refactor: give every command we run a type of its own

src/cmd/argv.rs

@@ -0,0 +1,206 @@
+use std::{
+    fmt::Display,
+    fs::File,
+    os::unix::process::CommandExt,
+    path::Path,
+    process::{Command, ExitStatus, Output, Stdio},
+};
+
+use anyhow::{Context, Result, anyhow};
+
+use crate::ctx::Ctx;
+
+// a program and its arguments: the only thing in ahab that knows what argv looks like
+#[derive(Default, Clone)]
+pub struct Argv(Vec<String>);
+
+impl Display for Argv {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str(&self.quoted())
+    }
+}
+
+impl Argv {
+    pub fn new(program: &str) -> Self {
+        Self(vec![program.to_string()])
+    }
+
+    pub fn arg(mut self, arg: impl AsRef<str>) -> Self {
+        self.0.push(arg.as_ref().to_string());
+        self
+    }
+
+    pub fn args<I, S>(mut self, args: I) -> Self
+    where
+        I: IntoIterator<Item = S>,
+        S: AsRef<str>,
+    {
+        self.0
+            .extend(args.into_iter().map(|arg| arg.as_ref().to_string()));
+        self
+    }
+
+    // a long option and the value it takes
+    pub fn flag(self, name: &str, value: impl AsRef<str>) -> Self {
+        self.arg(name).arg(value)
+    }
+
+    pub fn program(&self) -> &str {
+        self.0.first().map(String::as_str).unwrap_or_default()
+    }
+
+    pub fn words(&self) -> &[String] {
+        &self.0
+    }
+
+    // one word list for `sh -c`, quoted so a value with a space survives the shell
+    pub fn quoted(&self) -> String {
+        // a nul byte is the only thing shlex refuses, and no argv can hold one
+        shlex::try_join(self.0.iter().map(String::as_str)).unwrap_or_default()
+    }
+
+    pub fn run(&self, ctx: &Ctx) -> Result<()> {
+        if self.skipped(ctx) {
+            return Ok(());
+        }
+
+        let status = self.command(ctx)?.spawn()?.wait()?;
+
+        self.check(status)
+    }
+
+    // reading changes nothing, so a dry run answers the question for real
+    pub fn capture(&self, ctx: &Ctx) -> Result<String> {
+        let out = self.command(ctx)?.output()?;
+
+        if !out.status.success() {
+            // output() holds stderr back, so the command's own complaint has to be
+            // passed on here or it is lost
+            let stderr = String::from_utf8_lossy(&out.stderr);
+
+            return Err(match stderr.trim() {
+                "" => self.failure(out.status),
+                reason => anyhow!("`{self}` failed: {reason}"),
+            });
+        }
+
+        Ok(String::from_utf8(out.stdout)?)
+    }
+
+    // replaces this process, so the command's exit code and signals become ours
+    pub fn replace(&self, ctx: &Ctx) -> Result<()> {
+        if self.skipped(ctx) {
+            return Ok(());
+        }
+
+        let error = self.command(ctx)?.exec();
+
+        Err(error).with_context(|| format!("running `{self}`"))
+    }
+
+    pub fn stream_to(&self, ctx: &Ctx, out: Stdio) -> Result<()> {
+        if self.skipped(ctx) {
+            return Ok(());
+        }
+
+        let status = self.command(ctx)?.stdout(out).spawn()?.wait()?;
+
+        self.check(status)
+    }
+
+    // the status rather than an error, for callers with something better to say
+    pub fn status(&self, ctx: &Ctx) -> Result<ExitStatus> {
+        Ok(self.command(ctx)?.spawn()?.wait()?)
+    }
+
+    pub fn stdin_from(&self, ctx: &Ctx, input: &Path) -> Result<ExitStatus> {
+        let stdin = self.opened(input)?;
+
+        Ok(self.command(ctx)?.stdin(stdin).spawn()?.wait()?)
+    }
+
+    // both streams held back, for callers that read the command's complaints
+    pub fn stdin_from_captured(&self, ctx: &Ctx, input: &Path) -> Result<Output> {
+        let stdin = self.opened(input)?;
+
+        Ok(self.command(ctx)?.stdin(stdin).output()?)
+    }
+
+    // whether it succeeded, without failure being an error
+    pub fn quietly_succeeds(&self, ctx: &Ctx) -> Result<bool> {
+        Ok(self
+            .command(ctx)?
+            .stdout(Stdio::null())
+            .spawn()?
+            .wait()?
+            .success())
+    }
+
+    fn command(&self, ctx: &Ctx) -> Result<Command> {
+        if ctx.verbose {
+            eprintln!("running `{self}`");
+        }
+
+        let (program, rest) = self.0.split_first().context("empty command")?;
+        let mut command = Command::new(program);
+        command.args(rest);
+
+        Ok(command)
+    }
+
+    fn skipped(&self, ctx: &Ctx) -> bool {
+        if ctx.dry_run {
+            eprintln!("would run `{self}`");
+            return true;
+        }
+
+        false
+    }
+
+    fn opened(&self, path: &Path) -> Result<Stdio> {
+        let file = File::open(path).with_context(|| format!("opening {}", path.display()))?;
+
+        Ok(Stdio::from(file))
+    }
+
+    fn check(&self, status: ExitStatus) -> Result<()> {
+        if status.success() {
+            return Ok(());
+        }
+
+        Err(self.failure(status))
+    }
+
+    fn failure(&self, status: ExitStatus) -> anyhow::Error {
+        match status.code() {
+            Some(code) => anyhow!("`{self}` exited with {code}"),
+            None => anyhow!("`{self}` was killed by a signal"),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Argv;
+
+    #[test]
+    fn plain_words_are_left_as_they_are() {
+        let argv = Argv::new("pg_dump")
+            .flag("--username", "myproject")
+            .arg("--data-only")
+            .arg("myproject_db");
+
+        assert_eq!(
+            argv.quoted(),
+            "pg_dump --username myproject --data-only myproject_db"
+        );
+    }
+
+    #[test]
+    fn anything_a_shell_would_read_as_more_than_one_word_is_quoted() {
+        assert_eq!(Argv::new("psql").arg("my db").quoted(), "psql 'my db'");
+        assert_eq!(Argv::new("sh").arg("a | b").quoted(), "sh 'a | b'");
+        assert_eq!(Argv::new("echo").arg("").quoted(), "echo ''");
+        assert_eq!(Argv::new("echo").arg("it's").quoted(), r#"echo "it's""#);
+    }
+}