Allow --unstable to be set with an environment variable

README.md

@@ -325,7 +325,8 @@ This does not, however, preclude fixing outright bugs, even if doing so might br
 
 There will never be a `just` 2.0. Any desirable backwards-incompatible changes will be opt-in on a per-`justfile` basis, so users may migrate at their leisure.
 
-Features that aren't yet ready for stabilization are gated behind the `--unstable` flag. Features enabled by `--unstable` may change in backwards incompatible ways at any time.
+Features that aren't yet ready for stabilization are gated behind the `--unstable` flag. Features enabled by `--unstable` may change in backwards incompatible ways at any time. Unstable features can also be enabled by setting the environment variable `JUST_UNSTABLE` to any value other than `false`, `0`, or the empty string.
+
 
 Editor Support
 --------------

src/config.rs

@@ -569,6 +569,11 @@ impl Config {
       None
     };
 
+    let unstable = matches.is_present(arg::UNSTABLE)
+      || std::env::var_os("JUST_UNSTABLE")
+        .map(|val| !(val == "false" || val == "0" || val.is_empty()))
+        .unwrap_or_default();
+
     Ok(Self {
       check: matches.is_present(arg::CHECK),
       dry_run: matches.is_present(arg::DRY_RUN),
@@ -578,7 +583,7 @@ impl Config {
       load_dotenv: !matches.is_present(arg::NO_DOTENV),
       shell_command: matches.is_present(arg::SHELL_COMMAND),
       unsorted: matches.is_present(arg::UNSORTED),
-      unstable: matches.is_present(arg::UNSTABLE),
+      unstable,
       list_heading: matches
         .value_of(arg::LIST_HEADING)
         .unwrap_or("Available recipes:\n")

tests/lib.rs

@@ -87,6 +87,7 @@ mod string;
 mod subsequents;
 mod tempdir;
 mod undefined_variables;
+mod unstable;
 #[cfg(target_family = "windows")]
 mod windows_shell;
 mod working_directory;

tests/test.rs

@@ -234,7 +234,7 @@ impl Test {
 
     if let Some(ref stdout_regex) = self.stdout_regex {
       if !stdout_regex.is_match(output_stdout) {
-        panic!("Stdout regex mismatch:\n{output_stderr:?}\n!~=\n/{stdout_regex:?}/");
+        panic!("Stdout regex mismatch:\n{output_stdout:?}\n!~=\n/{stdout_regex:?}/");
       }
     }
 

tests/unstable.rs

@@ -0,0 +1,50 @@
+use super::*;
+
+#[test]
+fn set_unstable_true_with_env_var() {
+  let justfile = r#"
+default:
+    echo 'foo'
+  "#;
+
+  for val in ["true", "some-arbitrary-string"] {
+    Test::new()
+      .justfile(justfile)
+      .args(["--fmt"])
+      .env("JUST_UNSTABLE", val)
+      .status(EXIT_SUCCESS)
+      .stderr_regex("Wrote justfile to `.*`\n")
+      .run();
+  }
+}
+
+#[test]
+fn set_unstable_false_with_env_var() {
+  let justfile = r#"
+default:
+    echo 'foo'
+  "#;
+  for val in ["0", "", "false"] {
+    Test::new()
+    .justfile(justfile)
+    .args(["--fmt"])
+    .env("JUST_UNSTABLE", val)
+    .status(EXIT_FAILURE)
+    .stderr("error: The `--fmt` command is currently unstable. Invoke `just` with the `--unstable` flag to enable unstable features.\n")
+    .run();
+  }
+}
+
+#[test]
+fn set_unstable_false_with_env_var_unset() {
+  let justfile = r#"
+default:
+    echo 'foo'
+  "#;
+  Test::new()
+    .justfile(justfile)
+    .args(["--fmt"])
+    .status(EXIT_FAILURE)
+    .stderr("error: The `--fmt` command is currently unstable. Invoke `just` with the `--unstable` flag to enable unstable features.\n")
+    .run();
+}