compose: Initial kickstart support

The treefile syntax is...ok, but it is bespoke to us and
we never really emphasized its use outside of our sphere.

As I'm looking at https://gitlab.com/fedora/bootc/tracker/-/issues/32
I'd really like to expose something that has existing widespread
use as a default entrypoint.

kickstart is really old, long predating even virtualization.

It has a decent set of features (includes, comments) as a baseline
specifically as a mechanism to define package sets, it has key
features we want:

- turning off weak dependencies
- excludes

This is just a stub kickstart parser...the next step is to
wire this up into the treefile.

Signed-off-by: Colin Walters <walters@verbum.org>

Cargo.toml

@@ -92,6 +92,7 @@ tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 tokio = { version = "1.40.0", features = ["time", "process", "rt", "net"] }
 xmlrpc = "0.15.1"
 termcolor = "1.4.1"
+shlex = "1.3.0"
 
 [build-dependencies]
 anyhow = "1.0"

docs/treefile.md

@@ -526,6 +526,17 @@ version of `rpm-ostree`.
      and are purely machine-local state.
    - `root`: These are plain directories; only use this with composefs enabled!
 
+### Kickstarts
+
+A file ending in `.ks` will be parsed as a
+[kickstart file](https://pykickstart.readthedocs.io/en/latest/kickstart-docs.html).
+Only a small subset of kickstart configuration is honored:
+
+- `%packages` (both install and excludes via prefixing with `-`)
+  The only supported argument is `--exclude-weakdeps`, which translates
+  to `recommends: false`. Note that this has a global effect if set.
+- `%include` (Only child paths from the included file, not absolute paths)
+
 ### Associated directories
 
 In edition `2024`, "associated directories" have been introduced as an experimental feature. These

