templater: add "parent_commit_ids" keyword

A list type isn't so useful without a map operation, but List<CommitId>
is at least printable. Maybe we can experiment with it to craft a map
operation.

If a map operation is introduced, this keyword might be replaced with
"parents.map(|commit| commit.commit_id)", where parents is of List<Commit>
type, and the .map() method will probably return List<Template>.

docs/templates.md

@@ -18,6 +18,7 @@ The following keywords can be used in `jj log`/`jj obslog` templates.
 * `description: String`
 * `change_id: ChangeId`
 * `commit_id: CommitId`
+* `parent_commit_ids: List<CommitId>`
 * `author: Signature`
 * `committer: Signature`
 * `working_copies: String`: For multi-workspace repository, indicate
@@ -83,6 +84,10 @@ The following methods are defined.
 
 No methods are defined.
 
+### List type
+
+No methods are defined.
+
 ### OperationId type
 
 The following methods are defined.

src/commit_templater.rs

@@ -30,7 +30,7 @@ use crate::template_parser::{
     TemplateLanguage, TemplateParseError, TemplateParseResult,
 };
 use crate::templater::{
-    IntoTemplate, PlainTextFormattedProperty, Template, TemplateProperty, TemplatePropertyFn,
+    self, IntoTemplate, PlainTextFormattedProperty, Template, TemplateProperty, TemplatePropertyFn,
 };
 
 struct CommitTemplateLanguage<'repo, 'b> {
@@ -60,6 +60,9 @@ impl<'repo> TemplateLanguage<'repo> for CommitTemplateLanguage<'repo, '_> {
             CommitTemplatePropertyKind::CommitOrChangeId(property) => {
                 build_commit_or_change_id_method(self, property, function)
             }
+            CommitTemplatePropertyKind::CommitOrChangeIdList(property) => {
+                template_parser::build_list_method(self, property, function)
+            }
             CommitTemplatePropertyKind::ShortestIdPrefix(property) => {
                 build_shortest_id_prefix_method(self, property, function)
             }
@@ -77,6 +80,13 @@ impl<'repo> CommitTemplateLanguage<'repo, '_> {
         CommitTemplatePropertyKind::CommitOrChangeId(property)
     }
 
+    fn wrap_commit_or_change_id_list(
+        &self,
+        property: Box<dyn TemplateProperty<Commit, Output = Vec<CommitOrChangeId<'repo>>> + 'repo>,
+    ) -> CommitTemplatePropertyKind<'repo> {
+        CommitTemplatePropertyKind::CommitOrChangeIdList(property)
+    }
+
     fn wrap_shortest_id_prefix(
         &self,
         property: Box<dyn TemplateProperty<Commit, Output = ShortestIdPrefix> + 'repo>,
@@ -88,13 +98,17 @@ impl<'repo> CommitTemplateLanguage<'repo, '_> {
 enum CommitTemplatePropertyKind<'repo> {
     Core(CoreTemplatePropertyKind<'repo, Commit>),
     CommitOrChangeId(Box<dyn TemplateProperty<Commit, Output = CommitOrChangeId<'repo>> + 'repo>),
+    CommitOrChangeIdList(
+        Box<dyn TemplateProperty<Commit, Output = Vec<CommitOrChangeId<'repo>>> + 'repo>,
+    ),
     ShortestIdPrefix(Box<dyn TemplateProperty<Commit, Output = ShortestIdPrefix> + 'repo>),
 }
 
 impl<'repo> IntoTemplateProperty<'repo, Commit> for CommitTemplatePropertyKind<'repo> {
     fn try_into_boolean(self) -> Option<Box<dyn TemplateProperty<Commit, Output = bool> + 'repo>> {
         match self {
             CommitTemplatePropertyKind::Core(property) => property.try_into_boolean(),
+            // TODO: should we allow implicit cast of List type?
             _ => None,
         }
     }
@@ -119,6 +133,7 @@ impl<'repo> IntoTemplate<'repo, Commit> for CommitTemplatePropertyKind<'repo> {
         match self {
             CommitTemplatePropertyKind::Core(property) => property.into_template(),
             CommitTemplatePropertyKind::CommitOrChangeId(property) => property.into_template(),
+            CommitTemplatePropertyKind::CommitOrChangeIdList(property) => property.into_template(),
             CommitTemplatePropertyKind::ShortestIdPrefix(property) => property.into_template(),
         }
     }
@@ -152,6 +167,13 @@ fn build_commit_keyword<'repo>(
         "commit_id" => language.wrap_commit_or_change_id(wrap_fn(move |commit| {
             CommitOrChangeId::new(repo, IdKind::Commit(commit.id().to_owned()))
         })),
+        "parent_commit_ids" => language.wrap_commit_or_change_id_list(wrap_fn(move |commit| {
+            commit
+                .parent_ids()
+                .iter()
+                .map(|id| CommitOrChangeId::new(repo, IdKind::Commit(id.to_owned())))
+                .collect()
+        })),
         "author" => language.wrap_signature(wrap_fn(|commit| commit.author().clone())),
         "committer" => language.wrap_signature(wrap_fn(|commit| commit.committer().clone())),
         "working_copies" => language.wrap_string(wrap_repo_fn(repo, extract_working_copies)),
@@ -179,6 +201,7 @@ fn build_commit_keyword<'repo>(
     Ok(property)
 }
 
