Fix ark --install on Linux (#712)

Author: lionel-

CHANGELOG.md

@@ -2,10 +2,16 @@
 
 # 0.1.9000
 
+## 2025-02
+
+- Jupyter: The `--install` command now works on Linux (#648).
+
+
 ## 2024-12
 
 - LSP: The statement range provider now has better support for expressions separated by `;` on a single line (posit-dev/positron#4317).
 
+
 ## 2024-11
 
 - LSP: Assignments in function calls (e.g. `list(x <- 1)`) are now detected by the missing symbol linter to avoid annoying false positive diagnostics (https://github.com/posit-dev/positron/issues/3048). The downside is that this causes false negatives when the assignment happens in a call with local scope, e.g. in `local()` or `test_that()`. We prefer to be overly permissive than overly cautious in these matters.
@@ -18,6 +24,7 @@
 
   This solves a number of problems in situations that depend on these variables being defined (https://github.com/posit-dev/positron/issues/3637).
 
+
 ## 2024-10
 
 - Objects assigned at top level are now indexed, in addition to assigned functions. When a name is assigned multiple times, we now only index the first occurrence. This allows you to jump to the first "declaration" of the variable. In the future we'll improve this mechanism so that you can jump to the most recent assignment.

crates/ark/src/interface.rs

@@ -15,7 +15,6 @@ use std::cell::UnsafeCell;
 use std::collections::HashMap;
 use std::ffi::*;
 use std::os::raw::c_uchar;
-use std::path::PathBuf;
 use std::result::Result::Ok;
 use std::sync::Arc;
 use std::sync::Mutex;
@@ -56,7 +55,7 @@ use crossbeam::channel::Receiver;
 use crossbeam::channel::Sender;
 use crossbeam::select;
 use harp::command::r_command;
-use harp::command::r_command_from_path;
+use harp::command::r_home_setup;
 use harp::environment::r_ns_env;
 use harp::environment::Environment;
 use harp::environment::R_ENVS;
@@ -376,28 +375,7 @@ impl RMain {
             args.push(CString::new(arg).unwrap().into_raw());
         }
 
-        let r_home = match std::env::var("R_HOME") {
-            Ok(home) => {
-                // Get `R_HOME` from env var, typically set by Positron / CI / kernel specification
-                PathBuf::from(home)
-            },
-            Err(_) => {
-                // Get `R_HOME` from `PATH`, via `R`
-                let Ok(result) = r_command_from_path(|command| {
-                    command.arg("RHOME");
-                }) else {
-                    panic!("Can't find R or `R_HOME`");
-                };
-
-                let r_home = String::from_utf8(result.stdout).unwrap();
-                let r_home = r_home.trim();
-
-                // Now set `R_HOME`. From now on, `r_command()` can be used to
-                // run exactly the same R as is running in Ark.
-                unsafe { std::env::set_var("R_HOME", r_home) };
-                PathBuf::from(r_home)
-            },
-        };
+        let r_home = r_home_setup();
 
         // `R_HOME` is now defined no matter what and will be used by
         // `r_command()`. Let's discover the other important environment

crates/ark/src/main.rs

@@ -128,7 +128,7 @@ fn main() -> anyhow::Result<()> {
             },
             "--install" => {
                 install_kernel_spec()?;
-                has_action = true;
+                return Ok(());
             },
             "--help" => {
                 print_usage();

crates/ark/src/version.rs

@@ -11,6 +11,7 @@ use std::path::PathBuf;
 
 use anyhow::Context;
 use harp::command::r_command;
+use harp::command::r_home_setup;
 use harp::object::RObject;
 use itertools::Itertools;
 use libr::SEXP;
@@ -31,16 +32,7 @@ pub struct RVersion {
 }
 
 pub fn detect_r() -> anyhow::Result<RVersion> {
-    let output = r_command(|command| {
-        command.arg("RHOME");
-    })
-    .context("Failed to execute R to determine R_HOME")?;
-
-    // Convert the output to a string
-    let r_home = String::from_utf8(output.stdout)
-        .context("Failed to convert R_HOME output to string")?
-        .trim()
-        .to_string();
+    let r_home: String = r_home_setup().to_string_lossy().to_string();
 
     let output = r_command(|command| {
         command

crates/harp/src/command.rs

@@ -18,7 +18,8 @@ use crate::sys::command::COMMAND_R_NAMES;
 /// - For Windows, this looks at `R` (`R.exe`) and `R.bat` (for rig compatibility)
 ///
 /// The executable name is joined to the path in `R_HOME`. If not set, this is a
-/// panic. Use `r_command_from_path()` to exectute R from `PATH` instead.
+/// panic. Use `r_home_setup()` to set `R_HOME` from the R on the `PATH` or use
+/// `r_command_from_path()` to exectute R from `PATH` directly.
 ///
 /// Returns the `Ok()` value of the first success, or the `Err()` value of the
 /// last failure if all locations fail.
@@ -39,6 +40,32 @@ where
     r_command_from_locs(locations, build)
 }
 
+/// Use this before calling `r_command()` to ensure that `R_HOME` is set consistently
+pub fn r_home_setup() -> PathBuf {
+    match std::env::var("R_HOME") {
+        Ok(home) => {
+            // Get `R_HOME` from env var, typically set by Positron / CI / kernel specification
+            PathBuf::from(home)
+        },
+        Err(_) => {
+            // Get `R_HOME` from `PATH`, via `R`
+            let Ok(result) = r_command_from_path(|command| {
+                command.arg("RHOME");
+            }) else {
+                panic!("Can't find R or `R_HOME`");
+            };
+
+            let r_home = String::from_utf8(result.stdout).unwrap();
+            let r_home = r_home.trim();
+
+            // Now set `R_HOME`. From now on, `r_command()` can be used to
+            // run exactly the same R as is running in Ark.
+            unsafe { std::env::set_var("R_HOME", r_home) };
+            PathBuf::from(r_home)
+        },
+    }
+}
+
 /// Execute a `Command` for R found on the `PATH`
 ///
 /// This is like `r_command()` but doesn't assume `R_HOME` is defined.