Prefer open file contents to disk contents (#1110)

This seems like what we should be doing anyway, but has the benefit that
when using the language service or the debugger in a multi-file project,
then everything just works even if the files haven't been saved to disk
yet.

Putting up early for review, but in initial testing looked to behave as
expected.

vscode/package.json

@@ -397,7 +397,12 @@
           }
         }
       }
-    ]
+    ],
+    "configurationDefaults": {
+      "[qsharp]": {
+        "debug.saveBeforeStart": "none"
+      }
+    }
   },
   "scripts": {
     "build": "npm run tsc:check && node build.mjs",

vscode/src/projectSystem.ts

@@ -53,6 +53,9 @@ async function findManifestDocument(
   // vscode-vfs://github%2B7b2276223a312c22726566223a7b2274797065223a332c226964223a22383439227d7d/microsoft/qsharp/samples/shor.qs
   const currentDocumentUri = URI.parse(currentDocumentUriString);
 
+  // Untitled documents don't have a file location, thus can't have a manifest
+  if (currentDocumentUri.scheme === "untitled") return null;
+
   // just the parent
   // e.g.
   // file://home/foo/bar/src
@@ -64,16 +67,12 @@ async function findManifestDocument(
 
   while (attempts > 0) {
     attempts--;
-    // we abort this check if we are going above the current VS Code
-    // workspace. If the user is working in a multi-root workspace [1],
-    // then we do not perform this check. This is because a multi-
-    // root workspace could contain different roots at different
-    // levels in each others' path ancestry.
-    // [1]: https://code.visualstudio.com/docs/editor/workspaces#_multiroot-workspaces
+
+    // Make sure that the path doesn't go above one of the open workspaces.
     if (
-      vscode.workspace.workspaceFolders?.length === 1 &&
-      Utils.resolvePath(vscode.workspace.workspaceFolders[0].uri, "..") ===
-        uriToQuery
+      !vscode.workspace.workspaceFolders?.some((root) =>
+        uriToQuery.toString().startsWith(root.uri.toString()),
+      )
     ) {
       log.debug("Aborting search for manifest file outside of workspace");
       return null;
@@ -137,6 +136,19 @@ async function readFileUri(
   const uri: vscode.Uri = (maybeUri as any).path
     ? (maybeUri as vscode.Uri)
     : vscode.Uri.parse(maybeUri as string);
+
+  // If any open documents match this uri, return their contents instead of from disk
+  const opendoc = vscode.workspace.textDocuments.find(
+    (opendoc) => opendoc.uri.toString() === uri.toString(),
+  );
+
+  if (opendoc) {
+    return {
+      content: opendoc.getText(),
+      uri,
+    };
+  }
+
   try {
     return await vscode.workspace.fs.readFile(uri).then((res) => {
       return {
@@ -145,7 +157,12 @@ async function readFileUri(
       };
     });
   } catch (_err) {
-    // `readFile` returns `err` if the file didn't exist.
+    // `readFile` should throw the below if the file is not found
+    if (
+      !(_err instanceof vscode.FileSystemError && _err.code === "FileNotFound")
+    ) {
+      log.error("Unexpected error trying to read file", _err);
+    }
     return null;
   }
 }