Don't always capture stdout, selectively do it

Add a separate function for running a child and capturing stdout

src/bindgen.rs

@@ -231,7 +231,7 @@ pub fn wasm_bindgen_build(
 fn wasm_bindgen_version_check(bindgen_path: &PathBuf, dep_version: &str) -> bool {
     let mut cmd = Command::new(bindgen_path);
     cmd.arg("--version");
-    child::run(cmd, "wasm-bindgen")
+    child::run_capture_stdout(cmd, "wasm-bindgen")
         .map(|stdout| {
             stdout
                 .trim()

src/build.rs

@@ -52,7 +52,8 @@ fn rustc_minor_version() -> Option<u32> {
 pub fn rustup_add_wasm_target(step: &Step) -> Result<(), Error> {
     let mut cmd = Command::new("rustc");
     cmd.arg("--print").arg("sysroot");
-    let output = child::run(cmd, "rustc").context("Learning about rustc's sysroot")?;
+    let output =
+        child::run_capture_stdout(cmd, "rustc").context("Learning about rustc's sysroot")?;
     let sysroot = Path::new(output.trim());
 
     // If this exists then we for sure have a wasm32 target so there's no need

src/child.rs

@@ -24,7 +24,24 @@ pub fn new_command(program: &str) -> Command {
 }
 
 /// Run the given command and return its stdout.
-pub fn run(mut command: Command, command_name: &str) -> Result<String, Error> {
+pub fn run(mut command: Command, command_name: &str) -> Result<(), Error> {
+    info!("Running {:?}", command);
+
+    let status = command.status()?;
+
+    if status.success() {
+        Ok(())
+    } else {
+        bail!(
+            "failed to execute `{}`: exited with {}",
+            command_name,
+            status
+        )
+    }
+}
+
+/// Run the given command and return its stdout.
+pub fn run_capture_stdout(mut command: Command, command_name: &str) -> Result<String, Error> {
     info!("Running {:?}", command);
 
     let output = command

tests/all/test.rs

@@ -331,9 +331,9 @@ fn test_output_is_printed_once_in_both_stdout_and_failures() {
         .arg("--node")
         .assert()
         .failure()
-        .stderr(predicate::function(|err: &str| {
-            // but the err string will capture both stdout and failures,
+        .stdout(predicate::function(|out: &str| {
+            // but the out string will capture both stdout and failures,
             // so we will get a log that count twice
-            err.matches("YABBA DABBA DOO").count() == log_cnt * 2
+            out.matches("YABBA DABBA DOO").count() == log_cnt * 2
         }));
 }