Merge #3053

3053: Feature: downloading lsp server from GitHub r=matklad a=Veetaha

This is currently very WIP, I may need to change this and that, add "download language server command", logging stuff (for future bug reports), etc., but it already works.
Also didn't test this on windows yet and mac (don't have the latter)

The quirks:
* Downloaded binary doesn't have executable permissions by default, that's why we ~~`chmod 111`~~ (**[UPD]** `chmod 755` as per @lnicola [suggestion](https://github.com/rust-analyzer/rust-analyzer/pull/3053#discussion_r376694456)) for it.
* To remove installed binary run `rm /${HOME}/.config/Code/User/globalStorage/matklad.rust-analyzer/ra_lsp_server-linux`, ~~note that `-f` flag is necessary, because of `111` permissions (I think this should be changed)~~ (**[UPD]** --force is no longer needed due to 755 permissions).

I also tried to keep things simple and not to use too many dependencies, all the ones added have 0 dependencies, (`ts-not-nil` is my personal npm package, that imitates `unwrap()` in TypeScript)

**[UPD]** I reduced throttle latency of progress indicator to 200ms for smoother UX


// TODO:
- [x] ~~Add `Rust Analyzer: Download latest language server` vscode command.~~ **[UPD]**: having reviewed the code and estimated available options I concluded that this feature requires too many code changes, I'd like to extract this into a separate PR after we merge this one.
- [x] Add some logging for future debugging
- [x] ~~Gracefully handle the case when language server is not available (e.g. no internet connection, user explicitly rejected the download, etc.)~~ **[UPD]** Decided to postpone better implementation of graceful degradation logic as per [conversation](https://rust-lang.zulipchat.com/#narrow/stream/185405-t-compiler.2Fwg-rls-2.2E0/topic/Deployment.20and.20installation/near/187758550).

Demo (**[UPD]** this is a bit outdated, but still mainly reflects the feature):
![ra-github-release-download-mvp](https://user-images.githubusercontent.com/36276403/74077961-4f248a80-4a2d-11ea-962f-27c650fd6c4c.gif)

Related issue: #2988 #3007 

Co-authored-by: Veetaha <[email protected]>
Co-authored-by: Veetaha <[email protected]>

1 files changed, 55 insertions, 0 deletions

diff --git a/editors/code/src/installation/interfaces.ts b/editors/code/src/installation/interfaces.ts
new file mode 100644
index 000000000..8039d0b90
--- /dev/null
+++ b/editors/code/src/installation/interfaces.ts
@@ -0,0 +1,55 @@
+export interface GithubRepo {
+    name: string;
+    owner: string;
+}
+
+/**
+ * Metadata about particular artifact retrieved from GitHub releases.
+ */
+export interface ArtifactMetadata {
+    releaseName: string;
+    downloadUrl: string;
+}
+
+/**
+ * Represents the source of a binary artifact which is either specified by the user
+ * explicitly, or bundled by this extension from GitHub releases.
+ */
+export type BinarySource = BinarySource.ExplicitPath | BinarySource.GithubRelease;
+
+export namespace BinarySource {
+    /**
+     * Type tag for `BinarySource` discriminated union.
+     */
+    export const enum Type { ExplicitPath, GithubRelease }
+
+    export interface ExplicitPath {
+        type: Type.ExplicitPath;
+
+        /**
+         * Filesystem path to the binary specified by the user explicitly.
+         */
+        path: string;
+    }
+
+    export interface GithubRelease {
+        type: Type.GithubRelease;
+
+        /**
+         * Repository where the binary is stored.
+         */
+        repo: GithubRepo;
+
+        /**
+         * Directory on the filesystem where the bundled binary is stored.
+         */
+        dir: string;
+
+        /**
+         * Name of the binary file. It is stored under the same name on GitHub releases
+         * and in local `.dir`.
+         */
+        file: string;
+    }
+
+}