Allow \0 escape for nulls

This allows safely getting e.g. multiple descriptions, and knowing where the
boundaries are

CHANGELOG.md

@@ -20,6 +20,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * `jj op log` now supports `--no-graph`.
 
+* Templates now support an additional escape: `\0`. This will output a literal
+  null byte. This may be useful for e.g.
+  `jj log -T 'description ++ "\0"' --no-graph` to output descriptions only, but
+  be able to tell where the boundaries are
+
 ### Fixed bugs
 
 ## [0.9.0] - 2023-09-06

cli/src/template.pest

@@ -19,7 +19,7 @@
 
 whitespace = _{ " " | "\t" | "\r" | "\n" | "\x0c" }
 
-escape = @{ "\\" ~ ("t" | "r" | "n" | "\"" | "\\") }
+escape = @{ "\\" ~ ("t" | "r" | "n" | "0" | "\"" | "\\") }
 literal_char = @{ !("\"" | "\\") ~ ANY }
 raw_literal = @{ literal_char+ }
 literal = { "\"" ~ (raw_literal | escape)* ~ "\"" }

cli/src/template_parser.rs

@@ -256,12 +256,13 @@ fn parse_string_literal(pair: Pair<Rule>) -> String {
             Rule::raw_literal => {
                 result.push_str(part.as_str());
             }
-            Rule::escape => match part.as_str().as_bytes()[1] as char {
-                '"' => result.push('"'),
-                '\\' => result.push('\\'),
-                't' => result.push('\t'),
-                'r' => result.push('\r'),
-                'n' => result.push('\n'),
+            Rule::escape => match &part.as_str()[1..] {
+                "\"" => result.push('"'),
+                "\\" => result.push('\\'),
+                "t" => result.push('\t'),
+                "r" => result.push('\r'),
+                "n" => result.push('\n'),
+                "0" => result.push('\0'),
                 char => panic!("invalid escape: \\{char:?}"),
             },
             _ => panic!("unexpected part of string: {part:?}"),
@@ -963,8 +964,8 @@ mod tests {
     fn test_string_literal() {
         // "\<char>" escapes
         assert_eq!(
-            parse_into_kind(r#" "\t\r\n\"\\" "#),
-            Ok(ExpressionKind::String("\t\r\n\"\\".to_owned())),
+            parse_into_kind(r#" "\t\r\n\"\\\0" "#),
+            Ok(ExpressionKind::String("\t\r\n\"\\\0".to_owned())),
         );
 
         // Invalid "\<char>" escape

cli/tests/test_log_command.rs

@@ -314,6 +314,42 @@ fn test_log_with_or_without_diff() {
     "###);
 }
 
+#[test]
+fn test_log_null_terminate_multiline_descriptions() {
+    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,
+        &["commit", "-m", "commit 1 line 1", "-m", "commit 1 line 2"],
+    );
+    test_env.jj_cmd_success(
+        &repo_path,
+        &["commit", "-m", "commit 2 line 1", "-m", "commit 2 line 2"],
+    );
+    test_env.jj_cmd_success(
+        &repo_path,
+        &["describe", "-m", "commit 3 line 1", "-m", "commit 3 line 2"],
+    );
+
+    let stdout = test_env.jj_cmd_success(
+        &repo_path,
+        &[
+            "log",
+            "-r",
+            "~root()",
+            "-T",
+            r#"description ++ "\0""#,
+            "--no-graph",
+        ],
+    );
+    insta::assert_debug_snapshot!(
+        stdout,
+        @r###""commit 3 line 1\n\ncommit 3 line 2\n\0commit 2 line 1\n\ncommit 2 line 2\n\0commit 1 line 1\n\ncommit 1 line 2\n\0""###
+    )
+}
+
 #[test]
 fn test_log_shortest_accessors() {
     let test_env = TestEnvironment::default();

cli/tests/test_operations.rs

@@ -146,6 +146,27 @@ fn test_op_log_no_graph() {
     "###);
 }
 
+#[test]
+fn test_op_log_no_graph_null_terminated() {
+    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, &["commit", "-m", "message1"]);
+    test_env.jj_cmd_success(&repo_path, &["commit", "-m", "message2"]);
+
+    let stdout = test_env.jj_cmd_success(
+        &repo_path,
+        &[
+            "op",
+            "log",
+            "--no-graph",
+            "--template",
+            r#"id.short(4) ++ "\0""#,
+        ],
+    );
+    insta::assert_debug_snapshot!(stdout, @r###""c8b0\07277\019b8\0f1c4\0""###);
+}
+
 #[test]
 fn test_op_log_template() {
     let test_env = TestEnvironment::default();

cli/tests/test_templater.rs

@@ -279,6 +279,8 @@ fn test_templater_list_method() {
 
     insta::assert_snapshot!(render(r#""".lines().join("|")"#), @"");
     insta::assert_snapshot!(render(r#""a\nb\nc".lines().join("|")"#), @"a|b|c");
+    // Null separator
+    insta::assert_snapshot!(render(r#""a\nb\nc".lines().join("\0")"#), @"a\0b\0c");
     // Keyword as separator
     insta::assert_snapshot!(render(r#""a\nb\nc".lines().join(commit_id.short(2))"#), @"a00b00c");