+// TODO: return Vec<String>
 fn extract_working_copies(repo: &dyn Repo, commit: &Commit) -> String {
     let wc_commit_ids = repo.view().wc_commit_ids();
     if wc_commit_ids.len() <= 1 {
@@ -193,6 +216,7 @@ fn extract_working_copies(repo: &dyn Repo, commit: &Commit) -> String {
     names.join(" ")
 }
 
+// TODO: return Vec<Branch>?
 fn extract_branches(repo: &dyn Repo, commit: &Commit) -> String {
     let mut names = vec![];
     for (branch_name, branch_target) in repo.view().branches() {
@@ -225,6 +249,7 @@ fn extract_branches(repo: &dyn Repo, commit: &Commit) -> String {
     names.join(" ")
 }
 
+// TODO: return Vec<NameRef>?
 fn extract_tags(repo: &dyn Repo, commit: &Commit) -> String {
     let mut names = vec![];
     for (tag_name, target) in repo.view().tags() {
@@ -239,6 +264,7 @@ fn extract_tags(repo: &dyn Repo, commit: &Commit) -> String {
     names.join(" ")
 }
 
+// TODO: return Vec<NameRef>?
 fn extract_git_refs(repo: &dyn Repo, commit: &Commit) -> String {
     // TODO: We should keep a map from commit to ref names so we don't have to walk
     // all refs here.
@@ -255,6 +281,7 @@ fn extract_git_refs(repo: &dyn Repo, commit: &Commit) -> String {
     names.join(" ")
 }
 
+// TODO: return NameRef?
 fn extract_git_head(repo: &dyn Repo, commit: &Commit) -> String {
     match repo.view().git_head() {
         Some(ref_target) if ref_target.has_add(commit.id()) => {
@@ -322,6 +349,12 @@ impl Template<()> for CommitOrChangeId<'_> {
     }
 }
 
+impl Template<()> for Vec<CommitOrChangeId<'_>> {
+    fn format(&self, _: &(), formatter: &mut dyn Formatter) -> io::Result<()> {
+        templater::format_joined(&(), formatter, self, " ")
+    }
+}
+
 fn build_commit_or_change_id_method<'repo>(
     language: &CommitTemplateLanguage<'repo, '_>,
     self_property: impl TemplateProperty<Commit, Output = CommitOrChangeId<'repo>> + 'repo,

src/template_parser.rs

@@ -1040,6 +1040,15 @@ fn build_timestamp_range_method<'a, L: TemplateLanguage<'a>>(
     Ok(property)
 }
 
+pub fn build_list_method<'a, L: TemplateLanguage<'a>, P>(
+    _language: &L,
+    _self_property: impl TemplateProperty<L::Context, Output = Vec<P>> + 'a,
+    function: &FunctionCallNode,
+) -> TemplateParseResult<L::Property> {
+    // TODO: .join(separator), .map(), ...
+    Err(TemplateParseError::no_such_method("List", function))
+}
+
 fn build_global_function<'a, L: TemplateLanguage<'a>>(
     language: &L,
     function: &FunctionCallNode,

tests/test_commit_template.rs

@@ -17,6 +17,30 @@ use regex::Regex;
 
 pub mod common;
 
+#[test]
+fn test_log_parent_commit_ids() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_success(test_env.env_root(), &["init", "repo", "--git"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    test_env.jj_cmd_success(&repo_path, &["new"]);
+    test_env.jj_cmd_success(&repo_path, &["new", "@-"]);
+    test_env.jj_cmd_success(&repo_path, &["new", "@", "@-"]);
+
+    let template = r#"commit_id ++ "\nP: " ++ parent_commit_ids ++ "\n""#;
+    let stdout = test_env.jj_cmd_success(&repo_path, &["log", "-T", template]);
+    insta::assert_snapshot!(stdout, @r###"
+    @    c067170d4ca1bc6162b64f7550617ec809647f84
+    ├─╮  P: 4db490c88528133d579540b6900b8098f0c17701 230dd059e1b059aefc0da06a2e5a7dbf22362f22
+    o │  4db490c88528133d579540b6900b8098f0c17701
+    ├─╯  P: 230dd059e1b059aefc0da06a2e5a7dbf22362f22
+    o  230dd059e1b059aefc0da06a2e5a7dbf22362f22
+    │  P: 0000000000000000000000000000000000000000
+    o  0000000000000000000000000000000000000000
+       P:
+    "###);
+}
+
 #[test]
 fn test_log_author_timestamp() {
     let test_env = TestEnvironment::default();