Fix npm error when spawned in Windows

Issue rustwasm#277 - Affects running login, pack, and publish on Windows.

`Command::new("npm")` launched `npm` with quotes, `"npm"`, causing a
run-time error on Windows. Now, `Command::new` is wrapped by
`child::new_command(program: &str)`. This prepends `cmd /c` to the
program name if `cfg!(windows)`.

See rustc: #42436, #42791, #44542

src/child.rs

@@ -7,7 +7,9 @@ use failure::Error;
 use slog::Logger;
 use std::{
     io::{self, Read},
-    mem, process, string,
+    mem,
+    process::{Command, Stdio},
+    string,
     sync::mpsc,
     thread,
 };
@@ -19,6 +21,22 @@ enum OutputFragment {
     Stderr(Vec<u8>),
 }
 
+/// Return a new Command object
+pub fn new_command(program: &str) -> Command {
+    // On Windows, initializes launching <program> as `cmd /c <program>`.
+    // Initializing only with `Command::new("npm")` will launch
+    //   `npm` with quotes, `"npm"`, causing a run-time error on Windows.
+    // See rustc: #42436, #42791, #44542
+
+    if cfg!(windows) {
+        let mut cmd = Command::new("cmd");
+        cmd.arg("/c").arg(program);
+        cmd
+    } else {
+        Command::new(program)
+    }
+}
+
 /// Read data from the give reader and send it as an `OutputFragment` over the
 /// given sender.
 fn read_and_send<R, F>(
@@ -115,16 +133,12 @@ where
 }
 
 /// Run the given command and return its stdout.
-pub fn run(
-    logger: &Logger,
-    mut command: process::Command,
-    command_name: &str,
-) -> Result<String, Error> {
+pub fn run(logger: &Logger, mut command: Command, command_name: &str) -> Result<String, Error> {
     info!(logger, "Running {:?}", command);
 
     let mut child = command
-        .stdout(process::Stdio::piped())
-        .stderr(process::Stdio::piped())
+        .stdout(Stdio::piped())
+        .stderr(Stdio::piped())
         .spawn()?;
 
     let stdout = child.stdout.take().unwrap();

src/npm.rs

@@ -4,22 +4,21 @@ use child;
 use command::publish::access::Access;
 use failure::{self, ResultExt};
 use slog::Logger;
-use std::process::Command;
 
 /// The default npm registry used when we aren't working with a custom registry.
 pub const DEFAULT_NPM_REGISTRY: &'static str = "https://registry.npmjs.org/";
 
 /// Run the `npm pack` command.
 pub fn npm_pack(log: &Logger, path: &str) -> Result<(), failure::Error> {
-    let mut cmd = Command::new("npm");
+    let mut cmd = child::new_command("npm");
     cmd.current_dir(path).arg("pack");
     child::run(log, cmd, "npm pack").context("Packaging up your code failed")?;
     Ok(())
 }
 
 /// Run the `npm publish` command.
 pub fn npm_publish(log: &Logger, path: &str, access: Option<Access>) -> Result<(), failure::Error> {
-    let mut cmd = Command::new("npm");
+    let mut cmd = child::new_command("npm");
     match access {
         Some(a) => cmd
             .current_dir(path)
@@ -56,7 +55,7 @@ pub fn npm_login(
 
     // Interactively ask user for npm login info.
     //  (child::run does not support interactive input)
-    let mut cmd = Command::new("npm");
+    let mut cmd = child::new_command("npm");
     cmd.args(args);
 
     info!(log, "Running {:?}", cmd);