.roots())
     });
+    map.insert("visible_heads", |name, arguments_pair, _state| {
+        expect_no_arguments(name, arguments_pair)?;
+        Ok(RevsetExpression::visible_heads())
+    });
     map.insert("branches", |name, arguments_pair, state| {
         let ([], [opt_arg]) = expect_arguments(name, arguments_pair)?;
         let needle = if let Some(arg) = opt_arg {
@@ -2046,7 +2046,7 @@ mod tests {
         assert_eq!(parse("foo | -"), Err(RevsetParseErrorKind::SyntaxError));
         // Space is allowed around infix operators and function arguments
         assert_eq!(
-            parse("   description(  arg1 ) ~    file(  arg1 ,   arg2 )  ~ heads(  )  "),
+            parse("   description(  arg1 ) ~    file(  arg1 ,   arg2 )  ~ visible_heads(  )  "),
             Ok(
                 RevsetExpression::filter(RevsetFilterPredicate::Description("arg1".to_string()))
                     .minus(&RevsetExpression::filter(RevsetFilterPredicate::File(
@@ -2205,7 +2205,7 @@ mod tests {
             ))
         );
         assert_eq!(
-            parse("description(heads())"),
+            parse("description(visible_heads())"),
             Err(RevsetParseErrorKind::InvalidFunctionArguments {
                 name: "description".to_string(),
                 message: "Expected function argument of type string".to_string()

lib/tests/test_revset.rs

@@ -600,10 +600,10 @@ fn test_evaluate_expression_heads(use_git: bool) {
         vec![commit3.id().clone()]
     );
 
-    // Heads of all commits is the set of heads in the repo
+    // Heads of all commits is the set of visible heads in the repo
     assert_eq!(
         resolve_commit_ids(mut_repo, "heads(all())"),
-        resolve_commit_ids(mut_repo, "heads()")
+        resolve_commit_ids(mut_repo, "visible_heads()")
     );
 }
 
@@ -1187,7 +1187,7 @@ fn test_evaluate_expression_visible_heads(use_git: bool) {
     let commit3 = graph_builder.commit_with_parents(&[&commit1]);
 
     assert_eq!(
-        resolve_commit_ids(mut_repo, "heads()"),
+        resolve_commit_ids(mut_repo, "visible_heads()"),
         vec![commit3.id().clone(), commit2.id().clone()]
     );
 }
@@ -1626,7 +1626,7 @@ fn test_evaluate_expression_description(use_git: bool) {
     );
     // Searches only among candidates if specified
     assert_eq!(
-        resolve_commit_ids(mut_repo, "heads() & description(\"commit 2\")"),
+        resolve_commit_ids(mut_repo, "visible_heads() & description(\"commit 2\")"),
         vec![]
     );
 }
@@ -1692,7 +1692,7 @@ fn test_evaluate_expression_author(use_git: bool) {
     );
     // Searches only among candidates if specified
     assert_eq!(
-        resolve_commit_ids(mut_repo, "heads() & author(\"name2\")"),
+        resolve_commit_ids(mut_repo, "visible_heads() & author(\"name2\")"),
         vec![]
     );
     // Filter by union of pure predicate and set
@@ -1766,7 +1766,7 @@ fn test_evaluate_expression_committer(use_git: bool) {
     );
     // Searches only among candidates if specified
     assert_eq!(
-        resolve_commit_ids(mut_repo, "heads() & committer(\"name2\")"),
+        resolve_commit_ids(mut_repo, "visible_heads() & committer(\"name2\")"),
         vec![]
     );
 }

tests/test_revset_output.rs

@@ -98,7 +98,7 @@ fn test_bad_function_call() {
     1 | heads(foo, bar)
       |       ^------^
       |
-      = Invalid arguments to revset function "heads": Expected 0 to 1 arguments
+      = Invalid arguments to revset function "heads": Expected 1 arguments
     "###);
 
     let stderr = test_env.jj_cmd_failure(&repo_path, &["log", "-r", "latest(a, not_an_integer)"]);