rust/src/kickstart.rs

@@ -0,0 +1,256 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+//! This is a Rust implementation of a small subset of the kickstart
+//! file format. It may grow in the future.
+
+use std::{
+    collections::HashSet,
+    io::{BufReader, Read},
+};
+
+use anyhow::{Context, Result};
+use cap_std::fs::{Dir, MetadataExt};
+use clap::Parser;
+
+// Cap includes just to avoid stack overflow in pathological cases
+const MAX_INCLUDES: usize = 256;
+const INCLUDE: &str = "%include";
+const PACKAGES: &str = "%packages";
+const END: &str = "%end";
+
+#[derive(clap::Parser, Debug)]
+pub(crate) struct PackageArgs {
+    /// Do not include weak dependencies
+    #[clap(long)]
+    pub(crate) exclude_weakdeps: bool,
+}
+
+#[derive(Debug)]
+pub(crate) struct Packages {
+    pub(crate) args: PackageArgs,
+    pub(crate) install: Vec<String>,
+    pub(crate) excludes: Vec<String>,
+}
+
+#[derive(Debug)]
+pub(crate) struct Kickstart {
+    pub(crate) includes: Vec<String>,
+    pub(crate) packages: Vec<Packages>,
+}
+
+#[derive(Debug)]
+pub(crate) struct KickstartParsed {
+    pub(crate) packages: Vec<Packages>,
+}
+
+fn filtermap_line(line: &str) -> Option<&str> {
+    // Ignore comments
+    if line.starts_with('#') {
+        return None;
+    }
+    let line = line.trim();
+    if line.is_empty() {
+        return None;
+    }
+    Some(line)
+}
+
+impl Packages {
+    fn parse<'a, 'b>(
+        args: impl Iterator<Item = &'b str>,
+        mut lines: impl Iterator<Item = &'a str>,
+    ) -> Result<Self> {
+        // Ensure there's an argv0
+        let args = [PACKAGES].into_iter().chain(args);
+        let args = PackageArgs::try_parse_from(args)?;
+        let mut install = Vec::new();
+        let mut excludes = Vec::new();
+        while let Some(line) = lines.next() {
+            let line = line.trim();
+            if line == END {
+                return Ok(Self {
+                    args,
+                    install,
+                    excludes,
+                });
+            }
+            if let Some(rest) = line.strip_prefix('-') {
+                excludes.push(rest.to_owned());
+            } else {
+                install.push(line.to_owned());
+            }
+        }
+        anyhow::bail!("Missing {END} for {PACKAGES}")
+    }
+}
+
+impl Kickstart {
+    pub(crate) fn parse(s: &str) -> Result<Self> {
+        let mut includes = Vec::new();
+        let mut packages = Vec::new();
+        let mut lines = s.lines().filter_map(filtermap_line);
+        while let Some(line) = lines.next() {
+            let line =
+                shlex::split(line).ok_or_else(|| anyhow::anyhow!("Invalid syntax: {line}"))?;
+            let mut line = line.iter();
+            let Some(verb) = line.next() else { continue };
+            let mut line = line.map(|s| s.as_str());
+            match verb.as_str() {
+                PACKAGES => {
+                    packages.push(Packages::parse(line, &mut lines)?);
+                }
+                INCLUDE => {
+                    let include = line
+                        .next()
+                        .ok_or_else(|| anyhow::anyhow!("Missing path for {INCLUDE}"))?;
+                    if line.next().is_some() {
+                        anyhow::bail!("Too many arguments for {INCLUDE}");
+                    }
+                    includes.push(include.to_owned());
+                }
+                o => {
+                    anyhow::bail!("Unhandled verb: {o}")
+                }
+            }
+        }
+        Ok(Self { includes, packages })
+    }
+}
+
+impl KickstartParsed {
+    pub(crate) fn new(d: &Dir, path: &str) -> Result<Self> {
+        let mut loaded = HashSet::new();
+        Self::new_recurse(d, path, &mut loaded)
+    }
+
+    pub(crate) fn new_recurse(
+        d: &Dir,
+        path: &str,
+        loaded: &mut HashSet<(u64, u64)>,
+    ) -> Result<Self> {
+        let mut ret = KickstartParsed {
+            packages: Vec::new(),
+        };
+        let f = d.open(path).with_context(|| format!("Opening {path}"))?;
+        let devino = f.metadata().map(|m| (m.dev(), m.ino()))?;
+        if !loaded.insert(devino) {
+            anyhow::bail!("Recursive include: {path}");
+        }
+        anyhow::ensure!(loaded.len() < MAX_INCLUDES);
+        let mut f = BufReader::new(f);
+        let mut s = String::new();
+        f.read_to_string(&mut s)?;
+        let ks = Kickstart::parse(&s)?;
+        ret.packages.extend(ks.packages);
+        for include in ks.includes {
+            let child = KickstartParsed::new_recurse(d, &include, loaded)?;
+            ret.packages.extend(child.packages);
+        }
+        Ok(ret)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use cap_std_ext::cap_tempfile::TempDir;
+
+    use super::*;
+
+    #[test]
+    fn test_filtermap_line() {
+        let nones = ["", "   ", "# foo"];
+        for v in nones.iter() {
+            assert_eq!(filtermap_line(v), None);
+        }
+        let idem = ["foo bar baz"];
+        for &v in idem.iter() {
+            assert_eq!(filtermap_line(v), Some(v));
+        }
+    }
+
+    #[test]
+    fn test_basic() {
+        let ks = Kickstart::parse(indoc::indoc! { r#"
+            # This is a comment
+            %include foo.ks
+            # Include this
+            %include subdir/bar.ks
+            # Blank line below
+
+            %packages
+            foo
+            -bar
+            baz
+            %end
+        "# })
+        .unwrap();
+        assert_eq!(ks.includes.len(), 2);
+        assert_eq!(ks.includes[1].as_str(), "subdir/bar.ks");
+        assert_eq!(ks.packages.len(), 1);
+        let pkgs = ks.packages.first().unwrap();
+        assert_eq!(pkgs.install.len(), 2);
+        assert_eq!(pkgs.excludes.len(), 1);
+    }
+
+    #[test]
+    fn test_load_from_dir() -> Result<()> {
+        let td = TempDir::new(cap_std::ambient_authority())?;
+        td.write("empty.ks", "")?;
+        let ks = KickstartParsed::new(&td, "empty.ks").unwrap();
+        assert_eq!(ks.packages.len(), 0);
+
+        td.create_dir("subdir")?;
+        td.write(
+            "subdir/inc.ks",
+            indoc::indoc! { r#"
+            %packages --exclude-weakdeps
+            systemd
+            # Let's go modern
+            -bash
+            nushell
+            %end
+        "#},
+        )?;
+
+        td.write(
+            "basic.ks",
+            indoc::indoc! { r#"
+            %packages
+            foo
+            -bar
+            baz
+            %end
+            # Our includes
+            %include empty.ks
+            %include subdir/inc.ks
+        "#},
+        )?;
+
+        let ks = KickstartParsed::new(&td, "basic.ks").unwrap();
+        assert_eq!(ks.packages.len(), 2);
+        let pkgs = &ks.packages[0];
+        assert!(!pkgs.args.exclude_weakdeps);
+        assert_eq!(pkgs.install[0], "foo");
+        assert!(ks.packages[1].args.exclude_weakdeps);
+        assert_eq!(ks.packages[1].excludes[0], "bash");
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_loop() -> Result<()> {
+        let td = TempDir::new(cap_std::ambient_authority())?;
+        td.write("recursive1.ks", "%include recursive2.ks")?;
+        td.write("recursive2.ks", "%include recursive1.ks")?;
+        assert!(KickstartParsed::new(&td, "recursive1.ks").is_err());
+        Ok(())
+    }
+
+    #[test]
+    fn test_parse_err() {
+        let errs = ["%packages\n", "%packages --foo\n%end\n"];
+        for err in errs {
+            assert!(Kickstart::parse(err).is_err());
+        }
+    }
+}

rust/src/lib.rs

@@ -990,6 +990,7 @@ pub(crate) use self::initramfs::*;
 mod isolation;
 mod journal;
 pub(crate) use self::journal::*;
+mod kickstart;
 mod lockfile;
 pub(crate) use self::lockfile::*;
 mod live;