om ci: Add devour-flake output path in result JSON (#359)

Useful to `nix copy` stuff back transitively
(#358 (comment)).


![image](https://github.com/user-attachments/assets/d920e413-8911-4f55-abe2-bbf0c7d59056)

crates/omnix-ci/src/command/run.rs

@@ -33,6 +33,8 @@ pub struct RunCommand {
     /// Must be a flake reference which, when imported, must return a Nix list
     /// of systems. You may use one of the lists from
     /// <https://github.com/nix-systems>.
+    ///
+    /// You can also pass the individual system name, if they are supported by omnix.
     #[arg(long)]
     pub systems: Option<SystemsListFlakeRef>,
 

crates/omnix-ci/src/nix/devour_flake.rs

@@ -5,7 +5,13 @@
 use anyhow::{bail, Context, Result};
 use nix_rs::{command::NixCmd, flake::url::FlakeUrl, store::path::StorePath};
 use serde::{Deserialize, Serialize};
-use std::{collections::HashMap, process::Stdio};
+use std::{
+    collections::HashMap,
+    ffi::OsString,
+    os::unix::ffi::OsStringExt,
+    path::{Path, PathBuf},
+    process::Stdio,
+};
 use tokio::io::{AsyncBufReadExt, BufReader};
 
 /// Absolute path to the devour-flake flake source
@@ -29,13 +35,19 @@ pub struct DevourFlakeOutput {
     /// Output paths indexed by name (or pname) of the path if any
     #[serde(rename = "byName")]
     pub by_name: HashMap<String, StorePath>,
+
+    /// The devour-flake output store path from which Self is derived.
+    #[serde(skip_deserializing, rename = "devourOutput")]
+    pub devour_output: PathBuf,
 }
 
 impl DevourFlakeOutput {
-    fn from_drv(drv_out: &str) -> anyhow::Result<Self> {
+    fn from_drv(drv_out: &Path) -> anyhow::Result<Self> {
         // Read drv_out file as JSON, decoding it into DevourFlakeOutput
         let mut out: DevourFlakeOutput = serde_json::from_reader(std::fs::File::open(drv_out)?)
             .context("Failed to parse devour-flake output")?;
+        // Provide the original devour-output store path itself.
+        out.devour_output = drv_out.to_owned();
         // Remove duplicates, which is possible in user's flake
         // e.g., when doing `packages.foo = self'.packages.default`
         out.out_paths.sort();
@@ -96,8 +108,8 @@ pub async fn devour_flake(
         .await
         .context("Unable to spawn devour-flake process")?;
     if output.status.success() {
-        let drv_out = String::from_utf8(output.stdout)?;
-        let v = DevourFlakeOutput::from_drv(drv_out.trim())?;
+        let drv_out = PathBuf::from(OsString::from_vec(output.stdout.trim_ascii_end().into()));
+        let v = DevourFlakeOutput::from_drv(&drv_out)?;
         Ok(v)
     } else {
         let exit_code = output.status.code().unwrap_or(1);