feat: set usage arguments and flags as environment variables for toml tasks (#4159)

Fixes #4070

@jdx I have tested it locally and everything seems to work fine, but
before merging the PR I would like to have your opinion if everything
seems ok. After that, I would like to add some e2e tests, but I do not
know whether it is better to add them to e2e/tasks/test_task_run_toml,
e2e/tasks/test_task_vars or to create a new test file just for this
feature. Where do you think it is best to add them?

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

e2e/tasks/test_task_run_toml

@@ -44,3 +44,26 @@ arg "myarg" "myarg description" default="foo"
 run = 'echo {{arg(name="myarg")}}'
 EOF
 assert "mise run a" "foo"
+
+cat <<'EOF' >mise.toml
+[tasks.usage-env]
+usage = '''
+arg "myarg" "myarg description" default="foo"
+'''
+run = 'echo myarg=$usage_myarg'
+EOF
+
+assert "mise run usage-env" "myarg=foo"
+assert "mise run usage-env bar" "myarg=bar"
+
+cat <<'EOF' >mise.toml
+[tasks.usage-env]
+usage = '''
+flag "-m --myflag <myflag>" default="foo"
+'''
+run = 'echo myflag=$usage_myflag'
+EOF
+
+assert "mise run usage-env" "myflag=foo"
+assert "mise run usage-env -m bar" "myflag=bar"
+assert "mise run usage-env --myflag bar" "myflag=bar"

src/cli/run.rs

@@ -471,6 +471,8 @@ impl Run {
             for (script, args) in
                 task.render_run_scripts_with_args(self.cd.clone(), &task.args, &env)?
             {
+                let get_args = || task.run.iter().chain(task.args.iter()).cloned().collect();
+                self.parse_usage_spec_and_init_env(task, &mut env, get_args)?;
                 self.exec_script(&script, &args, task, &env, &prefix)?;
             }
         }
@@ -585,14 +587,8 @@ impl Run {
         let mut env = env.clone();
         let command = file.to_string_lossy().to_string();
         let args = task.args.iter().cloned().collect_vec();
-        let (spec, _) = task.parse_usage_spec(self.cd.clone(), &env)?;
-        if !spec.cmd.args.is_empty() || !spec.cmd.flags.is_empty() {
-            let args = once(command.clone()).chain(args.clone()).collect_vec();
-            let po = usage::parse(&spec, &args).map_err(|err| eyre!(err))?;
-            for (k, v) in po.as_env() {
-                env.insert(k, v);
-            }
-        }
+        let get_args = || once(command.clone()).chain(args.clone()).collect_vec();
+        self.parse_usage_spec_and_init_env(task, &mut env, get_args)?;
 
         if !self.quiet(Some(task)) {
             let cmd = format!("{} {}", display_path(file), args.join(" "))
@@ -606,6 +602,24 @@ impl Run {
         self.exec(file, &args, task, &env, prefix)
     }
 
+    fn parse_usage_spec_and_init_env(
+        &self,
+        task: &Task,
+        env: &mut EnvMap,
+        get_args: impl Fn() -> Vec<String>,
+    ) -> Result<()> {
+        let (spec, _) = task.parse_usage_spec(self.cd.clone(), env)?;
+        if !spec.cmd.args.is_empty() || !spec.cmd.flags.is_empty() {
+            let args: Vec<String> = get_args();
+            let po = usage::parse(&spec, &args).map_err(|err| eyre!(err))?;
+            for (k, v) in po.as_env() {
+                env.insert(k, v);
+            }
+        }
+
+        Ok(())
+    }
+
     fn exec(
         &self,
         file: &Path,