Make get_executor fallible and fail on invalid value

src/diskio/mod.rs

@@ -59,6 +59,7 @@ use std::io::{self, Write};
 use std::path::{Path, PathBuf};
 use std::time::{Duration, Instant};
 
+use crate::errors::{ErrorKind, Result, ResultExt};
 use crate::process;
 use crate::utils::notifications::Notification;
 
@@ -194,21 +195,16 @@ pub fn create_dir<P: AsRef<Path>>(path: P) -> io::Result<()> {
 /// Get the executor for disk IO.
 pub fn get_executor<'a>(
     notify_handler: Option<&'a dyn Fn(Notification<'_>)>,
-) -> Box<dyn Executor + 'a> {
+) -> Result<Box<dyn Executor + 'a>> {
     // If this gets lots of use, consider exposing via the config file.
-    let thread_count = match process()
-        .var("RUSTUP_IO_THREADS")
-        .map(|x| x.parse::<usize>())
-    {
-        Ok(Ok(n)) => n,
-        Ok(Err(_)) => {
-            eprintln!("Invalid value for RUSTUP_IO_THREADS. Has to be an integer");
-            num_cpus::get()
-        }
+    let thread_count = match process().var("RUSTUP_IO_THREADS") {
         Err(_) => num_cpus::get(),
+        Ok(n) => n
+            .parse::<usize>()
+            .chain_err(|| ErrorKind::InvalidIoThreadsCount)?,
     };
     match thread_count {
-        0 | 1 => Box::new(immediate::ImmediateUnpacker::new()),
-        thread_count => Box::new(threaded::Threaded::new(notify_handler, thread_count)),
+        0 | 1 => Ok(Box::new(immediate::ImmediateUnpacker::new())),
+        n => Ok(Box::new(threaded::Threaded::new(notify_handler, n))),
     }
 }

src/dist/component/package.rs

@@ -293,7 +293,7 @@ fn unpack_without_first_dir<'a, R: Read>(
     path: &Path,
     notify_handler: Option<&'a dyn Fn(Notification<'_>)>,
 ) -> Result<()> {
-    let mut io_executor: Box<dyn Executor> = get_executor(notify_handler);
+    let mut io_executor: Box<dyn Executor> = get_executor(notify_handler)?;
     let entries = archive
         .entries()
         .chain_err(|| ErrorKind::ExtractingPackage)?;

src/errors.rs

@@ -375,6 +375,9 @@ error_chain! {
         BrokenPartialFile {
             description("partially downloaded file may have been damaged and was removed, please try again")
         }
+        InvalidIoThreadsCount {
+            description("invalid value in RUSTUP_IO_THREADS. Must be a natural number")
+        }
     }
 }