feat(tvix/eval): implement list concatenation r/4479

Change-Id: Icdf715d116371a9f139bdf95266410bf967bef25
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6144
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

7 files changed, 30 insertions, 0 deletions

diff --git a/tvix/eval/src/compiler.rs b/tvix/eval/src/compiler.rs
index 6054bd3fda..91eb1bda12 100644
--- a/tvix/eval/src/compiler.rs
+++ b/tvix/eval/src/compiler.rs
@@ -141,6 +141,7 @@ impl Compiler {
             BinOpKind::LessOrEq => self.chunk.add_op(OpCode::OpLessOrEq),
             BinOpKind::More => self.chunk.add_op(OpCode::OpMore),
             BinOpKind::MoreOrEq => self.chunk.add_op(OpCode::OpMoreOrEq),
+            BinOpKind::Concat => self.chunk.add_op(OpCode::OpConcat),
 
             BinOpKind::NotEqual => {
                 self.chunk.add_op(OpCode::OpEqual);
diff --git a/tvix/eval/src/opcode.rs b/tvix/eval/src/opcode.rs
index 6800e8411f..b1e6d32593 100644
--- a/tvix/eval/src/opcode.rs
+++ b/tvix/eval/src/opcode.rs
@@ -41,6 +41,7 @@ pub enum OpCode {
 
     // Lists
     OpList(usize),
+    OpConcat,
 
     // Strings
     OpInterpolate(usize),
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-concat-lists.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-concat-lists.exp
new file mode 100644
index 0000000000..3bed31f76e
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-concat-lists.exp
@@ -0,0 +1 @@
+[ 1 2 3 4 ]
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-concat-lists.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-concat-lists.nix
new file mode 100644
index 0000000000..de332cd29f
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-concat-lists.nix
@@ -0,0 +1 @@
+[ 1 2 ] ++ [ 3 4 ]
diff --git a/tvix/eval/src/value/list.rs b/tvix/eval/src/value/list.rs
index d5f7c8b2ba..f9d8522941 100644
--- a/tvix/eval/src/value/list.rs
+++ b/tvix/eval/src/value/list.rs
@@ -18,3 +18,12 @@ impl Display for NixList {
         f.write_str("]")
     }
 }
+
+impl NixList {
+    pub fn concat(&self, other: &Self) -> Self {
+        let mut lhs = self.clone();
+        let mut rhs = other.clone();
+        lhs.0.append(&mut rhs.0);
+        lhs
+    }
+}
diff --git a/tvix/eval/src/value/mod.rs b/tvix/eval/src/value/mod.rs
index 2a89f1c358..0c9042dbfe 100644
--- a/tvix/eval/src/value/mod.rs
+++ b/tvix/eval/src/value/mod.rs
@@ -81,6 +81,16 @@ impl Value {
             }),
         }
     }
+
+    pub fn as_list(self) -> EvalResult<NixList> {
+        match self {
+            Value::List(l) => Ok(l),
+            other => Err(Error::TypeError {
+                expected: "list",
+                actual: other.type_of(),
+            }),
+        }
+    }
 }
 
 impl Display for Value {
diff --git a/tvix/eval/src/vm.rs b/tvix/eval/src/vm.rs
index 30f2c5a4a4..540845d2c6 100644
--- a/tvix/eval/src/vm.rs
+++ b/tvix/eval/src/vm.rs
@@ -151,6 +151,13 @@ impl VM {
                 }
 
                 OpCode::OpList(count) => self.run_list(count)?,
+
+                OpCode::OpConcat => {
+                    let rhs = self.pop().as_list()?;
+                    let lhs = self.pop().as_list()?;
+                    self.push(Value::List(lhs.concat(&rhs)))
+                }
+
                 OpCode::OpInterpolate(count) => self.run_interpolate(count)?,
             }