Add a built-in for setting the PPM repo in a running session

crates/ark/src/modules/positron/repos.R

@@ -39,3 +39,34 @@ apply_repo_defaults <- function(
     }
     options(repos = repos)
 }
+
+#' Set the Posit Package Manager repository
+#'
+#' Sets the Posit Package Manager repository URL for the current session. The
+#' URL will be processed to point to a Linux distribution-specific binary URL if
+#' applicable.
+#'
+#' This function only overrides the CRAN repository when Ark has previously set
+#' it or when it uses placeholder `"@CRAN@"`.
+#'
+#' @param url A PPM repository URL. Must be in the form
+#'   `"https://host/repo/snapshot"`, e.g.,
+#'   `"https://packagemanager.posit.co/cran/latest"`.
+#'
+#' @return `NULL`, invisibly.
+#'
+#' @export
+.ps.setPPMRepo <- function(url) {
+    # Use Ark's built-in PPM binary URL detection.
+    url <- .ps.Call("ps_get_ppm_binary_url", url)
+
+    # If Ark has already set the repos option, it should be safe to do so again.
+    repos <- getOption("repos")
+    if (isTRUE(attr(repos, "IDE"))) {
+        repos[["CRAN"]] <- url
+        return(options(repos = repos))
+    }
+
+    # Otherwise we defer to the existing application logic.
+    apply_repo_defaults(c(CRAN = url))
+}

crates/ark/src/repos.rs

@@ -13,9 +13,11 @@ use std::io::BufRead;
 use std::io::BufReader;
 use std::path::PathBuf;
 
+use anyhow::Context;
 use harp::exec::RFunction;
 use harp::exec::RFunctionExt;
 use harp::RObject;
+use libr::SEXP;
 
 use crate::modules::ARK_ENVS;
 
@@ -346,6 +348,28 @@ fn get_ppm_binary_package_repo(repo_url: Option<url::Url>) -> String {
     }
 }
 
+#[harp::register]
+pub extern "C-unwind" fn ps_get_ppm_binary_url(url: SEXP) -> anyhow::Result<SEXP> {
+    let url_string = unsafe { RObject::view(url).to::<String>().context("`url` must be a string")? };
+    if url_string.is_empty() {
+        return Err(anyhow::anyhow!("Empty Package Manager URL provided"));
+    }
+
+    // Validate the PPM URL structure.
+    let parsed = url::Url::parse(&url_string).context("Invalid URL format")?;
+    let segments = parsed
+        .path_segments()
+        .ok_or_else(|| anyhow::anyhow!("Package Manager URL must have a path"))?;
+    if segments.count() != 2 {
+        return Err(anyhow::anyhow!(
+            "Package Manager URL must have exactly 2 path segments (e.g., /cran/latest)"
+        ));
+    }
+
+    let final_url = get_ppm_binary_package_repo(Some(parsed));
+    Ok(RObject::from(final_url).sexp)
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;