From 45391bef0adc510c204b21143caf273e8757eafa Mon Sep 17 00:00:00 2001
From: Don Yin <Don_Yin@outlook.com>
Date: Mon, 26 Oct 2026 12:54:46 +0000
Subject: [PATCH] Install prerequisites into the user library when the default
 is read-only

Fixes #1516

Signed-off-by: Don Yin <Don_Yin@outlook.com>
---
 src/test/suite/util.test.ts | 42 +++++++++++++++++++++++++++++++++++++
 src/util.ts                 | 12 ++++++++++-
 2 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/src/test/suite/util.test.ts b/src/test/suite/util.test.ts
index c9c51f735..f40260d0c 100644
--- a/src/test/suite/util.test.ts
+++ b/src/test/suite/util.test.ts
@@ -1,6 +1,7 @@
 import * as assert from 'assert';
 import cp from 'child_process';
 import { EventEmitter } from 'events';
+import * as fs from 'fs';
 import * as path from 'path';
 import * as os from 'os';
 import * as sinon from 'sinon';
@@ -26,6 +27,47 @@ suite('R command utilities', () => {
         assert.strictEqual(util.ToRStringLiteral('a"b\'c', ''), String.raw`a\"b\'c`);
     });
 
+    test('package installation creates a user library when the default is read-only', async function () {
+        if (process.platform === 'win32' || process.getuid?.() === 0) {
+            this.skip(); // Requires enforced POSIX write permissions.
+        }
+        const root = fs.mkdtempSync(path.join(os.tmpdir(), 'vscode-r-install-'));
+        const library = path.join(root, 'system');
+        const userLibrary = path.join(root, 'user');
+        const profile = path.join(root, '.Rprofile');
+        fs.mkdirSync(library);
+        try {
+            fs.writeFileSync(
+                profile,
+                `
+                .libPaths(${util.ToRStringLiteral(library, "'")}, include.site=FALSE)
+                install.packages <- function(pkgs, lib=.libPaths()[1L], ...) {
+                    stopifnot(pkgs == 'languageserver', dir.exists(lib), lib == Sys.getenv('R_LIBS_USER'))
+                }
+            `,
+            );
+            fs.chmodSync(library, 0o555);
+            sandbox.stub(vscode.window, 'showErrorMessage').resolves('Yes' as never);
+            const task = sandbox
+                .stub(vscode.tasks, 'executeTask')
+                .resolves({} as vscode.TaskExecution);
+            sandbox.stub(vscode.tasks, 'onDidEndTask').returns(new vscode.Disposable(() => {}));
+            await util.promptToInstallRPackage('languageserver', 'lsp.promptToInstall', root);
+            assert.ok(task.calledOnce);
+            const execution = task.firstCall.args[0].execution as vscode.ProcessExecution;
+            const result = cp.spawnSync(execution.process, execution.args, {
+                cwd: root,
+                encoding: 'utf8',
+                env: { ...process.env, R_PROFILE_USER: profile, R_LIBS_USER: userLibrary },
+            });
+            assert.strictEqual(result.status, 0, result.stdout + result.stderr);
+            assert.ok(fs.existsSync(userLibrary));
+        } finally {
+            fs.chmodSync(library, 0o755);
+            fs.rmSync(root, { recursive: true, force: true });
+        }
+    });
+
     test('a failed executable settles with its spawn error', async () => {
         const result = await Promise.race([
             util.spawnAsync(path.join(os.tmpdir(), 'vscode-r-nonexistent-executable')),
diff --git a/src/util.ts b/src/util.ts
index e67a25a63..1b98e2c05 100644
--- a/src/util.ts
+++ b/src/util.ts
@@ -657,7 +657,17 @@ export async function promptToInstallRPackage(
                     '--no-save',
                     '--no-restore',
                     '-e',
-                    `install.packages('${name}', repos='${repo}')`,
+                    `local({
+                        lib <- .libPaths()[1L]
+                        if (file.access(lib, 2L) != 0L) {
+                            lib <- strsplit(Sys.getenv('R_LIBS_USER'), .Platform$path.sep, fixed=TRUE)[[1L]][1L]
+                            if (is.na(lib) || !nzchar(lib) || lib == 'NULL') {
+                                stop('No user R library is configured.')
+                            }
+                            dir.create(lib, recursive=TRUE, showWarnings=FALSE)
+                        }
+                        install.packages(${ToRStringLiteral(name, "'")}, lib=lib, repos=${ToRStringLiteral(repo, "'")})
+                    })`,
                 ];
                 void executeAsTask('Install Package', rPath, args, true);
                 if (postInstallMsg) {