fix(lsp): manifest resolver always reports "Failed to download"

Problem:
Manifest resolver always reports:

    Failed to download latest "…" manifest. Falling back to local manifest.

Solution:
In `fetchRemoteManifest()`, if the ETag indicates no new manifest is
needed, return the local manifest instead of throwing an error

Author: justinmk3

packages/core/src/shared/lsp/baseLspInstaller.ts

@@ -52,7 +52,9 @@ export abstract class BaseLspInstaller<T extends ResourcePaths = ResourcePaths,
         await this.postInstall(assetDirectory)
 
         const deletedVersions = await cleanLspDownloads(manifest.versions, nodePath.dirname(assetDirectory))
-        this.logger.debug(`cleaning old LSP versions deleted ${deletedVersions.length} versions`)
+        if (deletedVersions.length > 0) {
+            this.logger.debug(`cleaning old LSP versions: deleted ${deletedVersions.length} versions`)
+        }
 
         const r = {
             ...installationResult,

packages/core/src/shared/lsp/lspResolver.ts

@@ -73,7 +73,7 @@ export class LanguageServerResolver {
          * ```
          */
         const resolved = await tryStageResolvers('getServer', serverResolvers, getServerVersion)
-        logger.info('Finished updating "%s" LSP server: %O', this.lsName, resolved.assetDirectory)
+        logger.info('Finished preparing "%s" LSP server: %O', this.lsName, resolved.assetDirectory)
         return resolved
     }
 

packages/core/src/shared/lsp/manifestResolver.ts

@@ -64,25 +64,38 @@ export class ManifestResolver {
         }).getNewETagContent(this.getEtag())
 
         if (!resp.content) {
-            throw new ToolkitError(
-                `New content was not downloaded; fallback to the locally stored "${this.lsName}" manifest`
-            )
+            const msg = `"${this.lsName}" manifest unchanged, skipping download: ${this.manifestURL}`
+            logger.debug(msg)
+
+            const localManifest = await this.getLocalManifest(true).catch(() => undefined)
+            if (localManifest) {
+                localManifest.location = 'remote'
+                return localManifest
+            } else {
+                // Will emit a `languageServer_setup` result=failed metric...
+                throw new ToolkitError(msg)
+            }
         }
 
+        logger.debug(`fetched "${this.lsName}" manifest: ${this.manifestURL}`)
         const manifest = this.parseManifest(resp.content)
         await this.saveManifest(resp.eTag, resp.content)
         await this.checkDeprecation(manifest)
         manifest.location = 'remote'
         return manifest
     }
 
-    private async getLocalManifest(): Promise<Manifest> {
-        logger.info(`Failed to download latest "${this.lsName}" manifest. Falling back to local manifest.`)
+    private async getLocalManifest(silent: boolean = false): Promise<Manifest> {
+        if (!silent) {
+            logger.info(`trying local "${this.lsName}" manifest...`)
+        }
         const storage = this.getStorage()
         const manifestData = storage[this.lsName]
 
         if (!manifestData?.content) {
-            throw new ToolkitError(`Failed to download "${this.lsName}" manifest and no local manifest found.`)
+            const msg = `local "${this.lsName}" manifest not found`
+            logger.warn(msg)
+            throw new ToolkitError(msg)
         }
 
         const manifest = this.parseManifest(manifestData.content)
@@ -145,6 +158,7 @@ export class ManifestResolver {
             ...storage,
             [this.lsName]: {
                 etag,
+                // XXX: this stores the entire manifest. vscode warns about our globalStorage size...
                 content,
             },
         })

packages/core/src/shared/resourcefetcher/httpResourceFetcher.ts

@@ -68,9 +68,9 @@ export class HttpResourceFetcher implements ResourceFetcher<Response> {
         if (response.status === 304) {
             // Explanation: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/If-None-Match
             contents = undefined
-            this.logger.verbose(`E-Tag, ${eTagResponse}, matched. No content downloaded from: ${this.url}`)
+            this.logger.verbose(`E-Tag matched (${eTagResponse}). Download skipped: ${this.url}`)
         } else {
-            this.logger.verbose(`No E-Tag match. Downloaded content from: ${this.logText()}`)
+            this.logger.verbose(`E-Tag not matched. Downloaded: ${this.logText()}`)
         }
 
         return { content: contents, eTag: eTagResponse }