Avoid errors in read-only GitHub sources (#1787)

This is an incremental improvement for viewing GitHub sources that
avoids treating them as open documents since they are read-only buffers.
In the future, we can do the work to associate them with the existing
compilation taht contains those sources so that things like hover and
goto-def work, but for now those code paths are user-code specific and
need some reworking to handle navigation in a compile unit for a
dependency.

compiler/qsc_project/src/lib.rs

@@ -23,5 +23,5 @@ pub use manifest::{Manifest, ManifestDescriptor, PackageRef, PackageType, MANIFE
 pub use project::FileSystemAsync;
 pub use project::{
     key_for_package_ref, package_ref_from_key, DependencyCycle, DirEntry, EntryType, Error,
-    FileSystem, PackageCache, PackageGraphSources, PackageInfo, Project,
+    FileSystem, PackageCache, PackageGraphSources, PackageInfo, Project, GITHUB_SCHEME,
 };

compiler/qsc_project/src/project.rs

@@ -18,6 +18,8 @@ use std::{
 };
 use thiserror::Error;
 
+pub const GITHUB_SCHEME: &str = "qsharp-github-source";
+
 /// Describes a Q# project with all its sources and dependencies resolved.
 #[derive(Debug, Clone)]
 pub struct Project {
@@ -414,7 +416,7 @@ pub trait FileSystemAsync {
         let manifest = serde_json::from_str::<Manifest>(&manifest_content).map_err(|e| {
             Error::GitHubManifestParse {
                 path: format!(
-                    "qsharp-github-source:{}/{}/{}{}/qsharp.json",
+                    "{GITHUB_SCHEME}:{}/{}/{}{}/qsharp.json",
                     dep.owner,
                     dep.repo,
                     dep.r#ref,
@@ -448,7 +450,7 @@ pub trait FileSystemAsync {
             // and open them using cached contents.
             sources.push((
                 format!(
-                    "qsharp-github-source:{}/{}/{}{path}",
+                    "{GITHUB_SCHEME}:{}/{}/{}{path}",
                     dep.owner, dep.repo, dep.r#ref
                 )
                 .into(),

language_service/src/state.rs

@@ -417,6 +417,12 @@ impl<'a> CompilationStateUpdater<'a> {
                         // a less confusing user experience.
                         continue;
                     }
+                    if uri.starts_with(qsc_project::GITHUB_SCHEME) {
+                        // Don't publish diagnostics for GitHub URIs.
+                        // This is temporary workaround to avoid spurious errors when a document
+                        // is opened in single file mode that is part of a read-only GitHub project.
+                        continue;
+                    }
 
                     self.publish_diagnostics_for_doc(state, &uri, errors);
                 }