feat(snix-glue): Correctly propagate output placeholders into the build.

Nix's `builtin.placeholder` function produces output paths that are not
known ahead of time, so before propagating these values into the build
we need to replace them in all env variables and arguments to their
corresponding output store paths.

fix #101

Change-Id: I2670c749f2c578e276d698e511598a76a99ebb96
Reviewed-on: https://cl.snix.dev/c/snix/+/30310
Tested-by: besadii
Reviewed-by: Florian Klink <flokli@flokli.de>
Autosubmit: Vova Kryachko <v.kryachko@gmail.com>

snix/glue/src/snix_build.rs

@@ -6,13 +6,17 @@ use std::future::Future;
 use std::path::PathBuf;
 
 use async_stream::try_stream;
+use bstr::BString;
 use bytes::Bytes;
 use futures::Stream;
+use nix_compat::derivation::Output;
+use nix_compat::store_path::hash_placeholder;
 use nix_compat::{derivation::Derivation, nixbase32, store_path::StorePath};
 use sha2::{Digest, Sha256};
 use snix_build::buildservice::{AdditionalFile, BuildConstraints, BuildRequest, EnvVar};
 use snix_castore::Node;
 use snix_store::path_info::PathInfo;
+use tracing::warn;
 
 use crate::known_paths::KnownPaths;
 
@@ -95,7 +99,14 @@ pub(crate) fn derivation_to_build_request(
     // produce command_args, which is builder and arguments in a Vec.
     let mut command_args: Vec<String> = Vec::with_capacity(derivation.arguments.len() + 1);
     command_args.push(derivation.builder.clone());
-    command_args.extend_from_slice(&derivation.arguments);
+    command_args.extend_from_slice(
+        derivation
+            .arguments
+            .iter()
+            .map(|arg| replace_placeholders(arg, &derivation.outputs))
+            .collect::<Vec<String>>()
+            .as_slice(),
+    );
 
     // Produce environment_vars and additional files.
     // We use a BTreeMap while producing, and only realize the resulting Vec
@@ -113,12 +124,12 @@ pub(crate) fn derivation_to_build_request(
     // extend / overwrite with the keys set in the derivation environment itself.
     // TODO: check if this order is correct, and environment vars set in the
     // *Derivation actually* have priority.
-    environment_vars.extend(
-        derivation
-            .environment
-            .iter()
-            .map(|(k, v)| (k.clone(), Bytes::from(v.to_vec()))),
-    );
+    environment_vars.extend(derivation.environment.iter().map(|(k, v)| {
+        (
+            k.clone(),
+            Bytes::from(replace_placeholders_b(v, &derivation.outputs).to_vec()),
+        )
+    }));
 
     handle_pass_as_file(&mut environment_vars, &mut additional_files)?;
 
@@ -247,9 +258,47 @@ fn calculate_pass_as_file_env(k: &str) -> (String, String) {
     )
 }
 
+/// Replace all references to `placeholder outputName` inside the derivation
+fn replace_placeholders(s: &str, outputs: &BTreeMap<String, Output>) -> String {
+    let mut s = s.to_owned();
+    for (out_name, output) in outputs {
+        let placeholder = hash_placeholder(out_name.as_str());
+        if let Some(path) = output.path.as_ref() {
+            s = s.replace(&placeholder, &path.to_absolute_path());
+        } else {
+            warn!(
+                output.name = out_name,
+                "output should have a path during placeholder replacement"
+            );
+        }
+    }
+    s
+}
+
+/// Replace all references to `placeholder outputName` inside the derivation
+fn replace_placeholders_b(s: &BString, outputs: &BTreeMap<String, Output>) -> BString {
+    use bstr::ByteSlice;
+    let mut s = s.clone();
+    for (out_name, output) in outputs {
+        let placeholder = hash_placeholder(out_name.as_str());
+        if let Some(path) = output.path.as_ref() {
+            s = s
+                .replace(placeholder.as_bytes(), path.to_absolute_path().as_bytes())
+                .into();
+        } else {
+            warn!(
+                output.name = out_name,
+                "output should have a path during placeholder replacement"
+            );
+        }
+    }
+    s
+}
+
 #[cfg(test)]
 mod test {
     use bytes::Bytes;
+    use nix_compat::store_path::hash_placeholder;
     use nix_compat::{derivation::Derivation, store_path::StorePath};
     use snix_castore::fixtures::DUMMY_DIGEST;
     use snix_castore::{Node, PathComponent};
@@ -356,6 +405,75 @@ mod test {
         );
     }
 
