feat(unstable/fmt): move yaml formatting behind unstable flag (#24848)

This moves YAML formatting behind an unstable flag for Deno 1.46. This
will make it opt-in to start and then we can remove the flag to make it
on by default in version of Deno after that.

This can be specified by doing `deno fmt --unstable-yaml` or by
specifying the following in a deno.json file:

```json
{
  "unstable": ["fmt-yaml"]
}
```

4 files changed, 32 insertions, 1 deletions

diff --git a/tests/integration/fmt_tests.rs b/tests/integration/fmt_tests.rs
index 17adef6f8..dab2b2ce4 100644
--- a/tests/integration/fmt_tests.rs
+++ b/tests/integration/fmt_tests.rs
@@ -49,6 +49,7 @@ fn fmt_test() {
     .current_dir(&testdata_fmt_dir)
     .args_vec(vec![
       "fmt".to_string(),
+      "--unstable-yaml".to_string(),
       format!(
         "--ignore={badly_formatted_js},{badly_formatted_md},{badly_formatted_json},{badly_formatted_yaml},{badly_formatted_ipynb}",
       ),
@@ -69,6 +70,7 @@ fn fmt_test() {
     .args_vec(vec![
       "fmt".to_string(),
       "--check".to_string(),
+      "--unstable-yaml".to_string(),
       badly_formatted_js.to_string(),
       badly_formatted_md.to_string(),
       badly_formatted_json.to_string(),
@@ -86,6 +88,7 @@ fn fmt_test() {
     .current_dir(&testdata_fmt_dir)
     .args_vec(vec![
       "fmt".to_string(),
+      "--unstable-yaml".to_string(),
       badly_formatted_js.to_string(),
       badly_formatted_md.to_string(),
       badly_formatted_json.to_string(),
diff --git a/tests/integration/upgrade_tests.rs b/tests/integration/upgrade_tests.rs
index 844401d4e..6af73f65f 100644
--- a/tests/integration/upgrade_tests.rs
+++ b/tests/integration/upgrade_tests.rs
@@ -145,7 +145,7 @@ fn upgrade_with_out_in_tmpdir() {
   assert!(v.contains("1.11.5"));
 }
 
-#[test]
+#[flaky_test::flaky_test]
 fn upgrade_invalid_stable_version() {
   let context = upgrade_context();
   let temp_dir = context.temp_dir();
diff --git a/tests/specs/fmt/unstable_yaml/__test__.jsonc b/tests/specs/fmt/unstable_yaml/__test__.jsonc
new file mode 100644
index 000000000..885db59b9
--- /dev/null
+++ b/tests/specs/fmt/unstable_yaml/__test__.jsonc
@@ -0,0 +1,25 @@
+{
+  "tempDir": true,
+  "tests": {
+    "nothing": {
+      "args": "fmt",
+      "output": "Checked 1 file\n"
+    },
+    "flag": {
+      "args": "fmt --unstable-yaml",
+      "output": "[WILDLINE]badly_formatted.yml\nChecked 1 file\n"
+    },
+    "config_file": {
+      "steps": [{
+        "args": [
+          "eval",
+          "Deno.writeTextFile('deno.json', '{\\n  \"unstable\": [\"fmt-yaml\"]\\n}\\n')"
+        ],
+        "output": "[WILDCARD]"
+      }, {
+        "args": "fmt",
+        "output": "[WILDLINE]badly_formatted.yml\nChecked 2 files\n"
+      }]
+    }
+  }
+}
\ No newline at end of file
diff --git a/tests/specs/fmt/unstable_yaml/badly_formatted.yml b/tests/specs/fmt/unstable_yaml/badly_formatted.yml
new file mode 100644
index 000000000..49646f320
--- /dev/null
+++ b/tests/specs/fmt/unstable_yaml/badly_formatted.yml
@@ -0,0 +1,3 @@
+- Test
+ - Test
+  - Test
\ No newline at end of file