revset: make present(unknown@) recover from missing working copy error

Missing working-copy commit is similar situation to unknown ref, and should
be caught by present().

CHANGELOG.md

@@ -107,6 +107,10 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 * Editing a hidden commit now makes it visible.
 
+* The `present()` revset now suppresses missing working copy error. For example,
+  `present(@)` evaluates to `none()` if the current workspace has no
+  working-copy commit.
+
 ## [0.21.0] - 2024-09-04
 
 ### Breaking changes

lib/src/revset.rs

@@ -1866,11 +1866,11 @@ fn resolve_symbols(
             RevsetExpression::Present(candidates) => {
                 resolve_symbols(repo, candidates.clone(), symbol_resolver)
                     .or_else(|err| match err {
-                        RevsetResolutionError::NoSuchRevision { .. } => {
+                        RevsetResolutionError::NoSuchRevision { .. }
+                        | RevsetResolutionError::WorkspaceMissingWorkingCopy { .. } => {
                             Ok(RevsetExpression::none())
                         }
-                        RevsetResolutionError::WorkspaceMissingWorkingCopy { .. }
-                        | RevsetResolutionError::EmptyString
+                        RevsetResolutionError::EmptyString
                         | RevsetResolutionError::AmbiguousCommitIdPrefix(_)
                         | RevsetResolutionError::AmbiguousChangeIdPrefix(_)
                         | RevsetResolutionError::StoreError(_)

lib/tests/test_revset.rs

@@ -14,6 +14,7 @@
 
 use std::iter;
 use std::path::Path;
+use std::rc::Rc;
 
 use assert_matches::assert_matches;
 use chrono::DateTime;
@@ -390,6 +391,18 @@ fn test_resolve_working_copy() {
         Err(RevsetResolutionError::WorkspaceMissingWorkingCopy { name }) if name == "ws1"
     );
 
+    // The error can be suppressed by present()
+    assert_eq!(
+        Rc::new(RevsetExpression::Present(RevsetExpression::working_copy(
+            ws1.clone()
+        )))
+        .evaluate_programmatic(mut_repo)
+        .unwrap()
+        .iter()
+        .collect_vec(),
+        vec![]
+    );
+
     // Add some workspaces
     mut_repo
         .set_wc_commit(ws1.clone(), commit1.id().clone())