feat(tvix/eval): implement `builtins.path` r/7840

Now, it supports almost everything except `recursive = false;`, i.e. `flat`-ingestion
because we have no knob exposed in the tvix store import side to do it.

This has been tested to work.

Change-Id: I2e9da10ceccdfbf45b43c532077ed45d6306aa98
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10597
Tested-by: BuildkiteCI
Autosubmit: raitobezarius <tvl@lahfa.xyz>
Reviewed-by: flokli <flokli@flokli.de>

4 files changed, 335 insertions, 2 deletions

diff --git a/tvix/glue/src/builtins/errors.rs b/tvix/glue/src/builtins/errors.rs
index c753a125e030..53351cf902e7 100644
--- a/tvix/glue/src/builtins/errors.rs
+++ b/tvix/glue/src/builtins/errors.rs
@@ -53,3 +53,19 @@ impl From<FetcherError> for tvix_eval::ErrorKind {
         tvix_eval::ErrorKind::TvixError(Rc::new(err))
     }
 }
+
+/// Errors related to `builtins.path` and `builtins.filterSource`,
+/// a.k.a. "importing" builtins.
+#[derive(Debug, Error)]
+pub enum ImportError {
+    #[error("non-file '{0}' cannot be imported in 'flat' mode")]
+    FlatImportOfNonFile(String),
+    #[error("hash mismatch at ingestion of '{0}', expected: '{1}', got: '{2}'")]
+    HashMismatch(String, NixHash, NixHash),
+}
+
+impl From<ImportError> for tvix_eval::ErrorKind {
+    fn from(err: ImportError) -> Self {
+        tvix_eval::ErrorKind::TvixError(Rc::new(err))
+    }
+}
diff --git a/tvix/glue/src/builtins/import.rs b/tvix/glue/src/builtins/import.rs
index 8c9efc679171..fd791b8091fd 100644
--- a/tvix/glue/src/builtins/import.rs
+++ b/tvix/glue/src/builtins/import.rs
@@ -1,11 +1,12 @@
 //! Implements builtins used to import paths in the store.
 
+use crate::builtins::errors::ImportError;
 use futures::pin_mut;
 use std::path::Path;
 use tvix_eval::{
     builtin_macros::builtins,
     generators::{self, GenCo},
-    ErrorKind, Value,
+    ErrorKind, EvalIO, Value,
 };
 
 use std::rc::Rc;
@@ -123,8 +124,127 @@ mod import_builtins {
     use tvix_eval::generators::Gen;
     use tvix_eval::{generators::GenCo, ErrorKind, Value};
 
+    use tvix_castore::B3Digest;
+
     use crate::tvix_store_io::TvixStoreIO;
 
