ROVER-245 Fix two small buglets

The first is that we weren't supplying the correct content root
for the supergraph.yaml. The second is that we need to have a
value of the routing URLm, even if it's not used, when it goes to the
supergraph.yaml

src/command/lsp/mod.rs

@@ -78,6 +78,7 @@ async fn run_lsp(client_config: StudioClientConfig, lsp_opts: LspOpts) -> RoverR
             }
         })
         .ok_or_else(|| anyhow!("Could not find supergraph.yaml file."))?;
+    let supergraph_content_root = supergraph_yaml_path.parent().unwrap().to_path_buf();
 
     let studio_client = client_config.get_authenticated_client(&lsp_opts.plugin_opts.profile)?;
 
@@ -90,18 +91,13 @@ async fn run_lsp(client_config: StudioClientConfig, lsp_opts: LspOpts) -> RoverR
             Some(&FileDescriptorType::File(supergraph_yaml_path.clone())),
         )?;
     let lazily_resolved_supergraph_config = supergraph_config
-        .lazily_resolve_subgraphs(&supergraph_yaml_path)
+        .lazily_resolve_subgraphs(&supergraph_content_root)
         .await?;
 
-    let root_uri = supergraph_yaml_path
-        .parent()
-        .map(|path| path.to_string())
-        .unwrap_or_default();
-
     // Build the service to spin up the language server
     let (service, socket, _receiver) = ApolloLanguageServer::build_service(
         Config {
-            root_uri,
+            root_uri: supergraph_content_root.to_string(),
             enable_auto_composition: false,
             force_federation: false,
             disable_telemetry: false,

src/composition/supergraph/config/resolve/mod.rs

@@ -299,7 +299,10 @@ impl From<FullyResolvedSubgraphs> for SupergraphConfig {
             (
                 name,
                 SubgraphConfig {
-                    routing_url: None,
+                    // This value is effectively unused but has to be set to something that
+                    // is not "null" when serialised otherwise the supergraph binary
+                    // complains
+                    routing_url: Some(String::from("localhost")),
                     schema: SchemaSource::Sdl { sdl },
                 },
             )

src/composition/supergraph/config/resolve/subgraph.rs

@@ -28,6 +28,8 @@ pub enum ResolveSubgraphError {
         supergraph_config_path: Utf8PathBuf,
         /// Supplied path to the subgraph schema file
         path: PathBuf,
+        /// The result of joining the paths together, that caused the failure
+        joined_path: PathBuf,
         /// The source error
         source: std::io::Error,
     },
@@ -97,6 +99,7 @@ impl UnresolvedSubgraph {
                 subgraph_name: self.name.to_string(),
                 supergraph_config_path: root.clone(),
                 path: path.as_std_path().to_path_buf(),
+                joined_path: joined_path.as_std_path().to_path_buf(),
                 source: err,
             }),
         }