+    #[test]
+    fn test_drv_with_placeholders_to_build_request() {
+        let aterm_bytes =
+            include_bytes!("tests/18m7y1d025lqgrzx8ypnhjbvq23z2kda-with-placeholders.drv");
+        let derivation = Derivation::from_aterm_bytes(aterm_bytes).expect("must parse");
+
+        let build_request =
+            derivation_to_build_request(&derivation, &BTreeMap::from([])).expect("must succeed");
+        let mut expected_environment_vars = vec![
+            EnvVar {
+                key: "FOO".into(),
+                value: "/nix/store/dgapb8kh5gis4w7hzfl5725sx5gam0nz-with-placeholders".into(),
+            },
+            EnvVar {
+                key: "BAR".into(),
+                // Non existent output placeholders should not get replaced.
+                value: hash_placeholder("non-existent").into(),
+            },
+            EnvVar {
+                key: "builder".into(),
+                value: "/bin/sh".into(),
+            },
+            EnvVar {
+                key: "name".into(),
+                value: "with-placeholders".into(),
+            },
+            EnvVar {
+                key: "out".into(),
+                value: "/nix/store/dgapb8kh5gis4w7hzfl5725sx5gam0nz-with-placeholders".into(),
+            },
+            EnvVar {
+                key: "system".into(),
+                value: "x86_64-linux".into(),
+            },
+        ];
+        expected_environment_vars.extend(NIX_ENVIRONMENT_VARS.iter().map(|(k, v)| EnvVar {
+            key: k.to_string(),
+            value: Bytes::from_static(v.as_bytes()),
+        }));
+
+        expected_environment_vars.sort_unstable_by_key(|e| e.key.to_owned());
+        assert_eq!(
+            BuildRequest {
+                command_args: vec![
+                    "/bin/sh".into(),
+                    "-c".into(),
+                    "/nix/store/dgapb8kh5gis4w7hzfl5725sx5gam0nz-with-placeholders".into(),
+                    // Non existent output placeholders should not get replaced.
+                    hash_placeholder("non-existent"),
+                ],
+                outputs: vec![
+                    "nix/store/dgapb8kh5gis4w7hzfl5725sx5gam0nz-with-placeholders".into()
+                ],
+                environment_vars: expected_environment_vars,
+                inputs: BTreeMap::new(),
+                inputs_dir: "nix/store".into(),
+                constraints: HashSet::from([
+                    BuildConstraints::System(derivation.system.clone()),
+                    BuildConstraints::ProvideBinSh
+                ]),
+                additional_files: vec![],
+                working_dir: "build".into(),
+                scratch_paths: vec!["build".into(), "nix/store".into()],
+                refscan_needles: vec!["dgapb8kh5gis4w7hzfl5725sx5gam0nz".into()],
+            },
+            build_request
+        );
+    }
+
     #[test]
     fn test_fod_to_build_request() {
         let aterm_bytes = include_bytes!("tests/0hm2f1psjpcwg8fijsmr4wwxrx59s092-bar.drv");

snix/glue/src/tests/18m7y1d025lqgrzx8ypnhjbvq23z2kda-with-placeholders.drv

@@ -0,0 +1 @@
+Derive([("out","/nix/store/dgapb8kh5gis4w7hzfl5725sx5gam0nz-with-placeholders","","")],[],[],"x86_64-linux","/bin/sh",["-c","/1rz4g4znpzjwh1xymhjpm42vipw92pr73vdgl6xs1hycac8kf2n9","/1zwrijlc0ixcpdjslshwq3nd28rbbmp6812lh5c49ifrcc3gk3mz"],[("BAR","/1zwrijlc0ixcpdjslshwq3nd28rbbmp6812lh5c49ifrcc3gk3mz"),("FOO","/1rz4g4znpzjwh1xymhjpm42vipw92pr73vdgl6xs1hycac8kf2n9"),("builder","/bin/sh"),("name","with-placeholders"),("out","/nix/store/dgapb8kh5gis4w7hzfl5725sx5gam0nz-with-placeholders"),("system","x86_64-linux")])