cli: teach log flag to show commits in reverse order

This adds a `--reversed` flag to `jj log` to show commits with later
commits further down. It works both with and without the graph.

Since the graph-drawing code is already independent of the
relationship between commits, it doesn't need any updating.

CHANGELOG.md

@@ -88,6 +88,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * Aliases can now call other aliases.
 
+* `jj log` now accepts a `--reversed` option, which will show older commits
+  first.
+
 ### Fixed bugs
 
 * When rebasing a conflict where one side modified a file and the other side

lib/src/revset.rs

@@ -833,6 +833,12 @@ impl<'revset, 'repo> RevsetIterator<'revset, 'repo> {
         }
     }
 
+    pub fn reversed(self) -> ReverseRevsetIterator<'repo> {
+        ReverseRevsetIterator {
+            entries: self.into_iter().collect_vec(),
+        }
+    }
+
     pub fn graph(self) -> RevsetGraphIterator<'revset, 'repo> {
         RevsetGraphIterator::new(self)
     }
@@ -873,6 +879,18 @@ impl Iterator for RevsetCommitIterator<'_, '_> {
     }
 }
 
+pub struct ReverseRevsetIterator<'repo> {
+    entries: Vec<IndexEntry<'repo>>,
+}
+
+impl<'repo> Iterator for ReverseRevsetIterator<'repo> {
+    type Item = IndexEntry<'repo>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.entries.pop()
+    }
+}
+
 struct EagerRevset<'repo> {
     index_entries: Vec<IndexEntry<'repo>>,
 }

src/commands.rs

@@ -42,7 +42,7 @@ use jujutsu_lib::diff::{Diff, DiffHunk};
 use jujutsu_lib::files::DiffLine;
 use jujutsu_lib::git::{GitExportError, GitFetchError, GitImportError, GitRefUpdate};
 use jujutsu_lib::gitignore::GitIgnoreFile;
-use jujutsu_lib::index::HexPrefix;
+use jujutsu_lib::index::{HexPrefix, IndexEntry};
 use jujutsu_lib::matchers::{EverythingMatcher, Matcher, PrefixMatcher, Visit};
 use jujutsu_lib::op_heads_store::{OpHeadResolutionError, OpHeads, OpHeadsStore};
 use jujutsu_lib::op_store::{OpStore, OpStoreError, OperationId, RefTarget, WorkspaceId};
@@ -51,7 +51,7 @@ use jujutsu_lib::refs::{classify_branch_push_action, BranchPushAction, BranchPus
 use jujutsu_lib::repo::{MutableRepo, ReadonlyRepo, RepoRef};
 use jujutsu_lib::repo_path::RepoPath;
 use jujutsu_lib::revset::{RevsetError, RevsetExpression, RevsetParseError};
-use jujutsu_lib::revset_graph_iterator::RevsetGraphEdgeType;
+use jujutsu_lib::revset_graph_iterator::{RevsetGraphEdge, RevsetGraphEdgeType};
 use jujutsu_lib::rewrite::{back_out_commit, merge_commit_trees, rebase_commit, DescendantRebaser};
 use jujutsu_lib::settings::UserSettings;
 use jujutsu_lib::store::Store;
@@ -1280,6 +1280,9 @@ struct LogArgs {
         default_value = "remote_branches().. | (remote_branches()..)-"
     )]
     revisions: String,
+    /// Show revisions in the opposite order (older revisions first)
+    #[clap(long)]
+    reversed: bool,
     /// Don't show the graph, show a flat list of revisions
     #[clap(long)]
     no_graph: bool,
@@ -3016,7 +3019,12 @@ fn cmd_log(ui: &mut Ui, command: &CommandHelper, args: &LogArgs) -> Result<(), C
 
     if !args.no_graph {
         let mut graph = AsciiGraphDrawer::new(&mut formatter);
-        for (index_entry, edges) in revset.iter().graph() {
+        let iter: Box<dyn Iterator<Item = (IndexEntry, Vec<RevsetGraphEdge>)>> = if args.reversed {
+            Box::new(revset.iter().graph().reversed())
+        } else {
+            Box::new(revset.iter().graph())
+        };
+        for (index_entry, edges) in iter {
             let mut graphlog_edges = vec![];
             // TODO: Should we update RevsetGraphIterator to yield this flag instead of all
             // the missing edges since we don't care about where they point here
@@ -3072,7 +3080,12 @@ fn cmd_log(ui: &mut Ui, command: &CommandHelper, args: &LogArgs) -> Result<(), C
             )?;
         }
     } else {
-        for index_entry in revset.iter() {
+        let iter: Box<dyn Iterator<Item = IndexEntry>> = if args.reversed {
+            Box::new(revset.iter().reversed())
+        } else {
+            Box::new(revset.iter())
+        };
+        for index_entry in iter {
             let commit = store.get_commit(&index_entry.commit_id())?;
             template.format(&commit, formatter)?;
             if let Some(diff_format) = diff_format {

tests/test_log_command.rs

@@ -128,3 +128,30 @@ fn test_log_with_or_without_diff() {
     +bar
     "###);
 }
+
+#[test]
+fn test_log_reversed() {
+    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, &["describe", "-m", "first"]);
+    test_env.jj_cmd_success(&repo_path, &["new", "-m", "second"]);
+
+    let stdout = test_env.jj_cmd_success(&repo_path, &["log", "-T", "description", "--reversed"]);
+    insta::assert_snapshot!(stdout, @r###"
+    o 
+    o first
+    @ second
+    "###);
+
+    let stdout = test_env.jj_cmd_success(
+        &repo_path,
+        &["log", "-T", "description", "--reversed", "--no-graph"],
+    );
+    insta::assert_snapshot!(stdout, @r###"
+    
+    first
+    second
+    "###);
+}