refactor(tvix/eval): handle forcing in Builtin::apply r/4918

Instead of arity, we pass a array reference to Builtin::new that
describes how many arguments there are and which of them need to be
forced, eliminating the need to force manually.

Note that this change doesn't fix some of the instances where the the
Builtin doesn't consider that the value could be a Thunk.

Change-Id: Iadb58bb79886c30dc6b09dcf0ffad8abf28036a1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6662
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

1 files changed, 46 insertions, 58 deletions

diff --git a/tvix/eval/src/builtins/mod.rs b/tvix/eval/src/builtins/mod.rs
index 527a8f8530..10ec6c89f9 100644
--- a/tvix/eval/src/builtins/mod.rs
+++ b/tvix/eval/src/builtins/mod.rs
@@ -50,19 +50,18 @@ pub fn coerce_value_to_path(v: &Value, vm: &mut VM) -> Result<PathBuf, ErrorKind
 /// WASM).
 fn pure_builtins() -> Vec<Builtin> {
     vec![
-        Builtin::new("add", 2, |mut args, _| {
+        Builtin::new("add", &[true, true], |mut args, _| {
             let b = args.pop().unwrap();
             let a = args.pop().unwrap();
             arithmetic_op!(a, b, +)
         }),
-        Builtin::new("abort", 1, |mut args, _| {
+        Builtin::new("abort", &[true], |mut args, _| {
             return Err(ErrorKind::Abort(
                 args.pop().unwrap().to_str()?.as_str().to_owned(),
             ));
         }),
-        Builtin::new("attrNames", 1, |args, vm| {
-            let value = args[0].force(vm)?;
-            let xs = value.to_attrs()?;
+        Builtin::new("attrNames", &[true], |args, _| {
+            let xs = args[0].to_attrs()?;
             let mut output = Vec::with_capacity(xs.len());
 
             for (key, _val) in xs.iter() {
@@ -71,9 +70,8 @@ fn pure_builtins() -> Vec<Builtin> {
 
             Ok(Value::List(NixList::construct(output.len(), output)))
         }),
-        Builtin::new("attrValues", 1, |args, vm| {
-            let value = args[0].force(vm)?;
-            let xs = value.to_attrs()?;
+        Builtin::new("attrValues", &[true], |args, _| {
+            let xs = args[0].to_attrs()?;
             let mut output = Vec::with_capacity(xs.len());
 
             for (_key, val) in xs.iter() {
@@ -82,22 +80,16 @@ fn pure_builtins() -> Vec<Builtin> {
 
             Ok(Value::List(NixList::construct(output.len(), output)))
         }),
-        Builtin::new("bitAnd", 2, |args, vm| {
-            let x = args[0].force(vm)?;
-            let y = args[1].force(vm)?;
-            Ok(Value::Integer(x.as_int()? & y.as_int()?))
+        Builtin::new("bitAnd", &[true, true], |args, _| {
+            Ok(Value::Integer(args[0].as_int()? & args[1].as_int()?))
         }),
-        Builtin::new("bitOr", 2, |args, vm| {
-            let x = args[0].force(vm)?;
-            let y = args[1].force(vm)?;
-            Ok(Value::Integer(x.as_int()? | y.as_int()?))
+        Builtin::new("bitOr", &[true, true], |args, _| {
+            Ok(Value::Integer(args[0].as_int()? | args[1].as_int()?))
         }),
-        Builtin::new("bitXor", 2, |args, vm| {
-            let x = args[0].force(vm)?;
-            let y = args[1].force(vm)?;
-            Ok(Value::Integer(x.as_int()? ^ y.as_int()?))
+        Builtin::new("bitXor", &[true, true], |args, _| {
+            Ok(Value::Integer(args[0].as_int()? ^ args[1].as_int()?))
         }),
-        Builtin::new("catAttrs", 2, |mut args, _| {
+        Builtin::new("catAttrs", &[true, true], |mut args, _| {
             let list = args.pop().unwrap().to_list()?;
             let key = args.pop().unwrap().to_str()?;
             let mut output = vec![];
@@ -110,10 +102,10 @@ fn pure_builtins() -> Vec<Builtin> {
 
             Ok(Value::List(NixList::construct(output.len(), output)))
         }),
-        Builtin::new("compareVersions", 2, |mut args, vm| {
-            let s1 = args[0].force(vm)?.to_str()?;
+        Builtin::new("compareVersions", &[true, true], |args, _| {
+            let s1 = args[0].to_str()?;
             let s1 = VersionPartsIter::new(s1.as_str());
-            let s2 = args[1].force(vm)?.to_str()?;
+            let s2 = args[1].to_str()?;
             let s2 = VersionPartsIter::new(s2.as_str());
 
