feat(unstable): add DENO_NODE_CONDITIONS env var (#29848)

Follow up to https://github.com/denoland/deno/pull/29586 that
adds a `DENO_NODE_CONDITIONS` env var that allows to
specify conditional exports when the user can't control
CLI flags passed to the command (eg. on Deploy).

cli/args/flags.rs

@@ -4577,6 +4577,7 @@ fn lock_args() -> [Arg; 3] {
 fn node_conditions_arg() -> Arg {
   Arg::new("unstable-node-conditions")
     .long("unstable-node-conditions")
+    .help("Use this argument to specify custom conditions for npm package exports. You can also use DENO_NODE_CONDITIONS env var.")
     .use_value_delimiter(true)
     .action(ArgAction::Append)
 }

cli/main.rs

@@ -548,6 +548,14 @@ fn resolve_flags_and_init(
 
   load_env_variables_from_env_file(flags.env_file.as_ref(), flags.log_level);
   flags.unstable_config.fill_with_env();
+  if flags.node_conditions.is_empty() {
+    if let Ok(conditions) = std::env::var("DENO_NODE_CONDITIONS") {
+      flags.node_conditions = conditions
+        .split(",")
+        .map(|c| c.trim().to_string())
+        .collect();
+    }
+  }
 
   let otel_config = flags.otel_config();
   init_logging(flags.log_level, Some(otel_config.clone()));

tests/specs/run/conditional_exports/__test__.jsonc

@@ -13,6 +13,14 @@
       "args": "run --unstable-node-conditions react-server -A main.js",
       "output": "condition.out",
       "exitCode": 1
+    },
+    {
+      "args": "run -A main.js",
+      "envs": {
+        "DENO_NODE_CONDITIONS": "react-server"
+      },
+      "output": "condition.out",
+      "exitCode": 1
     }
   ]
 }