Add r_command() for executing commands over R and R.bat (#599)

* Add `r_command()` for executing commands over `R` and `R.bat`

* Rework `r_command()` for readability

crates/ark/src/interface.rs

@@ -53,6 +53,7 @@ use crossbeam::channel::unbounded;
 use crossbeam::channel::Receiver;
 use crossbeam::channel::Sender;
 use crossbeam::select;
+use harp::command::r_command;
 use harp::environment::r_ns_env;
 use harp::environment::Environment;
 use harp::environment::R_ENVS;
@@ -355,12 +356,14 @@ impl RMain {
             args.push(CString::new(arg).unwrap().into_raw());
         }
 
-        // Get `R_HOME`, typically set by Positron / CI / kernel specification
+        // Get `R_HOME` from env var, typically set by Positron / CI / kernel specification
         let r_home = match std::env::var("R_HOME") {
             Ok(home) => PathBuf::from(home),
             Err(_) => {
-                // Get `R_HOME` from `PATH`, via R
-                let Ok(result) = std::process::Command::new("R").arg("RHOME").output() else {
+                // Get `R_HOME` from `PATH`, via `R`
+                let Ok(result) = r_command(|command| {
+                    command.arg("RHOME");
+                }) else {
                     panic!("Can't find R or `R_HOME`");
                 };
                 let r_home = String::from_utf8(result.stdout).unwrap();

crates/ark/src/version.rs

@@ -8,9 +8,9 @@
 use std::collections::HashMap;
 use std::env;
 use std::path::PathBuf;
-use std::process::Command;
 
 use anyhow::Context;
+use harp::command::r_command;
 use harp::object::RObject;
 use itertools::Itertools;
 use libr::SEXP;
@@ -31,24 +31,25 @@ pub struct RVersion {
 }
 
 pub fn detect_r() -> anyhow::Result<RVersion> {
-    let output = Command::new("R")
-        .arg("RHOME")
-        .output()
-        .context("Failed to execute R to determine R_HOME")?;
+    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 output = Command::new("R")
-        .arg("--vanilla")
-        .arg("-s")
-        .arg("-e")
-        .arg("cat(version$major, \".\", version$minor, sep = \"\")")
-        .output()
-        .context("Failed to execute R to determine version number")?;
+    let output = r_command(|command| {
+        command
+            .arg("--vanilla")
+            .arg("-s")
+            .arg("-e")
+            .arg("cat(version$major, \".\", version$minor, sep = \"\")");
+    })
+    .context("Failed to execute R to determine version number")?;
 
     let version = String::from_utf8(output.stdout)
         .context("Failed to convert R version number to a string")?

crates/harp/src/command.rs

@@ -0,0 +1,49 @@
+//
+// command.rs
+//
+// Copyright (C) 2024 Posit Software, PBC. All rights reserved.
+//
+//
+
+use std::io;
+use std::process::Command;
+use std::process::Output;
+
+use crate::sys::command::COMMAND_R_LOCATIONS;
+
+/// Execute a `Command` for R, trying multiple locations where R might exist
+///
+/// - For unix, this look at `R`
+/// - For Windows, this looks at `R` (`R.exe`) and `R.bat` (for rig compatibility)
+///
+/// Returns the `Ok()` value of the first success, or the `Err()` value of the
+/// last failure if all locations fail.
+pub fn r_command<F>(build: F) -> io::Result<Output>
+where
+    F: Fn(&mut Command),
+{
+    assert!(COMMAND_R_LOCATIONS.len() > 0);
+
+    let mut out = None;
+
+    for program in COMMAND_R_LOCATIONS.iter() {
+        // Build the `Command` from the user's function
+        let mut command = Command::new(program);
+        build(&mut command);
+
+        // Run it, waiting on it to finish.
+        // Store it as `out` no matter what. If all locations fail
+        // we end up returning the last failure.
+        let result = command.output();
+        let ok = result.is_ok();
+        out = Some(result);
+
+        if ok {
+            // We had a successful command, don't try any more
+            break;
+        }
+    }
+
+    // SAFETY: The `assert!` above ensures at least 1 program location is provided
+    out.unwrap()
+}

crates/harp/src/fixtures/mod.rs

@@ -10,14 +10,14 @@
 
 use std::os::raw::c_char;
 use std::path::PathBuf;
-use std::process::Command;
 use std::sync::Once;
 
 use libr::setup_Rmainloop;
 use libr::R_CStackLimit;
 use libr::Rf_initialize_R;
 use stdext::cargs;
 
+use crate::command::r_command;
 use crate::library::RLibraries;
 use crate::R_MAIN_THREAD_ID;
 
@@ -53,7 +53,10 @@ pub fn r_test_init() {
         let r_home = match std::env::var("R_HOME") {
             Ok(r_home) => PathBuf::from(r_home),
             Err(_) => {
-                let result = Command::new("R").arg("RHOME").output().unwrap();
+                let result = r_command(|command| {
+                    command.arg("RHOME");
+                })
+                .expect("Can't locate R to determine `R_HOME`.");
                 let r_home = String::from_utf8(result.stdout).unwrap();
                 let r_home = r_home.trim();
                 unsafe { std::env::set_var("R_HOME", r_home) };

crates/harp/src/lib.rs

@@ -6,6 +6,7 @@
 //
 pub mod attrib;
 pub mod call;
+pub mod command;
 pub mod data_frame;
 pub mod environment;
 pub mod environment_iter;

crates/harp/src/sys/unix.rs

@@ -5,6 +5,7 @@
  *
  */
 
+pub mod command;
 pub mod library;
 pub mod line_ending;
 pub mod polled_events;

crates/harp/src/sys/unix/command.rs

@@ -0,0 +1,9 @@
+/*
+ * command.rs
+ *
+ * Copyright (C) 2024 Posit Software, PBC. All rights reserved.
+ *
+ */
+
+/// Locations on the `PATH` to look for R when using `Command::new()`
+pub(crate) const COMMAND_R_LOCATIONS: [&str; 1] = ["R"];

crates/harp/src/sys/windows.rs

@@ -5,6 +5,7 @@
  *
  */
 
+pub mod command;
 pub mod library;
 pub mod line_ending;
 mod locale;

crates/harp/src/sys/windows/command.rs

@@ -0,0 +1,9 @@
+/*
+ * command.rs
+ *
+ * Copyright (C) 2024 Posit Software, PBC. All rights reserved.
+ *
+ */
+
+/// Locations on the `PATH` to look for R when using `Command::new()`
+pub(crate) const COMMAND_R_LOCATIONS: [&str; 2] = ["R", "R.bat"];