cli `fix`: change default from `-s @` to `-s 'reachable(@, mutable())'`

Most of the value of `jj fix` over a shell script is in formatting commits
other than `@`. `@::` often doesn't contain those other commits, so `-s @` is a
bad default.

We could get the same effect from `-s 'mutable() & ::@'`, but `reachable()` is
a bit more explicit and simple to read.

We could also base this on excluding `trunk()`, but that just seems like an
indirection for `mutable()` that might ignore the user's intent if they have
configured part of trunk to be mutable.

CHANGELOG.md

···
 * Dropped support for automatic upgrade of repo formats used by versions before
   0.12.0.
 
+* `jj fix` now defaults to the broader revset `-s reachable(@, mutable())`
+  instead of `-s @`.
+
 ### Deprecations
 
 ### New features

cli/src/commands/fix.rs

···
 pub(crate) struct FixArgs {
     /// Fix files in the specified revision(s) and their descendants. If no
     /// revisions are specified, this defaults to the `revsets.fix` setting, or
-    /// `@` if it is not set.
+    /// `reachable(@, mutable())` if it is not set.
     #[arg(long, short)]
     source: Vec<RevisionArg>,
     /// Fix only these paths

cli/src/config-schema.json

···
                 "fix": {
                     "type": "string",
                     "description": "Default set of revisions to fix when no explicit revset is given for jj fix",
-                    "default": "@"
+                    "default": "reachable(@, mutable())"
                 },
                 "log": {
                     "type": "string",

cli/src/config/revsets.toml

···
 # adding/updating any of these aliases
 
 [revsets]
-fix = "@"
+fix = "reachable(@, mutable())"
 log = "@ | ancestors(immutable_heads().., 2) | trunk()"
 
 [revset-aliases]

cli/tests/cli-reference@.md.snap

···
 
 ###### **Options:**
 
-* `-s`, `--source <SOURCE>` — Fix files in the specified revision(s) and their descendants. If no revisions are specified, this defaults to the `revsets.fix` setting, or `@` if it is not set
+* `-s`, `--source <SOURCE>` — Fix files in the specified revision(s) and their descendants. If no revisions are specified, this defaults to the `revsets.fix` setting, or `reachable(@, mutable())` if it is not set
 
 
 

cli/tests/test_fix_command.rs

···
 #[test]
 fn test_default_revset() {
     let (test_env, repo_path) = init_with_fake_formatter(&["--uppercase"]);
+    std::fs::write(repo_path.join("file"), "trunk1").unwrap();
+    test_env.jj_cmd_ok(&repo_path, &["branch", "create", "trunk1"]);
+    test_env.jj_cmd_ok(&repo_path, &["new"]);
+    std::fs::write(repo_path.join("file"), "trunk2").unwrap();
+    test_env.jj_cmd_ok(&repo_path, &["branch", "create", "trunk2"]);
+    test_env.jj_cmd_ok(&repo_path, &["new", "trunk1"]);
     std::fs::write(repo_path.join("file"), "foo").unwrap();
     test_env.jj_cmd_ok(&repo_path, &["branch", "create", "foo"]);
+    test_env.jj_cmd_ok(&repo_path, &["new", "trunk1"]);
+    std::fs::write(repo_path.join("file"), "bar1").unwrap();
+    test_env.jj_cmd_ok(&repo_path, &["branch", "create", "bar1"]);
     test_env.jj_cmd_ok(&repo_path, &["new"]);
-    std::fs::write(repo_path.join("file"), "bar").unwrap();
-    test_env.jj_cmd_ok(&repo_path, &["branch", "create", "bar"]);
-    test_env.jj_cmd_ok(&repo_path, &["new", "foo"]);
-    std::fs::write(repo_path.join("file"), "baz").unwrap();
-    test_env.jj_cmd_ok(&repo_path, &["branch", "create", "baz"]);
+    std::fs::write(repo_path.join("file"), "bar2").unwrap();
+    test_env.jj_cmd_ok(&repo_path, &["branch", "create", "bar2"]);
+    test_env.jj_cmd_ok(&repo_path, &["new"]);
+    std::fs::write(repo_path.join("file"), "bar3").unwrap();
+    test_env.jj_cmd_ok(&repo_path, &["branch", "create", "bar3"]);
+    test_env.jj_cmd_ok(&repo_path, &["edit", "bar2"]);
 
-    // With no args and no revset configuration, we fix `@`.
+    // With no args and no revset configuration, we fix `reachable(@, mutable())`,
+    // which includes bar{1,2,3} and excludes trunk{1,2} (which is immutable) and
+    // foo (which is mutable but not reachable).
+    test_env.add_config(r#"revset-aliases."immutable_heads()" = "trunk2""#);
     let (stdout, stderr) = test_env.jj_cmd_ok(&repo_path, &["fix"]);
     insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"
-    Fixed 1 commits of 1 checked.
-    Working copy now at: mzvwutvl 5205c5f1 baz | (no description set)
-    Parent commit      : qpvuntsm 34af74d0 foo | (no description set)
+    Fixed 3 commits of 3 checked.
+    Working copy now at: yostqsxw 0bd830d2 bar2 | (no description set)
+    Parent commit      : yqosqzyt 4747dd17 bar1 | (no description set)
     Added 0 files, modified 1 files, removed 0 files
     "###);
+    let content = test_env.jj_cmd_success(&repo_path, &["print", "file", "-r", "trunk1"]);
+    insta::assert_snapshot!(content, @"trunk1");
+    let content = test_env.jj_cmd_success(&repo_path, &["print", "file", "-r", "trunk2"]);
+    insta::assert_snapshot!(content, @"trunk2");
     let content = test_env.jj_cmd_success(&repo_path, &["print", "file", "-r", "foo"]);
     insta::assert_snapshot!(content, @"foo");
-    let content = test_env.jj_cmd_success(&repo_path, &["print", "file", "-r", "bar"]);
-    insta::assert_snapshot!(content, @"bar");
-    let content = test_env.jj_cmd_success(&repo_path, &["print", "file", "-r", "baz"]);
-    insta::assert_snapshot!(content, @"BAZ");
+    let content = test_env.jj_cmd_success(&repo_path, &["print", "file", "-r", "bar1"]);
+    insta::assert_snapshot!(content, @"BAR1");
+    let content = test_env.jj_cmd_success(&repo_path, &["print", "file", "-r", "bar2"]);
+    insta::assert_snapshot!(content, @"BAR2");
+    let content = test_env.jj_cmd_success(&repo_path, &["print", "file", "-r", "bar3"]);
+    insta::assert_snapshot!(content, @"BAR3");
 }
 
 #[test]
···
     std::fs::write(repo_path.join("file"), "bar").unwrap();
     test_env.jj_cmd_ok(&repo_path, &["branch", "create", "bar"]);
 
-    // Check out a different commit so that the schema default `@` would behave
-    // differently from our customized default.
+    // Check out a different commit so that the schema default `reachable(@,
+    // mutable())` would behave differently from our customized default.
     test_env.jj_cmd_ok(&repo_path, &["new", "-r", "foo"]);
     test_env.add_config(r#"revsets.fix = "bar""#);