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-rw-r--r--tvix/eval/src/compiler/mod.rs24
-rw-r--r--tvix/eval/src/opcode.rs2
-rw-r--r--tvix/eval/src/tests/tvix_tests/eval-okay-deeply-nested-with-closure.exp1
-rw-r--r--tvix/eval/src/tests/tvix_tests/eval-okay-deeply-nested-with-closure.nix18
-rw-r--r--tvix/eval/src/value/mod.rs8
-rw-r--r--tvix/eval/src/vm.rs71
6 files changed, 112 insertions, 12 deletions
diff --git a/tvix/eval/src/compiler/mod.rs b/tvix/eval/src/compiler/mod.rs
index 11d6d8231f09..78fe76ca01a9 100644
--- a/tvix/eval/src/compiler/mod.rs
+++ b/tvix/eval/src/compiler/mod.rs
@@ -702,6 +702,15 @@ impl Compiler {
                 if let Some(idx) =
                     self.resolve_dynamic_upvalue(self.contexts.len() - 1, ident.text())
                 {
+                    // Edge case: Current scope *also* has a non-empty
+                    // `with`-stack. This means we need to resolve
+                    // both in this scope, and in the upvalues.
+                    if self.scope().has_with() {
+                        self.emit_constant(Value::String(ident.text().into()));
+                        self.chunk().push_op(OpCode::OpResolveWithOrUpvalue(idx));
+                        return;
+                    }
+
                     self.chunk().push_op(OpCode::OpGetUpvalue(idx));
                     return;
                 }
@@ -810,11 +819,18 @@ impl Compiler {
         self.chunk().push_op(OpCode::OpClosure(closure_idx));
         for upvalue in compiled.scope.upvalues {
             match upvalue {
-                Upvalue::Stack(idx) => self.chunk().push_op(OpCode::DataLocalIdx(idx)),
-                Upvalue::Upvalue(idx) => self.chunk().push_op(OpCode::DataUpvalueIdx(idx)),
-                Upvalue::Dynamic { name, .. } => {
+                Upvalue::Stack(idx) => {
+                    self.chunk().push_op(OpCode::DataLocalIdx(idx));
+                }
+                Upvalue::Upvalue(idx) => {
+                    self.chunk().push_op(OpCode::DataUpvalueIdx(idx));
+                }
+                Upvalue::Dynamic { name, up } => {
                     let idx = self.chunk().push_constant(Value::String(name.into()));
-                    self.chunk().push_op(OpCode::DataDynamicIdx(idx))
+                    self.chunk().push_op(OpCode::DataDynamicIdx(idx));
+                    if let Some(up) = up {
+                        self.chunk().push_op(OpCode::DataDynamicAncestor(up));
+                    }
                 }
             };
         }
diff --git a/tvix/eval/src/opcode.rs b/tvix/eval/src/opcode.rs
index edf7a8a5dc4a..5f1f33f2b3e5 100644
--- a/tvix/eval/src/opcode.rs
+++ b/tvix/eval/src/opcode.rs
@@ -82,6 +82,7 @@ pub enum OpCode {
     OpPushWith(StackIdx),
     OpPopWith,
     OpResolveWith,
+    OpResolveWithOrUpvalue(UpvalueIdx),
 
     // Lists
     OpList(Count),
@@ -116,4 +117,5 @@ pub enum OpCode {
     DataLocalIdx(StackIdx),
     DataUpvalueIdx(UpvalueIdx),
     DataDynamicIdx(ConstantIdx),
+    DataDynamicAncestor(UpvalueIdx),
 }
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-deeply-nested-with-closure.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-deeply-nested-with-closure.exp
new file mode 100644
index 000000000000..3bed31f76e3f
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-deeply-nested-with-closure.exp
@@ -0,0 +1 @@
+[ 1 2 3 4 ]
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-deeply-nested-with-closure.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-deeply-nested-with-closure.nix
new file mode 100644
index 000000000000..7f13f1f27030
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-deeply-nested-with-closure.nix
@@ -0,0 +1,18 @@
+# This convoluted test constructs a situation in which dynamically
+# resolved upvalues refer `with` blocks introduced at different lambda
+# context boundaries, i.e. the access to a, b in the innermost closure
+# must be threaded through upvalues in several levels.
+
+(_:
+with { a = 1; b = 1; };
+
+_:
+with { b = 2; c = 2; };
+
+_:
+with { c = 3; d = 3; };
+
+_:
+with { d = 4; };
+
+[ a b c d ]) null null null null
diff --git a/tvix/eval/src/value/mod.rs b/tvix/eval/src/value/mod.rs
index eb23605bd0b2..54211e8ba313 100644
--- a/tvix/eval/src/value/mod.rs
+++ b/tvix/eval/src/value/mod.rs
@@ -34,6 +34,7 @@ pub enum Value {
     // are never returned to or created directly by users.
     AttrPath(Vec<NixString>),
     AttrNotFound,
+    DynamicUpvalueMissing(NixString),
 }
 
 impl Value {
@@ -54,7 +55,9 @@ impl Value {
             Value::Closure(_) | Value::Builtin(_) => "lambda",
 
