jj log: option to specify preferred id length

The new option is `ui.log-id-preferred-length`. Setting it to 6
is quite convenient for the `jj` repo, for example.

Screenshot: https://user-images.githubusercontent.com/4123047/216535699-ad1e2ac8-73dd-44be-b28a-ebdebc00c63c.png

CHANGELOG.md

@@ -95,6 +95,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   option to `none`. For a presentation that doesn't rely on color, set it to
   `brackets`.
 
+* It is now possible to change the lengths of the ids `jj log` prints with the
+  new `ui.log-id-preferred-length` option.
+
 * `jj print` was renamed to `jj cat`. `jj print` remains as an alias.
   
 * In content that goes to the terminal, the ANSI escape byte (0x1b) is replaced

docs/config.md

@@ -105,7 +105,8 @@ for some examples of what's possible.
 ui.graph.style = "curved"
 ```
 
-### Shortest unique prefixes for ids
+### Display of commit and change ids
+
 ```toml
 ui.unique-prefixes = "brackets"  # Does not rely on color
 ```
@@ -113,6 +114,17 @@ ui.unique-prefixes = "brackets"  # Does not rely on color
 Whether to highlight a unique prefix for commit & change ids. Possible
 values are `styled`, `brackets` and `none` (default: `styled`).
 
+```toml
+ui.log-id-preferred-length = 6
+```
+
+Determines the number of characters displayed for `jj log` for change or commit
+ids. The default is 12. If the `ui.unique-prefixes` option is not set to `none`,
+this option will be ignored if the number of characters it specifies is
+insufficient to print the entire unique prefix of an id.
+
+This option can be convenient to set on a per-repository level.
+
 ### Relative timestamps
 
 ```toml

lib/src/settings.rs

@@ -170,6 +170,13 @@ impl UserSettings {
             .unwrap_or_else(|_| "styled".to_string())
     }
 
+    pub fn log_id_preferred_length(&self) -> Option<usize> {
+        self.config
+            .get_int("ui.log-id-preferred-length")
+            .ok()
+            .and_then(|l| l.try_into().ok())
+    }
+
     pub fn config(&self) -> &config::Config {
         &self.config
     }

src/commands/mod.rs

@@ -1413,12 +1413,13 @@ fn log_template(settings: &UserSettings) -> String {
     } else {
         "committer.timestamp()"
     };
+    let desired_id_len = settings.log_id_preferred_length().unwrap_or(12);
     // TODO: If/when this logic is relevant in the `lib` crate, make this into
     // and enum similar to `ColorChoice`.
     let prefix_format = match settings.unique_prefixes().as_str() {
-        "brackets" => "shortest_prefix_and_brackets()",
-        "styled" => "shortest_styled_prefix()",
-        _ => "short()",
+        "brackets" => format!("shortest_prefix_and_brackets({desired_id_len})"),
+        "styled" => format!("shortest_styled_prefix({desired_id_len})"),
+        _ => format!("short({desired_id_len})"),
     };
     let default_template = format!(
         r#"

src/config-schema.json

@@ -86,7 +86,11 @@
                     "enum": ["none", "brackets", "styled"],
                     "description": "How formatter indicates the unique prefix part of a revision or change ID",
                     "default": "styled"
-
+                },
+                "log-id-preferred-length": {
+                    "type": "integer",
+                    "description": "Determines the number of characters displayed for `jj log` for change or commit ids.",
+                    "default": 12
                 },
                 "editor": {
                     "type": "string",

tests/test_commit_template.rs

@@ -79,11 +79,29 @@ fn test_log_default() {
         &["log", "--config-toml", "ui.unique-prefixes='brackets'"],
     );
     insta::assert_snapshot!(stdout, @r###"
-    @ f[fdaa62087] test.user@example.com 2001-02-03 04:05:09.000 +07:00 my-branch 9d[e54178d5]
+    @ f[fdaa62087a2] test.user@example.com 2001-02-03 04:05:09.000 +07:00 my-branch 9d[e54178d59d]
     | (empty) description 1
-    o 9a[45c67d3e] test.user@example.com 2001-02-03 04:05:08.000 +07:00 4[291e264ae]
+    o 9a[45c67d3e96] test.user@example.com 2001-02-03 04:05:08.000 +07:00 4[291e264ae97]
     | add a file
-    o 0[000000000] 1970-01-01 00:00:00.000 +00:00 0[000000000]
+    o 0[00000000000] 1970-01-01 00:00:00.000 +00:00 0[00000000000]
+      (empty) (no description set)
+    "###);
+    let stdout = test_env.jj_cmd_success(
+        &repo_path,
+        &[
+            "log",
+            "--config-toml",
+            "ui.unique-prefixes='brackets'",
+            "--config-toml",
+            "ui.log-id-preferred-length=2",
+        ],
+    );
+    insta::assert_snapshot!(stdout, @r###"
+    @ f[f] test.user@example.com 2001-02-03 04:05:09.000 +07:00 my-branch 9d
+    | (empty) description 1
+    o 9a test.user@example.com 2001-02-03 04:05:08.000 +07:00 4[2]
+    | add a file
+    o 0[0] 1970-01-01 00:00:00.000 +00:00 0[0]
       (empty) (no description set)
     "###);
 
@@ -105,6 +123,25 @@ fn test_log_default() {
     o 000000000000 1970-01-01 00:00:00.000 +00:00 000000000000
       (empty) (no description set)
     "###);
+    let stdout = test_env.jj_cmd_success(
+        &repo_path,
+        &[
+            "log",
+            "--color=always",
+            "--config-toml",
+            "ui.unique-prefixes='styled'",
+            "--config-toml",
+            "ui.log-id-preferred-length=1",
+        ],
+    );
+    insta::assert_snapshot!(stdout, @r###"
+    @ f test.user@example.com 2001-02-03 04:05:09.000 +07:00 my-branch 9d
+    | (empty) description 1
+    o 9a test.user@example.com 2001-02-03 04:05:08.000 +07:00 4
+    | add a file
+    o 0 1970-01-01 00:00:00.000 +00:00 0
+      (empty) (no description set)
+    "###);
 
     // Test default log output format with prefixes explicitly disabled
     let stdout = test_env.jj_cmd_success(
@@ -119,6 +156,24 @@ fn test_log_default() {
     o 000000000000 1970-01-01 00:00:00.000 +00:00 000000000000
       (empty) (no description set)
     "###);
+    let stdout = test_env.jj_cmd_success(
+        &repo_path,
+        &[
+            "log",
+            "--config-toml",
+            "ui.unique-prefixes='none'",
+            "--config-toml",
+            "ui.log-id-preferred-length=1",
+        ],
+    );
+    insta::assert_snapshot!(stdout, @r###"
+    @ f test.user@example.com 2001-02-03 04:05:09.000 +07:00 my-branch 9
+    | (empty) description 1
+    o 9 test.user@example.com 2001-02-03 04:05:08.000 +07:00 4
+    | add a file
+    o 0 1970-01-01 00:00:00.000 +00:00 0
+      (empty) (no description set)
+    "###);
 
     // Color
     let stdout = test_env.jj_cmd_success(&repo_path, &["log", "--color=always"]);