+    #[builtin("path")]
+    async fn builtin_path(
+        state: Rc<TvixStoreIO>,
+        co: GenCo,
+        args: Value,
+    ) -> Result<Value, ErrorKind> {
+        let args = args.to_attrs()?;
+        let path = args.select_required("path")?;
+        let path = generators::request_force(&co, path.clone())
+            .await
+            .to_path()?;
+        let name: String = if let Some(name) = args.select("name") {
+            generators::request_force(&co, name.clone())
+                .await
+                .to_str()?
+                .as_bstr()
+                .to_string()
+        } else {
+            tvix_store::import::path_to_name(&path)
+                .expect("Failed to derive the default name out of the path")
+                .to_string()
+        };
+        let filter = args.select("filter");
+        let recursive_ingestion = args
+            .select("recursive")
+            .map(|r| r.as_bool())
+            .transpose()?
+            .unwrap_or(true); // Yes, yes, Nix, by default, puts `recursive = true;`.
+        let expected_sha256 = args
+            .select("sha256")
+            .map(|h| {
+                h.to_str().and_then(|expected| {
+                    let expected = expected.into_bstring().to_string();
+                    // TODO: ensure that we fail if this is not a valid str.
+                    nix_compat::nixhash::from_str(&expected, None).map_err(|_err| {
+                        // TODO: a better error would be nice, we use
+                        // DerivationError::InvalidOutputHash usually for derivation construction.
+                        // This is not a derivation construction, should we move it outside and
+                        // generalize?
+                        ErrorKind::TypeError {
+                            expected: "sha256",
+                            actual: "not a sha256",
+                        }
+                    })
+                })
+            })
+            .transpose()?;
+
+        // FUTUREWORK(performance): this reads the file instead of using a stat-like
+        // system call to the file, this degrades very badly on large files.
+        if !recursive_ingestion && state.read_to_end(path.as_ref()).is_err() {
+            Err(ImportError::FlatImportOfNonFile(
+                path.to_string_lossy().to_string(),
+            ))?;
+        }
+
+        let root_node = filtered_ingest(state.clone(), co, path.as_ref(), filter).await?;
+        let ca: CAHash = if recursive_ingestion {
+            CAHash::Nar(NixHash::Sha256(state.tokio_handle.block_on(async {
+                Ok::<_, tvix_eval::ErrorKind>(
+                    state
+                        .path_info_service
+                        .as_ref()
+                        .calculate_nar(&root_node)
+                        .await
+                        .map_err(|e| ErrorKind::TvixError(Rc::new(e)))?
+                        .1,
+                )
+            })?))
+        } else {
+            let digest: B3Digest = match root_node {
+                tvix_castore::proto::node::Node::File(ref fnode) => {
+                    // It's already validated.
+                    fnode.digest.clone().try_into().unwrap()
+                }
+                // We cannot hash anything else than file in flat import mode.
+                _ => {
+                    return Err(ImportError::FlatImportOfNonFile(
+                        path.to_string_lossy().to_string(),
+                    )
+                    .into())
+                }
+            };
+
+            // FUTUREWORK: avoid hashing again.
+            CAHash::Flat(NixHash::Sha256(
+                state
+                    .tokio_handle
+                    .block_on(async { state.blob_to_sha256_hash(digest).await })?,
+            ))
+        };
+
+        let obtained_hash = ca.hash().clone().into_owned();
+        let (path_info, output_path) = state.tokio_handle.block_on(async {
+            state
+                .node_to_path_info(name.as_ref(), path.as_ref(), ca, root_node)
+                .await
+        })?;
+
+        if let Some(expected_sha256) = expected_sha256 {
+            if obtained_hash != expected_sha256 {
+                Err(ImportError::HashMismatch(
+                    path.to_string_lossy().to_string(),
+                    expected_sha256,
+                    obtained_hash,
+                ))?;
+            }
+        }
+
+        let _: tvix_store::proto::PathInfo = state.tokio_handle.block_on(async {
+            // This is necessary to cause the coercion of the error type.
+            Ok::<_, std::io::Error>(state.path_info_service.as_ref().put(path_info).await?)
+        })?;
+
+        Ok(output_path.to_absolute_path().into())
+    }
+
     #[builtin("filterSource")]
     async fn builtin_filter_source(
         state: Rc<TvixStoreIO>,
diff --git a/tvix/glue/src/builtins/mod.rs b/tvix/glue/src/builtins/mod.rs
index 138a52633da8..7cfe9f90a621 100644
--- a/tvix/glue/src/builtins/mod.rs
+++ b/tvix/glue/src/builtins/mod.rs
@@ -10,7 +10,7 @@ mod fetchers;
 mod import;
 mod utils;
 
-pub use errors::{DerivationError, FetcherError};
+pub use errors::{DerivationError, FetcherError, ImportError};
 
 /// Adds derivation-related builtins to the passed [tvix_eval::Evaluation].
 ///
@@ -438,6 +438,182 @@ mod tests {
         assert!(eval_result.errors.is_empty(), "errors should be empty");
     }
 