             // Internal types
-            Value::AttrPath(_) | Value::AttrNotFound => "internal",
+            Value::AttrPath(_) | Value::AttrNotFound | Value::DynamicUpvalueMissing(_) => {
+                "internal"
+            }
         }
     }
 
@@ -163,6 +166,9 @@ impl Display for Value {
             // internal types
             Value::AttrPath(path) => write!(f, "internal[attrpath({})]", path.len()),
             Value::AttrNotFound => f.write_str("internal[not found]"),
+            Value::DynamicUpvalueMissing(name) => {
+                write!(f, "internal[no_dyn_upvalue({name})]")
+            }
         }
     }
 }
diff --git a/tvix/eval/src/vm.rs b/tvix/eval/src/vm.rs
index 23d9c3555153..5d5cb57dbabf 100644
--- a/tvix/eval/src/vm.rs
+++ b/tvix/eval/src/vm.rs
@@ -5,8 +5,8 @@ use std::{cell::Ref, rc::Rc};
 
 use crate::{
     chunk::Chunk,
-    errors::{ErrorKind, EvalResult},
-    opcode::{Count, JumpOffset, OpCode, StackIdx},
+    errors::{Error, ErrorKind, EvalResult},
+    opcode::{ConstantIdx, Count, JumpOffset, OpCode, StackIdx},
     value::{Closure, Lambda, NixAttrs, NixList, Value},
 };
 
@@ -100,6 +100,10 @@ impl VM {
         op
     }
 
+    fn peek_op(&self) -> OpCode {
+        self.chunk().code[self.frame().ip]
+    }
+
     fn pop(&mut self) -> Value {
         self.stack.pop().expect("runtime stack empty")
     }
@@ -337,6 +341,25 @@ impl VM {
                     self.push(value)
                 }
 
+                OpCode::OpResolveWithOrUpvalue(idx) => {
+                    let ident = self.pop().to_string()?;
+                    match self.resolve_with(ident.as_str()) {
+                        // Variable found in local `with`-stack.
+                        Ok(value) => self.push(value),
+
+                        // Variable not found => check upvalues.
+                        Err(Error {
+                            kind: ErrorKind::UnknownDynamicVariable(_),
+                            ..
+                        }) => {
+                            let value = self.frame().closure.upvalue(idx).clone();
+                            self.push(value);
+                        }
+
+                        Err(err) => return Err(err),
+                    }
+                }
+
                 OpCode::OpAssert => {
                     if !self.pop().as_bool()? {
                         return Err(ErrorKind::AssertionFailed.into());
@@ -389,10 +412,8 @@ impl VM {
                             }
 
                             OpCode::DataDynamicIdx(ident_idx) => {
-                                let chunk = self.chunk();
-                                let ident = chunk.constant(ident_idx).as_str()?.to_string();
-                                drop(chunk); // some lifetime trickery due to cell::Ref
-                                closure.push_upvalue(self.resolve_with(&ident)?);
+                                let value = self.resolve_dynamic_upvalue(ident_idx)?;
+                                closure.push_upvalue(value);
                             }
 
                             _ => panic!("compiler error: missing closure operand"),
@@ -402,7 +423,10 @@ impl VM {
 
                 // Data-carrying operands should never be executed,
                 // that is a critical error in the VM.
-                OpCode::DataLocalIdx(_) | OpCode::DataUpvalueIdx(_) | OpCode::DataDynamicIdx(_) => {
+                OpCode::DataLocalIdx(_)
+                | OpCode::DataUpvalueIdx(_)
+                | OpCode::DataDynamicIdx(_)
+                | OpCode::DataDynamicAncestor(_) => {
                     panic!("VM bug: attempted to execute data-carrying operand")
                 }
             }
@@ -452,6 +476,39 @@ impl VM {
         Ok(())
     }
 
+    fn resolve_dynamic_upvalue(&mut self, ident_idx: ConstantIdx) -> EvalResult<Value> {
+        let chunk = self.chunk();
+        let ident = chunk.constant(ident_idx).as_str()?.to_string();
+        drop(chunk); // some lifetime trickery due to cell::Ref
+
+        // Peek at the current instruction (note: IP has already
+        // advanced!) to see if it is actually data indicating a
+        // "fallback upvalue" in case the dynamic could not be
+        // resolved at this level.
+        let up = match self.peek_op() {
+            OpCode::DataDynamicAncestor(idx) => {
+                // advance ip past this data
+                self.inc_ip();
+                Some(idx)
+            }
+            _ => None,
+        };
+
+        match self.resolve_with(&ident) {
+            Ok(v) => Ok(v),
+
+            Err(Error {
+                kind: ErrorKind::UnknownDynamicVariable(_),
+                ..
+            }) => match up {
+                Some(idx) => Ok(self.frame().closure.upvalue(idx).clone()),
+                None => Ok(Value::DynamicUpvalueMissing(ident.into())),
+            },
+
+            Err(err) => Err(err),
+        }
+    }
+
     /// Resolve a dynamic identifier through the with-stack at runtime.
     fn resolve_with(&self, ident: &str) -> EvalResult<Value> {
         for idx in self.with_stack.iter().rev() {
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