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README.md

@@ -320,7 +320,7 @@ 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. The unstable
-mode can also be set using the environment variable `JUST_ALLOW_UNSTABLE=true` (any other value for the variable besides `true` is treated as false).
+mode can also be set using the environment variable `JUST_UNSTABLE`; any value for this variable other than "false", "0", or the empty string will be treated as enabling unstable mode.
 
 
 Editor Support

src/config.rs

@@ -3,8 +3,6 @@ use {
   clap::{App, AppSettings, Arg, ArgGroup, ArgMatches, ArgSettings},
 };
 
-pub(crate) const UNSTABLE_KEY: &str = "JUST_ALLOW_UNSTABLE";
-
 // These three strings should be kept in sync:
 pub(crate) const CHOOSER_DEFAULT: &str = "fzf --multi --preview 'just --show {}'";
 pub(crate) const CHOOSER_ENVIRONMENT_KEY: &str = "JUST_CHOOSER";
@@ -572,7 +570,9 @@ impl Config {
     };
 
     let unstable = matches.is_present(arg::UNSTABLE)
-      || std::env::var_os(UNSTABLE_KEY).map_or(false, |val| val.to_string_lossy() == "true");
+      || std::env::var_os("JUST_UNSTABLE").map_or(false, |val| {
+        !["false", "0", ""].contains(&val.to_string_lossy().as_ref())
+      });
 
     Ok(Self {
       check: matches.is_present(arg::CHECK),

tests/unstable.rs

@@ -6,25 +6,44 @@ fn set_unstable_true_with_env_var() {
 default:
     echo 'foo'
   "#;
-  Test::new()
+
+  for val in ["true", "some-arbitrary-string"] {
+    Test::new()
+      .justfile(justfile)
+      .args(["--dump", "--dump-format", "json"])
+      .env("JUST_UNSTABLE", val)
+      .status(EXIT_SUCCESS)
+      .stdout_regex("*")
+      .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(["--dump", "--dump-format", "json"])
-    .env("JUST_ALLOW_UNSTABLE", "true")
-    .status(EXIT_SUCCESS)
-    .stdout_regex("*")
+    .env("JUST_UNSTABLE", val)
+    .status(EXIT_FAILURE)
+    .stderr("error: The JSON dump format is currently unstable. Invoke `just` with the `--unstable` flag to enable unstable features.\n")
     .run();
+  }
 }
 
 #[test]
-fn set_unstable_false_with_env_var() {
+fn set_unstable_false_with_env_var_unset() {
   let justfile = r#"
 default:
     echo 'foo'
   "#;
   Test::new()
     .justfile(justfile)
     .args(["--dump", "--dump-format", "json"])
-    .env("JUST_ALLOW_UNSTABLE", "false")
     .status(EXIT_FAILURE)
     .stderr("error: The JSON dump format is currently unstable. Invoke `just` with the `--unstable` flag to enable unstable features.\n")
     .run();