Make it possible to override the Package Manager URL (#9165)

This commit introduces a new `positron.r.packageManagerRepository`
setting that allows users to override the Posit Package Manager URL used
to install R packages (in some scenarios).

The new setting allows users of self-hosted Package Manager
installations to configure Positron to use them. They also benefit from
our existing logic for determining the appropriate Linux binaries
automatically.

It also opens the door to users pointing at a specific CRAN snapshot on
Public Package Manager rather than `latest`.

Under the hood this works by passing a new flag down to Ark. Companion
PR: posit-dev/ark#906.

### Release Notes


#### New Features

- A new `positron.r.packageManagerRepository` setting allows overriding
the Posit Package Manager URL used to install R packages when
`positron.r.defaultRepositories` is set to `auto`.

#### Bug Fixes

- N/A

### QA Notes

Please advise.

Signed-off-by: Aaron Jacobs <[email protected]>

Author: atheriel

extensions/positron-r/package.json

@@ -349,6 +349,11 @@
             ],
             "default": "auto",
             "markdownDescription": "%r.configuration.defaultRepositories.description%"
+          },
+          "positron.r.packageManagerRepository": {
+            "scope": "window",
+            "type": "string",
+            "markdownDescription": "%r.configuration.packageManagerRepository.description%"
           }
         }
       }

extensions/positron-r/package.nls.json

@@ -70,6 +70,7 @@
 	"r.configuration.defaultRepositories.rstudio.description": "Use the RStudio CRAN mirror (cran.rstudio.com)",
 	"r.configuration.defaultRepositories.posit-ppm.description": "Use the Posit public package manager (packagemanager.posit.co)",
 	"r.configuration.defaultRepositories.none.description": "Do not set a default repository or change the value of the 'repos' option",
+	"r.configuration.packageManagerRepository.description": "The Posit Package Manager repository URL to use for R package installation, rather than the default https://packagemanager.posit.co/cran/latest.\n\nOnly takes effect when `#positron.r.defaultRepositories#` is `auto` (restart Positron to apply).",
 	"r.walkthrough.migrateFromRStudio.title": "Migrating from RStudio to Positron",
 	"r.walkthrough.migrateFromRStudio.description": "Learn how to get started with R in Positron as an RStudio user!",
 	"r.walkthrough.migrateFromRStudio.panesAndUI.title": "Get to know the Positron UI",

extensions/positron-r/src/kernel-spec.ts

@@ -84,12 +84,18 @@ export function createJupyterKernelSpec(
 
 	// Set the default repositories
 	const defaultRepos = config.get<string>('defaultRepositories') ?? 'auto';
+	const ppmRepo = config.get<string>('packageManagerRepository');
 	if (defaultRepos === 'auto') {
 		const reposConf = findReposConf();
 		if (reposConf) {
 			// If there's a `repos.conf` file in a well-known directory, use
 			// that.
 			argv.push(...['--repos-conf', reposConf]);
+		} else if (ppmRepo) {
+			// If the user has specified a custom Package Manager URL, use it
+			//
+			// Note: Ark can't handle trailing slashes, so strip them here
+			argv.push(...['--default-ppm-repo', ppmRepo.endsWith('/') ? ppmRepo.slice(0, -1) : ppmRepo]);
 		} else if (vscode.env.uiKind === vscode.UIKind.Web) {
 			// No repos.conf; if we're web mode use Posit's Public Package
 			// Manager
@@ -99,6 +105,23 @@ export function createJupyterKernelSpec(
 		// `--default-repos` at all, and let Ark choose an appropriate
 		// repository (usually `cran.rstudio.com)
 	} else {
+		// Warn the user about inconsistent PPM settings.
+		if (ppmRepo) {
+			const openSettings = vscode.l10n.t('Open Settings');
+			// Note: we don't `await` here to avoid stalling the kernel startup.
+			vscode.window.showWarningMessage(
+				vscode.l10n.t('The "Package Manager Repository" setting is ignored unless "Default Repositories" is set to "auto".'),
+				{ title: openSettings },
+				{ title: vscode.l10n.t('Dismiss'), isCloseAffordance: true },
+			).then((action) => {
+				if (action?.title === openSettings) {
+					vscode.commands.executeCommand(
+						'workbench.action.openSettings',
+						'positron.r.defaultRepositories'
+					);
+				}
+			});
+		}
 		// The remaining options map directly to Ark's `--default-repos`
 		// command line option
 		argv.push(...['--default-repos', defaultRepos]);