fix: more error context for missing dep of workspace member

src/cargo/core/workspace.rs

@@ -725,14 +725,15 @@ impl<'cfg> Workspace<'cfg> {
             self.member_ids.insert(pkg.package_id());
             pkg.dependencies()
                 .iter()
-                .map(|d| d.source_id())
-                .filter(|d| d.is_path())
-                .filter_map(|d| d.url().to_file_path().ok())
-                .map(|p| p.join("Cargo.toml"))
+                .map(|d| (d.source_id(), d.package_name()))
+                .filter(|(s, _)| s.is_path())
+                .filter_map(|(s, n)| s.url().to_file_path().ok().map(|p| (p, n)))
+                .map(|(p, n)| (p.join("Cargo.toml"), n))
                 .collect::<Vec<_>>()
         };
-        for candidate in candidates {
-            self.find_path_deps(&candidate, root_manifest, true)
+        for (path, name) in candidates {
+            self.find_path_deps(&path, root_manifest, true)
+                .with_context(|| format!("failed to load manifest for dependency `{}`", name))
                 .map_err(|err| ManifestError::new(err, manifest_path.clone()))?;
         }
         Ok(())

tests/testsuite/workspaces.rs

@@ -2324,6 +2324,55 @@ Caused by:
         .run();
 }
 
+#[cargo_test]
+fn member_dep_missing() {
+    // Make sure errors are not suppressed with -q.
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [project]
+                name = "foo"
+                version = "0.1.0"
+
+                [workspace]
+                members = ["bar"]
+            "#,
+        )
+        .file("src/main.rs", "fn main() {}")
+        .file(
+            "bar/Cargo.toml",
+            r#"
+                [project]
+                name = "bar"
+                version = "0.1.0"
+
+                [dependencies]
+                baz = { path = "baz" }
+            "#,
+        )
+        .file("bar/src/main.rs", "fn main() {}")
+        .build();
+
+    p.cargo("build -q")
+        .with_status(101)
+        .with_stderr(
+            "\
+[ERROR] failed to load manifest for workspace member `[..]/bar`
+
+Caused by:
+  failed to load manifest for dependency `baz`
+
+Caused by:
+  failed to read `[..]foo/bar/baz/Cargo.toml`
+
+Caused by:
+  [..]
+",
+        )
+        .run();
+}
+
 #[cargo_test]
 fn simple_primary_package_env_var() {
     let is_primary_package = r#"