             match s1.cmp(s2) {
@@ -122,14 +114,13 @@ fn pure_builtins() -> Vec<Builtin> {
                 std::cmp::Ordering::Greater => Ok(Value::Integer(-1)),
             }
         }),
-        Builtin::new("div", 2, |mut args, _| {
+        Builtin::new("div", &[true, true], |mut args, _| {
             let b = args.pop().unwrap();
             let a = args.pop().unwrap();
             arithmetic_op!(a, b, /)
         }),
-        Builtin::new("elemAt", 2, |args, vm| {
-            let value = args[0].force(vm)?;
-            let xs = value.to_list()?;
+        Builtin::new("elemAt", &[true, true], |args, _| {
+            let xs = args[0].to_list()?;
             let i = args[1].as_int()?;
             if i < 0 {
                 Err(ErrorKind::IndexOutOfBounds { index: i })
@@ -140,63 +131,57 @@ fn pure_builtins() -> Vec<Builtin> {
                 }
             }
         }),
-        Builtin::new("length", 1, |args, vm| {
-            if let Value::Thunk(t) = &args[0] {
-                t.force(vm)?;
-            }
+        Builtin::new("length", &[true], |args, _| {
             Ok(Value::Integer(args[0].to_list()?.len() as i64))
         }),
-        Builtin::new("head", 1, |args, vm| {
-            let xs = args[0].force(vm)?;
-            match xs.to_list()?.get(0) {
-                Some(x) => Ok(x.clone()),
-                None => Err(ErrorKind::IndexOutOfBounds { index: 0 }),
-            }
+        Builtin::new("head", &[true], |args, _| match args[0].to_list()?.get(0) {
+            Some(x) => Ok(x.clone()),
+            None => Err(ErrorKind::IndexOutOfBounds { index: 0 }),
         }),
-        Builtin::new("isAttrs", 1, |args, _| {
+        Builtin::new("isAttrs", &[true], |args, _| {
             Ok(Value::Bool(matches!(args[0], Value::Attrs(_))))
         }),
-        Builtin::new("isBool", 1, |args, _| {
+        Builtin::new("isBool", &[true], |args, _| {
             Ok(Value::Bool(matches!(args[0], Value::Bool(_))))
         }),
-        Builtin::new("isFloat", 1, |args, _| {
+        Builtin::new("isFloat", &[true], |args, _| {
             Ok(Value::Bool(matches!(args[0], Value::Float(_))))
         }),
-        Builtin::new("isFunction", 1, |args, _| {
+        Builtin::new("isFunction", &[true], |args, _| {
             Ok(Value::Bool(matches!(
                 args[0],
                 Value::Closure(_) | Value::Builtin(_)
             )))
         }),
-        Builtin::new("isInt", 1, |args, _| {
+        Builtin::new("isInt", &[true], |args, _| {
             Ok(Value::Bool(matches!(args[0], Value::Integer(_))))
         }),
-        Builtin::new("isList", 1, |args, _| {
+        Builtin::new("isList", &[true], |args, _| {
             Ok(Value::Bool(matches!(args[0], Value::List(_))))
         }),
-        Builtin::new("isNull", 1, |args, _| {
+        Builtin::new("isNull", &[true], |args, _| {
             Ok(Value::Bool(matches!(args[0], Value::Null)))
         }),
-        Builtin::new("isPath", 1, |args, _| {
+        Builtin::new("isPath", &[true], |args, _| {
             Ok(Value::Bool(matches!(args[0], Value::Path(_))))
         }),
-        Builtin::new("isString", 1, |args, _| {
+        Builtin::new("isString", &[true], |args, _| {
             Ok(Value::Bool(matches!(args[0], Value::String(_))))
         }),
-        Builtin::new("mul", 2, |mut args, _| {
+        Builtin::new("mul", &[true, true], |mut args, _| {
             let b = args.pop().unwrap();
             let a = args.pop().unwrap();
             arithmetic_op!(a, b, *)
         }),
-        Builtin::new("sub", 2, |mut args, _| {
+        Builtin::new("sub", &[true, true], |mut args, _| {
             let b = args.pop().unwrap();
             let a = args.pop().unwrap();
             arithmetic_op!(a, b, -)
         }),
-        Builtin::new("substring", 3, |args, vm| {
-            let beg = args[0].force(vm)?.as_int()?;
-            let len = args[1].force(vm)?.as_int()?;
-            let x = args[2].force(vm)?.to_str()?;
+        Builtin::new("substring", &[true, true, true], |args, _| {
+            let beg = args[0].as_int()?;
+            let len = args[1].as_int()?;
+            let x = args[2].to_str()?;
 
             if beg < 0 {
                 return Err(ErrorKind::IndexOutOfBounds { index: beg });
@@ -221,8 +206,8 @@ fn pure_builtins() -> Vec<Builtin> {
                 x.as_str()[(beg as usize)..(end as usize)].into(),
             ))
         }),
-        Builtin::new("tail", 1, |args, vm| {
-            let xs = args[0].force(vm)?.to_list()?;
+        Builtin::new("tail", &[true], |args, _| {
+            let xs = args[0].to_list()?;
 
             if xs.len() == 0 {
                 Err(ErrorKind::TailEmptyList)
@@ -231,17 +216,20 @@ fn pure_builtins() -> Vec<Builtin> {
                 Ok(Value::List(NixList::construct(output.len(), output)))
             }
         }),
-        Builtin::new("throw", 1, |mut args, _| {
+        Builtin::new("throw", &[true], |mut args, _| {
             return Err(ErrorKind::Throw(
                 args.pop().unwrap().to_str()?.as_str().to_owned(),
             ));
         }),
-        Builtin::new("toString", 1, |args, vm| {
+        Builtin::new("toString", &[true], |args, vm| {
             args[0]
                 .coerce_to_string(CoercionKind::Strong, vm)
                 .map(Value::String)
         }),
-        Builtin::new("typeOf", 1, |args, vm| {
+        Builtin::new("typeOf", &[false], |args, vm| {
+            // We force manually here because it also unwraps the Thunk
+            // representation, if any.
+            // TODO(sterni): it'd be nice if we didn't have to worry about this
             let value = args[0].force(vm)?;
             Ok(Value::String(value.type_of().into()))
         }),