Add --init subcommand (#541)

When `--init` is passed on the command line, search upward for the
project root, identified by the presence of a VCS directory like `.git`,
falling back to the current directory, and create a default justfile in
that directory.

tests/init.rs

@@ -0,0 +1,159 @@
+use std::{fs, process::Command};
+
+use executable_path::executable_path;
+
+use test_utilities::{tempdir, tmptree};
+
+const EXPECTED: &str = "default:\n\techo 'Hello, world!'\n";
+
+#[test]
+fn current_dir() {
+  let tmp = tempdir();
+
+  let output = Command::new(executable_path("just"))
+    .current_dir(tmp.path())
+    .arg("--init")
+    .output()
+    .unwrap();
+
+  assert!(output.status.success());
+
+  assert_eq!(
+    fs::read_to_string(tmp.path().join("justfile")).unwrap(),
+    EXPECTED
+  );
+}
+
+#[test]
+fn exists() {
+  let tmp = tempdir();
+
+  let output = Command::new(executable_path("just"))
+    .current_dir(tmp.path())
+    .arg("--init")
+    .output()
+    .unwrap();
+
+  assert!(output.status.success());
+
+  let output = Command::new(executable_path("just"))
+    .current_dir(tmp.path())
+    .arg("--init")
+    .output()
+    .unwrap();
+
+  assert!(!output.status.success());
+}
+
+#[test]
+fn invocation_directory() {
+  let tmp = tmptree! {
+    ".git": {},
+  };
+
+  let output = Command::new(executable_path("just"))
+    .current_dir(tmp.path())
+    .arg("--init")
+    .output()
+    .unwrap();
+
+  assert!(output.status.success());
+
+  assert_eq!(
+    fs::read_to_string(tmp.path().join("justfile")).unwrap(),
+    EXPECTED
+  );
+}
+
+#[test]
+fn alternate_marker() {
+  let tmp = tmptree! {
+    "_darcs": {},
+  };
+
+  let output = Command::new(executable_path("just"))
+    .current_dir(tmp.path())
+    .arg("--init")
+    .output()
+    .unwrap();
+
+  assert!(output.status.success());
+
+  assert_eq!(
+    fs::read_to_string(tmp.path().join("justfile")).unwrap(),
+    EXPECTED
+  );
+}
+
+#[test]
+fn search_directory() {
+  let tmp = tmptree! {
+    sub: {
+      ".git": {},
+    },
+  };
+
+  let output = Command::new(executable_path("just"))
+    .current_dir(tmp.path())
+    .arg("--init")
+    .arg("sub/")
+    .output()
+    .unwrap();
+
+  assert!(output.status.success());
+
+  assert_eq!(
+    fs::read_to_string(tmp.path().join("sub/justfile")).unwrap(),
+    EXPECTED
+  );
+}
+
+#[test]
+fn justfile() {
+  let tmp = tmptree! {
+    sub: {
+      ".git": {},
+    },
+  };
+
+  let output = Command::new(executable_path("just"))
+    .current_dir(tmp.path().join("sub"))
+    .arg("--init")
+    .arg("--justfile")
+    .arg(tmp.path().join("justfile"))
+    .output()
+    .unwrap();
+
+  assert!(output.status.success());
+
+  assert_eq!(
+    fs::read_to_string(tmp.path().join("justfile")).unwrap(),
+    EXPECTED
+  );
+}
+
+#[test]
+fn justfile_and_working_directory() {
+  let tmp = tmptree! {
+    sub: {
+      ".git": {},
+    },
+  };
+
+  let output = Command::new(executable_path("just"))
+    .current_dir(tmp.path().join("sub"))
+    .arg("--init")
+    .arg("--justfile")
+    .arg(tmp.path().join("justfile"))
+    .arg("--working-directory")
+    .arg("/")
+    .output()
+    .unwrap();
+
+  assert!(output.status.success());
+
+  assert_eq!(
+    fs::read_to_string(tmp.path().join("justfile")).unwrap(),
+    EXPECTED
+  );
+}