Ensure R doesn't run the .Rprofile on Windows (#581)

crates/ark/src/sys/windows/interface.rs

@@ -20,6 +20,7 @@ use libr::R_DefParamsEx;
 use libr::R_HomeDir;
 use libr::R_SetParams;
 use libr::R_SignalHandlers;
+use libr::Rboolean_FALSE;
 use stdext::cargs;
 
 use crate::interface::r_busy;
@@ -69,6 +70,12 @@ pub fn setup_r(mut _args: Vec<*mut c_char>) {
         (*params).R_Interactive = 1;
         (*params).CharacterMode = libr::UImode_RGui;
 
+        // Never load the user or site `.Rprofile`s during `setup_Rmainloop()`.
+        // We do it for the user once ark is ready. We faithfully reimplement
+        // R's behavior for finding these files in `startup.rs`.
+        (*params).LoadInitFile = Rboolean_FALSE;
+        (*params).LoadSiteFile = Rboolean_FALSE;
+
         (*params).WriteConsole = None;
         (*params).WriteConsoleEx = Some(r_write_console);
         (*params).ReadConsole = Some(r_read_console);

crates/ark/tests/r-profile-once.rs

@@ -0,0 +1,50 @@
+use std::io::Write;
+
+use amalthea::fixtures::dummy_frontend::ExecuteRequestOptions;
+use ark::fixtures::DummyArkFrontendRprofile;
+
+// SAFETY:
+// Do not write any other tests related to `.Rprofile` in
+// this integration test file. We can only start R up once
+// per process, so we can only run one `.Rprofile`. Use a
+// separate integration test (i.e. separate process) if you
+// need to test more details related to `.Rprofile` usage.
+
+/// See https://github.com/posit-dev/positron/issues/4253
+#[test]
+fn test_r_profile_is_only_run_once() {
+    // The trailing `\n` is critical, otherwise R's `source()` silently fails
+    let contents = r#"
+if (exists("x")) {
+  x <- 2
+} else {
+  x <- 1
+}
+
+"#;
+
+    // Write `contents` to a tempfile that we declare to be
+    // the `.Rprofile` that R should use
+    let mut file = tempfile::NamedTempFile::new().unwrap();
+    write!(file, "{contents}").unwrap();
+
+    let path = file.path();
+    let path = path.to_str().unwrap();
+
+    unsafe { std::env::set_var("R_PROFILE_USER", path) };
+
+    // Ok, start R. If we've set everything correctly, R should not run
+    // the `.Rprofile`, but ark should - i.e. it should run exactly 1 time.
+    let frontend = DummyArkFrontendRprofile::lock();
+
+    frontend.send_execute_request("x", ExecuteRequestOptions::default());
+    frontend.recv_iopub_busy();
+
+    let input = frontend.recv_iopub_execute_input();
+    assert_eq!(input.code, "x");
+    assert_eq!(frontend.recv_iopub_execute_result(), "[1] 1");
+
+    frontend.recv_iopub_idle();
+
+    assert_eq!(frontend.recv_shell_execute_reply(), input.execution_count);
+}