implement import & scopedImport (WIP, ResolvePath resolves to string)

fix-vm/src/primops/io.rs

@@ -1 +1,181 @@
+use std::path::PathBuf;
 
+use fix_builtins::PrimOpPhase;
+use fix_common::StringId;
+use fix_error::Error;
+use gc_arena::{Gc, Mutation};
+use hashbrown::HashSet;
+
+use crate::bytecode_reader::BytecodeReader;
+use crate::value::*;
+use crate::{Break, CallFrame, PendingLoad, PendingScope, Step, Vm, VmRuntimeCtx, VmRuntimeCtxExt};
+
+impl<'gc> Vm<'gc> {
+    pub(crate) fn primop_import(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        // stack: [path]
+        let path_val = self.force_and_retry::<StrictValue>(reader, mc)?;
+        let path_str = match ctx.get_string(path_val) {
+            Some(s) => s.to_owned(),
+            None => {
+                return self.finish_err(Error::eval_error(format!(
+                    "expected a path string, got {}",
+                    path_val.ty()
+                )));
+            }
+        };
+        let abs = match resolve_import_target(&path_str) {
+            Ok(p) => p,
+            Err(e) => return self.finish_err(e),
+        };
+
+        if let Some(&cached) = self.import_cache.get(&abs) {
+            return self.return_from_primop(cached, reader);
+        }
+
+        // Stash the resolved path on the stack as a string-id so the
+        // finalizer can use it as the cache key. The slot we pop here was
+        // freed by `force_and_retry`, so we simply push.
+        let path_sid = ctx.intern_string(abs.to_string_lossy());
+        self.push(Value::new_inline(path_sid));
+        self.call_stack.push(CallFrame {
+            pc: PrimOpPhase::ImportFinalize.ip() as usize,
+            thunk: None,
+            env: self.env,
+        });
+
+        self.pending_load = Some(PendingLoad {
+            path: abs,
+            scope: None,
+        });
+        Step::Break(Break::LoadFile)
+    }
+
+    pub(crate) fn primop_import_finalize(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+    ) -> Step {
+        // stack: [path_sid, return_value]
+        let val = self.pop();
+        #[allow(clippy::unwrap_used)]
+        let path_sid = self.pop().as_inline::<StringId>().unwrap();
+        // The cache key is keyed by the absolute path string we interned in
+        // `primop_import`. Resolve it back to the host PathBuf.
+        let path_str = ctx.resolve_string(path_sid).to_owned();
+        self.import_cache.insert(PathBuf::from(path_str), val);
+        self.push(val);
+        let Some(CallFrame {
+            pc: ret_pc,
+            thunk: _,
+            env,
+        }) = self.call_stack.pop()
+        else {
+            unreachable!()
+        };
+        reader.set_pc(ret_pc);
+        // FIXME:
+        // self.call_depth -= 1;
+        self.env = env;
+        Step::Continue(())
+    }
+
+    pub(crate) fn primop_scoped_import(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        // stack: [scope, path]
+        let (scope_attrs, path_val) =
+            self.force_and_retry::<(Gc<AttrSet>, StrictValue)>(reader, mc)?;
+        let path_str = match ctx.get_string(path_val) {
+            Some(s) => s.to_owned(),
+            None => {
+                return self.finish_err(Error::eval_error(format!(
+                    "expected a path string, got {}",
+                    path_val.ty()
+                )));
+            }
+        };
+        let abs = match resolve_import_target(&path_str) {
+            Ok(p) => p,
+            Err(e) => return self.finish_err(e),
+        };
+
+        let keys: HashSet<StringId> = scope_attrs.entries.iter().map(|&(k, _)| k).collect();
+        let slot_id = self.scope_slots.len() as u32;
+        self.scope_slots.push(Value::new_gc(scope_attrs));
+
+        self.call_stack.push(CallFrame {
+            pc: PrimOpPhase::ScopedImportFinalize.ip() as usize,
+            thunk: None,
+            env: self.env,
+        });
+
+        self.pending_load = Some(PendingLoad {
+            path: abs,
+            scope: Some(PendingScope { keys, slot_id }),
+        });
+        Step::Break(Break::LoadFile)
+    }
+
+    pub(crate) fn primop_scoped_import_finalize(
+        &mut self,
+        _ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        _mc: &Mutation<'gc>,
+    ) -> Step {
+        // stack: [return_value]
+        // We intentionally do NOT pop the slot from `scope_slots` so that
+        // closures or thunks created inside the imported file can still
+        // resolve their scope after `scopedImport` returns.
+        let val = self.pop();
+        self.return_from_primop(val, reader)
+    }
+
+    pub(crate) fn primop_path_exists(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        let path_val = self.force_and_retry::<StrictValue>(reader, mc)?;
+        let path = match ctx.get_string(path_val) {
+            Some(s) => s.to_owned(),
+            None => {
+                return self.finish_err(Error::eval_error(format!(
+                    "expected a path string, got {}",
+                    path_val.ty()
+                )));
+            }
+        };
+        let must_be_dir = path.ends_with('/') || path.ends_with("/.");
+        let p = std::path::Path::new(&path);
+        let exists = if must_be_dir {
+            std::fs::metadata(p).map(|m| m.is_dir()).unwrap_or(false)
+        } else {
+            std::fs::symlink_metadata(p).is_ok()
+        };
+        self.return_from_primop(Value::new_inline(exists), reader)
+    }
+}
+
+/// Convert the user-supplied path string into an absolute, dotted-segment
+/// resolved `PathBuf` and append `default.nix` if the target is a directory.
+fn resolve_import_target(path: &str) -> Result<PathBuf, Box<Error>> {
+    let mut abs = PathBuf::from(path);
+    if !abs.is_absolute() {
+        return Err(Error::eval_error(format!(
+            "import: expected an absolute path, got '{path}'"
+        )));
+    }
+    if abs.is_dir() {
+        abs.push("default.nix");
+    }
+    Ok(abs)
+}