cli: print hint about defining jj co alias to avoid warning

It can take a while to get used to the slightly different mental model
of `jj new` if you're used to `git/hg checkout`. Let's help users
define an alias to avoid the warning `jj checkout` currently prints. I
think users will still slowly get used to running `jj new` instead of
`jj checkout`. I think this patch might just make that process slower
(bad) and less frustrating (good).

cli/src/commands/checkout.rs

@@ -45,7 +45,11 @@ pub(crate) fn cmd_checkout(
         ui.warning(),
         "warning: `jj checkout` is deprecated; use `jj new` instead, which is equivalent"
     )?;
-    let mut workspace_command = command.workspace_helper(ui)?;
+    writeln!(
+        ui.hint(),
+        r#"Run e.g. `jj config set --user aliases.co '["new"]'` to disable this message."#
+    )?;
+let mut workspace_command = command.workspace_helper(ui)?;
     let target = workspace_command.resolve_single_rev(&args.revision)?;
     let mut tx = workspace_command.start_transaction();
     let commit_builder = tx

cli/tests/test_checkout.rs

@@ -30,6 +30,7 @@ fn test_checkout() {
     insta::assert_snapshot!(stdout, @"");
     insta::assert_snapshot!(stderr, @r###"
     warning: `jj checkout` is deprecated; use `jj new` instead, which is equivalent
+    Run e.g. `jj config set --user aliases.co '["new"]'` to disable this message.
     Working copy now at: zsuskuln 05ce7118 (empty) (no description set)
     Parent commit      : rlvkpnrz 5c52832c (empty) second
     "###);
@@ -66,6 +67,7 @@ fn test_checkout_not_single_rev() {
     let stderr = test_env.jj_cmd_failure(&repo_path, &["checkout", "root()..@"]);
     insta::assert_snapshot!(stderr, @r###"
     warning: `jj checkout` is deprecated; use `jj new` instead, which is equivalent
+    Run e.g. `jj config set --user aliases.co '["new"]'` to disable this message.
     Error: Revset "root()..@" resolved to more than one revision
     Hint: The revset "root()..@" resolved to these revisions:
     royxmykx 2f859371 (empty) (no description set)
@@ -79,6 +81,7 @@ fn test_checkout_not_single_rev() {
     let stderr = test_env.jj_cmd_failure(&repo_path, &["checkout", "root()..@-"]);
     insta::assert_snapshot!(stderr, @r###"
     warning: `jj checkout` is deprecated; use `jj new` instead, which is equivalent
+    Run e.g. `jj config set --user aliases.co '["new"]'` to disable this message.
     Error: Revset "root()..@-" resolved to more than one revision
     Hint: The revset "root()..@-" resolved to these revisions:
     mzvwutvl 5c1afd8b (empty) fifth
@@ -91,6 +94,7 @@ fn test_checkout_not_single_rev() {
     let stderr = test_env.jj_cmd_failure(&repo_path, &["checkout", "@-|@--"]);
     insta::assert_snapshot!(stderr, @r###"
     warning: `jj checkout` is deprecated; use `jj new` instead, which is equivalent
+    Run e.g. `jj config set --user aliases.co '["new"]'` to disable this message.
     Error: Revset "@-|@--" resolved to more than one revision
     Hint: The revset "@-|@--" resolved to these revisions:
     mzvwutvl 5c1afd8b (empty) fifth
@@ -100,6 +104,7 @@ fn test_checkout_not_single_rev() {
     let stderr = test_env.jj_cmd_failure(&repo_path, &["checkout", "none()"]);
     insta::assert_snapshot!(stderr, @r###"
     warning: `jj checkout` is deprecated; use `jj new` instead, which is equivalent
+    Run e.g. `jj config set --user aliases.co '["new"]'` to disable this message.
     Error: Revset "none()" didn't resolve to any revisions
     "###);
 }