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# Templates
Jujutsu supports a functional language to customize output of commands.
The language consists of literals, keywords, operators, functions, and
methods.
A couple of `jj` commands accept a template via `-T`/`--template` option.
## Keywords
Keywords represent objects of different types; the types are described in
a follow-up section.
### Commit keywords
The following keywords can be used in `jj log`/`jj obslog` templates.
* `description: String`
* `change_id: ChangeId`
* `commit_id: CommitId`
* `parents: List<Commit>`
* `author: Signature`
* `committer: Signature`
* `working_copies: String`: For multi-workspace repository, indicate
working-copy commit as `<workspace name>@`.
* `current_working_copy: Boolean`: True for the working-copy commit of the
current workspace.
* `branches: String`
* `tags: String`
* `git_refs: String`
* `git_head: String`
* `divergent: Boolean`: True if the commit's change id corresponds to multiple
visible commits.
* `hidden: Boolean`: True if the commit is not visible (a.k.a. abandoned).
* `conflict: Boolean`: True if the commit contains merge conflicts.
* `empty: Boolean`: True if the commit modifies no files.
* `root: Boolean`: True if the commit is the root commit.
### Operation keywords
The following keywords can be used in `jj op log` templates.
* `current_operation: Boolean`
* `description: String`
* `id: OperationId`
* `tags: String`
* `time: TimestampRange`
* `user: String`
## Operators
The following operators are supported.
* `x.f()`: Method call.
* `x ++ y`: Concatenate `x` and `y` templates.
## Global functions
The following functions are defined.
* `fill(width: Integer, content: Template) -> Template`: Fill lines at
the given `width`.
* `indent(prefix: Template, content: Template) -> Template`: Indent
non-empty lines by the given `prefix`.
* `label(label: Template, content: Template) -> Template`: Apply label to
the content. The `label` is evaluated as a space-separated string.
* `if(condition: Boolean, then: Template[, else: Template]) -> Template`:
Conditionally evaluate `then`/`else` template content.
* `concat(content: Template...) -> Template`:
Same as `content_1 ++ ... ++ content_n`.
* `separate(separator: Template, content: Template...) -> Template`:
Insert separator between **non-empty** contents.
## Types
### Boolean type
No methods are defined. Can be constructed with `false` or `true` literal.
### Commit type
This type cannot be printed. All commit keywords are accessible as 0-argument
methods.
### CommitId / ChangeId type
The following methods are defined.
* `.short([len: Integer]) -> String`
* `.shortest([min_len: Integer]) -> ShortestIdPrefix`: Shortest unique prefix.
### Integer type
No methods are defined.
### List type
A list can be implicitly converted to `Boolean`. The following methods are
defined.
* `.join(separator: Template) -> Template`: Concatenate elements with
the given `separator`.
* `.map(|item| expression) -> ListTemplate`: Apply template `expression`
to each element. Example: `parents.map(|c| c.commit_id().short())`
### ListTemplate type
The following methods are defined. See also the `List` type.
* `.join(separator: Template) -> Template`
### OperationId type
The following methods are defined.
* `.short([len: Integer]) -> String`
### RefName type
The following methods are defined.
* `.name() -> String`: Local branch or tag name.
* `.remote() -> String`: Remote name or empty if this is a local ref.
### ShortestIdPrefix type
The following methods are defined.
* `.prefix() -> String`
* `.rest() -> String`
* `.upper() -> ShortestIdPrefix`
* `.lower() -> ShortestIdPrefix`
### Signature type
The following methods are defined.
* `.name() -> String`
* `.email() -> String`
* `.username() -> String`
* `.timestamp() -> Timestamp`
### String type
A string can be implicitly converted to `Boolean`. The following methods are
defined.
* `.contains(needle: Template) -> Boolean`
* `.first_line() -> String`
* `.lines() -> List<String>`: Split into lines excluding newline characters.
* `.upper() -> String`
* `.lower() -> String`
* `.starts_with(needle: Template) -> Boolean`
* `.ends_with(needle: Template) -> Boolean`
* `.remove_prefix(needle: Template) -> String`: Removes the passed prefix, if present
* `.remove_suffix(needle: Template) -> String`: Removes the passed suffix, if present
* `.substr(start: Integer, end: Integer) -> String`: Extract substring. Negative values count from the end.
#### String literals
String literals must be surrounded by double quotes (`"`). The following escape
sequences starting with a backslash have their usual meaning: `\"`, `\\`, `\n`,
`\r`, `\t`, `\0`. Other escape sequences are not supported. Any UTF-8 characters
are allowed inside a string literal, with two exceptions: unescaped `"`-s and
uses of `\` that don't form a valid escape sequence.
### Template type
Most types can be implicitly converted to `Template`. No methods are defined.
### Timestamp type
The following methods are defined.
* `.ago() -> String`: Format as relative timestamp.
* `.format(format: String) -> String`: Format with [the specified strftime-like
format string](https://docs.rs/chrono/latest/chrono/format/strftime/).
* `.utc() -> Timestamp`: Convert timestamp into UTC timezone.
### TimestampRange type
The following methods are defined.
* `.start() -> Timestamp`
* `.end() -> Timestamp`
* `.duration() -> String`
## Configuration
The default templates and aliases() are defined in the `[templates]` and
`[template-aliases]` sections of the config respectively. The exact definitions
can be seen in the `cli/src/config/templates.toml` file in jj's source tree.
<!--- TODO: Find a way to embed the default config files in the docs -->
New keywords and functions can be defined as aliases, by using any
combination of the predefined keywords/functions and other aliases.
For example:
```toml
[template-aliases]
'commit_change_ids' = '''
concat(
format_field("Commit ID", commit_id),
format_field("Change ID", commit_id),
)
'''
'format_field(key, value)' = 'key ++ ": " ++ value ++ "\n"'
```