+    // Space is an illegal character.
+    #[test_case(
+        r#"(builtins.path { name = "valid-name"; path = @fixtures + "/te st"; recursive = true; })"#,
+        true
+    )]
+    // Space is still an illegal character.
+    #[test_case(
+        r#"(builtins.path { name = "invalid name"; path = @fixtures + "/te st"; recursive = true; })"#,
+        false
+    )]
+    fn builtins_path_recursive_rename(code: &str, success: bool) {
+        // populate the fixtures dir
+        let temp = TempDir::new().expect("create temporary directory");
+        let p = temp.path().join("import_fixtures");
+
+        // create the fixtures directory.
+        // We produce them at runtime rather than shipping it inside the source
+        // tree, as git can't model certain things - like directories without any
+        // items.
+        {
+            fs::create_dir(&p).expect("creating import_fixtures");
+            fs::write(p.join("te st"), "").expect("creating `/te st`");
+        }
+        // replace @fixtures with the temporary path containing the fixtures
+        let code_replaced = code.replace("@fixtures", &p.to_string_lossy());
+
+        let eval_result = eval(&code_replaced);
+
+        let value = eval_result.value;
+
+        if success {
+            match value.expect("expected successful evaluation on legal rename") {
+                tvix_eval::Value::String(s) => {
+                    assert_eq!(
+                        "/nix/store/nd5z11x7zjqqz44rkbhc6v7yifdkn659-valid-name",
+                        s.as_bstr()
+                    );
+                }
+                v => panic!("unexpected value type: {:?}", v),
+            }
+        } else {
+            assert!(value.is_none(), "unexpected success on illegal store paths");
+        }
+    }
+
+    // Space is an illegal character.
+    #[test_case(
+        r#"(builtins.path { name = "valid-name"; path = @fixtures + "/te st"; recursive = false; })"#,
+        true
+    )]
+    // Space is still an illegal character.
+    #[test_case(
+        r#"(builtins.path { name = "invalid name"; path = @fixtures + "/te st"; recursive = false; })"#,
+        false
+    )]
+    // The non-recursive variant passes explicitly `recursive = false;`
+    fn builtins_path_nonrecursive_rename(code: &str, success: bool) {
+        // populate the fixtures dir
+        let temp = TempDir::new().expect("create temporary directory");
+        let p = temp.path().join("import_fixtures");
+
+        // create the fixtures directory.
+        // We produce them at runtime rather than shipping it inside the source
+        // tree, as git can't model certain things - like directories without any
+        // items.
+        {
+            fs::create_dir(&p).expect("creating import_fixtures");
+            fs::write(p.join("te st"), "").expect("creating `/te st`");
+        }
+        // replace @fixtures with the temporary path containing the fixtures
+        let code_replaced = code.replace("@fixtures", &p.to_string_lossy());
+
+        let eval_result = eval(&code_replaced);
+
+        let value = eval_result.value;
+
+        if success {
+            match value.expect("expected successful evaluation on legal rename") {
+                tvix_eval::Value::String(s) => {
+                    assert_eq!(
+                        "/nix/store/il2rmfbqgs37rshr8w7x64hd4d3b4bsa-valid-name",
+                        s.as_bstr()
+                    );
+                }
+                v => panic!("unexpected value type: {:?}", v),
+            }
+        } else {
+            assert!(value.is_none(), "unexpected success on illegal store paths");
+        }
+    }
+
+    #[test_case(
+        r#"(builtins.path { name = "valid-name"; path = @fixtures + "/te st"; recursive = false; sha256 = "sha256-47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU="; })"#,
+        true
+    )]
+    #[test_case(
+        r#"(builtins.path { name = "valid-name"; path = @fixtures + "/te st"; recursive = true; sha256 = "sha256-47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU="; })"#,
+        false
+    )]
+    #[test_case(
+        r#"(builtins.path { name = "valid-name"; path = @fixtures + "/te st"; recursive = true; sha256 = "sha256-d6xi4mKdjkX2JFicDIv5niSzpyI0m/Hnm8GGAIU04kY="; })"#,
+        true
+    )]
+    #[test_case(
+        r#"(builtins.path { name = "valid-name"; path = @fixtures + "/te st"; recursive = false; sha256 = "sha256-d6xi4mKdjkX2JFicDIv5niSzpyI0m/Hnm8GGAIU04kY="; })"#,
+        false
+    )]
