Introduce support for user-provided extensions

This change introduces support for discovering and executing
user-provided extensions to the program. Extensions are useful for
allowing users to provide additional functionality on top of the
nitrocli proper. Implementation wise we stick to an approach similar to
git or cargo subcommands in nature: we search the directories listed in
the PATH environment variable for a file that starts with "nitrocli-",
followed by the extension name. This file is then executed. It is
assumed that the extension recognizes (or at least not prohibits) the
following arguments: --nitrocli (providing the path to the nitrocli
binary), --model (with the model passed to the main program), and
--verbosity (the verbosity level).

1 files changed, 43 insertions, 0 deletions

diff --git a/src/tests/extensions.rs b/src/tests/extensions.rs
new file mode 100644
index 0000000..a295949
--- /dev/null
+++ b/src/tests/extensions.rs
@@ -0,0 +1,43 @@
+// extensions.rs
+
+// Copyright (C) 2020 The Nitrocli Developers
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+use std::env;
+use std::fs;
+
+use super::*;
+
+#[test]
+fn resolve_extensions() -> anyhow::Result<()> {
+  let dir1 = tempfile::tempdir()?;
+  let dir2 = tempfile::tempdir()?;
+
+  {
+    let ext1_path = dir1.path().join("nitrocli-ext1");
+    let ext2_path = dir1.path().join("nitrocli-ext2");
+    let ext3_path = dir2.path().join("nitrocli-super-1337-extensions111one");
+    let _ext1 = fs::File::create(&ext1_path)?;
+    let _ext2 = fs::File::create(&ext2_path)?;
+    let _ext3 = fs::File::create(&ext3_path)?;
+
+    let path = env::join_paths(&[dir1.path(), dir2.path()])?;
+    assert_eq!(
+      crate::commands::resolve_extension(&path, ffi::OsStr::new("ext1"))?,
+      ext1_path
+    );
+    assert_eq!(
+      crate::commands::resolve_extension(&path, ffi::OsStr::new("ext2"))?,
+      ext2_path
+    );
+    assert_eq!(
+      crate::commands::resolve_extension(&path, ffi::OsStr::new("super-1337-extensions111one"))?,
+      ext3_path
+    );
+
+    let err = crate::commands::resolve_extension(&ffi::OsStr::new(""), ffi::OsStr::new("ext1"))
+      .unwrap_err();
+    assert_eq!(err.to_string(), "Extension nitrocli-ext1 not found");
+  }
+  Ok(())
+}