Make the output optional

src/cmd.rs

@@ -1,30 +1,42 @@
 use anyhow::{Context, Result};
-use std::{io::Read, path::Path, process::Command};
+use std::{
+    io::Read,
+    path::Path,
+    process::{Command, Stdio},
+};
 
 /// Run a command with a description for a possible error and append the merged stdout and stderr.
 /// The boolean in the returned `Result` is true if the command's exit status is success.
-pub fn run_cmd(mut cmd: Command, description: &str, output: &mut Vec<u8>) -> Result<bool> {
-    let (mut reader, writer) = os_pipe::pipe()
-        .with_context(|| format!("Failed to create a pipe to run the command `{description}``"))?;
+pub fn run_cmd(mut cmd: Command, description: &str, output: Option<&mut Vec<u8>>) -> Result<bool> {
+    let spawn = |mut cmd: Command| {
+        // NOTE: The closure drops `cmd` which prevents a pipe deadlock.
+        cmd.spawn()
+            .with_context(|| format!("Failed to run the command `{description}`"))
+    };
 
-    let writer_clone = writer.try_clone().with_context(|| {
-        format!("Failed to clone the pipe writer for the command `{description}`")
-    })?;
+    let mut handle = if let Some(output) = output {
+        let (mut reader, writer) = os_pipe::pipe().with_context(|| {
+            format!("Failed to create a pipe to run the command `{description}``")
+        })?;
 
-    let mut handle = cmd
-        .stdout(writer_clone)
-        .stderr(writer)
-        .spawn()
-        .with_context(|| format!("Failed to run the command `{description}`"))?;
+        let writer_clone = writer.try_clone().with_context(|| {
+            format!("Failed to clone the pipe writer for the command `{description}`")
+        })?;
 
-    // Prevent pipe deadlock.
-    drop(cmd);
+        cmd.stdout(writer_clone).stderr(writer);
+        let handle = spawn(cmd)?;
 
-    reader
-        .read_to_end(output)
-        .with_context(|| format!("Failed to read the output of the command `{description}`"))?;
+        reader
+            .read_to_end(output)
+            .with_context(|| format!("Failed to read the output of the command `{description}`"))?;
 
-    output.push(b'\n');
+        output.push(b'\n');
+
+        handle
+    } else {
+        cmd.stdout(Stdio::null()).stderr(Stdio::null());
+        spawn(cmd)?
+    };
 
     handle
         .wait()
@@ -42,14 +54,14 @@ pub struct CargoCmd<'a> {
     /// Added as `--target-dir` if `Self::dev` is true.
     pub target_dir: &'a Path,
     /// The output buffer to append the merged stdout and stderr.
-    pub output: &'a mut Vec<u8>,
+    pub output: Option<&'a mut Vec<u8>>,
     /// true while developing Rustlings.
     pub dev: bool,
 }
 
 impl<'a> CargoCmd<'a> {
     /// Run `cargo SUBCOMMAND --bin EXERCISE_NAME … ARGS`.
-    pub fn run(&mut self) -> Result<bool> {
+    pub fn run(self) -> Result<bool> {
         let mut cmd = Command::new("cargo");
         cmd.arg(self.subcommand);
 
@@ -86,7 +98,7 @@ mod tests {
         cmd.arg("Hello");
 
         let mut output = Vec::with_capacity(8);
-        run_cmd(cmd, "echo …", &mut output).unwrap();
+        run_cmd(cmd, "echo …", Some(&mut output)).unwrap();
 
         assert_eq!(output, b"Hello\n\n");
     }