templater: Add operation.snapshot() boolean

Expose the information we now record, to allow changing the default "snapshot
working copy" message or to make snapshots more compact/less distracting in
the log

CHANGELOG.md

@@ -30,6 +30,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * File path arguments now support [file pattern
   syntax](docs/filesets.md#file-patterns).
 
+* Operation objects in templates now have a `snapshot() -> Boolean` method that
+  evaluates to true if the operation was a snapshot created by a non-mutating
+  command (e.g. `jj log`).
+
 ### Fixed bugs
 
 * Revsets now support `\`-escapes in string literal.
@@ -231,7 +235,7 @@ No code changes (fixing Rust `Cargo.toml` stuff).
   When symlink support is unavailable, they will be materialized as regular files in the
   working copy (instead of resulting in a crash).
   [#2](https://github.com/martinvonz/jj/issues/2)
-  
+
 * On Windows, the `:builtin` pager is now used by default, rather than being
   disabled entirely.
 
@@ -278,7 +282,7 @@ Thanks to the people who made this release happen!
   copy commit on top of a single specified revision, i.e. with one parent.
   `merge` creates a new working copy commit on top of *at least* two specified
   revisions, i.e. with two or more parents.
-  
+
   The only difference between these commands and `jj new`, which *also* creates
   a new working copy commit, is that `new` can create a working copy commit on
   top of any arbitrary number of revisions, so it can handle both the previous
@@ -435,7 +439,7 @@ Thanks to the people who made this release happen!
 
 * `jj branch set` no longer creates a new branch. Use `jj branch create`
   instead.
-  
+
 * `jj init --git` in an existing Git repository now errors and exits rather than
   creating a second Git store.
 
@@ -599,8 +603,8 @@ Thanks to the people who made this release happen!
 
 ### New features
 
-* The `ancestors()` revset function now takes an optional `depth` argument 
-  to limit the depth of the ancestor set. For example, use `jj log -r 
+* The `ancestors()` revset function now takes an optional `depth` argument
+  to limit the depth of the ancestor set. For example, use `jj log -r
   'ancestors(@, 5)` to view the last 5 commits.
 
 * Support for the Watchman filesystem monitor is now bundled by default. Set
@@ -765,13 +769,13 @@ Thanks to the people who made this release happen!
   respectively.
 
 * `jj log` timestamp format now accepts `.utc()` to convert a timestamp to UTC.
- 
+
 * templates now support additional string methods `.starts_with(x)`, `.ends_with(x)`
   `.remove_prefix(x)`, `.remove_suffix(x)`, and `.substr(start, end)`.
 
 * `jj next` and `jj prev` are added, these allow you to traverse the history
   in a linear style. For people coming from Sapling and `git-branchles`
-  see [#2126](https://github.com/martinvonz/jj/issues/2126) for 
+  see [#2126](https://github.com/martinvonz/jj/issues/2126) for
   further pending improvements.
 
 * `jj diff --stat` has been implemented. It shows a histogram of the changes,

cli/src/operation_templater.rs

@@ -249,6 +249,14 @@ fn builtin_operation_methods() -> OperationTemplateBuildMethodFnMap<Operation> {
         });
         Ok(L::wrap_string(out_property))
     });
+    map.insert(
+        "snapshot",
+        |_language, _build_ctx, self_property, function| {
+            template_parser::expect_no_arguments(function)?;
+            let out_property = self_property.map(|op| op.metadata().is_snapshot);
+            Ok(L::wrap_boolean(out_property))
+        },
+    );
     map.insert("time", |_language, _build_ctx, self_property, function| {
         template_parser::expect_no_arguments(function)?;
         let out_property = self_property.map(|op| TimestampRange {

docs/templates.md

@@ -133,7 +133,8 @@ This type cannot be printed. The following methods are defined.
 * `tags() -> String`
 * `time() -> TimestampRange`
 * `user() -> String`
-* `root() -> Boolean`: True if the commit is the root commit.
+* `snapshot() -> Boolean`: True if the operation is a snapshot operation.
+* `root() -> Boolean`: True if the operation is the root operation.
 
 ### OperationId type