internal: use types to remove some unwraps

crates/project_model/src/manifest_path.rs

@@ -0,0 +1,51 @@
+//! See [`ManifestPath`].
+use std::{convert::TryFrom, ops, path::Path};
+
+use paths::{AbsPath, AbsPathBuf};
+
+/// More or less [`AbsPathBuf`] with non-None parent.
+///
+/// We use it to store path to Cargo.toml, as we frequently use the parent dir
+/// as a working directory to spawn various commands, and its nice to not have
+/// to `.unwrap()` everywhere.
+///
+/// This could have been named `AbsNonRootPathBuf`, as we don't enforce that
+/// this stores manifest files in particular, but we only use this for manifests
+/// at the moment in practice.
+#[derive(Debug, Clone, PartialEq, Eq, Hash, Ord, PartialOrd)]
+pub struct ManifestPath {
+    file: AbsPathBuf,
+}
+
+impl TryFrom<AbsPathBuf> for ManifestPath {
+    type Error = AbsPathBuf;
+
+    fn try_from(file: AbsPathBuf) -> Result<Self, Self::Error> {
+        if file.parent().is_none() {
+            Err(file)
+        } else {
+            Ok(ManifestPath { file })
+        }
+    }
+}
+
+impl ManifestPath {
+    // Shadow `parent` from `Deref`.
+    pub fn parent(&self) -> &AbsPath {
+        self.file.parent().unwrap()
+    }
+}
+
+impl ops::Deref for ManifestPath {
+    type Target = AbsPath;
+
+    fn deref(&self) -> &Self::Target {
+        &*self.file
+    }
+}
+
+impl AsRef<Path> for ManifestPath {
+    fn as_ref(&self) -> &Path {
+        self.file.as_ref()
+    }
+}