+    fn builtins_path_fod_locking(code: &str, success: bool) {
+        // populate the fixtures dir
+        let temp = TempDir::new().expect("create temporary directory");
+        let p = temp.path().join("import_fixtures");
+
+        // create the fixtures directory.
+        // We produce them at runtime rather than shipping it inside the source
+        // tree, as git can't model certain things - like directories without any
+        // items.
+        {
+            fs::create_dir(&p).expect("creating import_fixtures");
+            fs::write(p.join("te st"), "").expect("creating `/te st`");
+        }
+        // replace @fixtures with the temporary path containing the fixtures
+        let code_replaced = code.replace("@fixtures", &p.to_string_lossy());
+
+        let eval_result = eval(&code_replaced);
+
+        let value = eval_result.value;
+
+        if success {
+            assert!(
+                value.is_some(),
+                "expected successful evaluation on legal rename and valid FOD sha256"
+            );
+        } else {
+            assert!(value.is_none(), "unexpected success on invalid FOD sha256");
+        }
+    }
+
+    #[test_case(
+        r#"(builtins.path { name = "valid-path"; path = @fixtures + "/te st dir"; filter = _: _: true; })"#,
+        "/nix/store/i28jmi4fwym4fw3flkrkp2mdxx50pdy0-valid-path"
+    )]
+    #[test_case(
+        r#"(builtins.path { name = "valid-path"; path = @fixtures + "/te st dir"; filter = _: _: false; })"#,
+        "/nix/store/pwza2ij9gk1fmzhbjnynmfv2mq2sgcap-valid-path"
+    )]
+    fn builtins_path_filter(code: &str, expected_outpath: &str) {
+        // populate the fixtures dir
+        let temp = TempDir::new().expect("create temporary directory");
+        let p = temp.path().join("import_fixtures");
+
+        // create the fixtures directory.
+        // We produce them at runtime rather than shipping it inside the source
+        // tree, as git can't model certain things - like directories without any
+        // items.
+        {
+            fs::create_dir(&p).expect("creating import_fixtures");
+            fs::create_dir(p.join("te st dir")).expect("creating `/te st dir`");
+            fs::write(p.join("te st dir").join("test"), "").expect("creating `/te st dir/test`");
+        }
+        // replace @fixtures with the temporary path containing the fixtures
+        let code_replaced = code.replace("@fixtures", &p.to_string_lossy());
+
+        let eval_result = eval(&code_replaced);
+
+        let value = eval_result.value.expect("must succeed");
+
+        match value {
+            tvix_eval::Value::String(s) => {
+                assert_eq!(expected_outpath, s.as_bstr());
+            }
+            _ => panic!("unexpected value type: {:?}", value),
+        }
+
+        assert!(eval_result.errors.is_empty(), "errors should be empty");
+    }
+
     // All tests filter out some unsupported (not representable in castore) nodes, confirming
     // invalid, but filtered-out nodes don't prevent ingestion of a path.
     #[cfg(target_family = "unix")]
diff --git a/tvix/glue/src/tvix_store_io.rs b/tvix/glue/src/tvix_store_io.rs
index bfdab0846165..7b675bfc7d88 100644
--- a/tvix/glue/src/tvix_store_io.rs
+++ b/tvix/glue/src/tvix_store_io.rs
@@ -21,6 +21,7 @@ use tokio::io::AsyncReadExt;
 use tracing::{error, instrument, warn, Level};
 use tvix_build::buildservice::BuildService;
 use tvix_eval::{ErrorKind, EvalIO, FileType, StdIO};
+use tvix_store::utils::AsyncIoBridge;
 use walkdir::DirEntry;
 
 use tvix_castore::{
@@ -341,6 +342,26 @@ impl TvixStoreIO {
         Ok(output_path)
     }
 
+    /// Transforms a BLAKE-3 digest into a SHA256 digest
+    /// by re-hashing the whole file.
+    pub(crate) async fn blob_to_sha256_hash(&self, blob_digest: B3Digest) -> io::Result<[u8; 32]> {
+        let mut reader = self
+            .blob_service
+            .open_read(&blob_digest)
+            .await?
+            .ok_or_else(|| {
+                io::Error::new(
+                    io::ErrorKind::NotFound,
+                    format!("blob represented by digest: '{}' not found", blob_digest),
+                )
+            })?;
+        // It is fine to use `AsyncIoBridge` here because hashing is not actually I/O.
+        let mut hasher = AsyncIoBridge(Sha256::new());
+
+        tokio::io::copy(&mut reader, &mut hasher).await?;
+        Ok(hasher.0.finalize().into())
+    }
+
     pub async fn store_path_exists<'a>(&'a self, store_path: StorePathRef<'a>) -> io::Result<bool> {
         Ok(self
             .path_info_service