feat(nix/nint): accept attribute set with stdout, stderr and exit
This extends the calling convention for nint in a non-breaking way: If the called script returns an attribute set instead of a string the following is done: * If the attributes `stdout` and/or `stderr` exist, their content (which must be a string currently) is written to the respective output. * If the attribute `exit` exists, nint will exit with the given exit code. Must be a number that can be converted to an `i32`. If it's missing, nint will exit without indicating an error. Change-Id: I209cf178fee3d970fdea3b26e4049e944af47457 Reviewed-on: https://cl.tvl.fyi/c/depot/+/3547 Tested-by: BuildkiteCI Reviewed-by: tazjin <mail@tazj.in>
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2 changed files with 57 additions and 3 deletions
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@ -15,8 +15,16 @@ to the following calling convention:
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program name at `builtins.head argv`.
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* Extra arguments can be manually passed as described below.
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* The return value should always be a string (throwing is also okay)
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which is printed to stdout by `nint`.
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* The return value must either be
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* A string which is rendered to `stdout`.
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* An attribute set with the following optional attributes:
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* `stdout`: A string that's rendered to `stdout`
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* `stderr`: A string that's rendered to `stderr`
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* `exit`: A number which is used as an exit code.
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If missing, nint always exits with 0 (or equivalent).
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## Usage
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@ -5,6 +5,7 @@ use std::ffi::OsString;
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use std::os::unix::ffi::{OsStringExt, OsStrExt};
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use std::io::{Error, ErrorKind, Write, stdout, stderr};
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use std::process::Command;
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use std::convert::{TryFrom};
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fn render_nix_string(s: &OsString) -> OsString {
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let mut rendered = Vec::new();
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@ -40,6 +41,26 @@ fn render_nix_list(arr: &[OsString]) -> OsString {
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OsString::from_vec(rendered)
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}
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/// Slightly overkill helper macro which takes a `Map<String, Value>` obtained
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/// from `Value::Object` and an output name (`stderr` or `stdout`) as an
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/// identifier. If a value exists for the given output in the object it gets
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/// written to the appropriate output.
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macro_rules! handle_set_output {
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($map_name:ident, $output_name:ident) => {
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match $map_name.get(stringify!($output_name)) {
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Some(Value::String(s)) =>
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$output_name().write_all(s.as_bytes()),
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Some(_) => Err(
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Error::new(
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ErrorKind::Other,
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format!("Attribute {} must be a string!", stringify!($output_name)),
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)
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),
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None => Ok(()),
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}
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}
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}
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fn main() -> std::io::Result<()> {
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let mut nix_args = Vec::new();
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@ -90,6 +111,7 @@ fn main() -> std::io::Result<()> {
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nix_args.push(render_nix_list(&argv[..]));
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nix_args.push(OsString::from("--eval"));
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nix_args.push(OsString::from("--strict"));
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nix_args.push(OsString::from("--json"));
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nix_args.push(argv[0].clone());
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@ -100,7 +122,31 @@ fn main() -> std::io::Result<()> {
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match serde_json::from_slice(&run.stdout[..]) {
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Ok(Value::String(s)) => stdout().write_all(s.as_bytes()),
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Ok(_) => Err(Error::new(ErrorKind::Other, "output must be a string")),
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Ok(Value::Object(m)) => {
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handle_set_output!(m, stdout)?;
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handle_set_output!(m, stderr)?;
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match m.get("exit") {
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Some(Value::Number(n)) => {
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let code = n.as_i64().and_then(|v| i32::try_from(v).ok());
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match code {
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Some(i) => std::process::exit(i),
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None => Err(
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Error::new(
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ErrorKind::Other,
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"Attribute exit is not an i32"
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)
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),
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}
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},
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Some(_) => Err(
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Error::new(ErrorKind::Other, "exit must be a number")
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),
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None => Ok(()),
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}
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},
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Ok(_) => Err(Error::new(ErrorKind::Other, "output must be a string or an object")),
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_ => {
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stderr().write_all(&run.stderr[..]);
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Err(Error::new(ErrorKind::Other, "internal nix error"))
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