feat(tvix/eval): implement binary comparison operators r/4478

This is accomplished by simply delegating to the Rust implementations
of (Partial)Ord and (Partial)Eq, which are implemented for Value and
underlying wrapper types to behave like they do in Nix.

To ease the implementation overhead, a new comparison operator macro
has been added to the VM module.

Incomparable types will raise a new error variant when a comparison is
attempted, containing both supplied types. This mimics the information
carried in the error thrown by C++ Nix.

Change-Id: Ia19634d69119d40722f3ca672387bc3a80096998
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6143
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

20 files changed, 121 insertions, 7 deletions

diff --git a/tvix/eval/src/compiler.rs b/tvix/eval/src/compiler.rs
index d48490dde7a6..6054bd3fdaff 100644
--- a/tvix/eval/src/compiler.rs
+++ b/tvix/eval/src/compiler.rs
@@ -137,6 +137,10 @@ impl Compiler {
             BinOpKind::Div => self.chunk.add_op(OpCode::OpDiv),
             BinOpKind::Update => self.chunk.add_op(OpCode::OpAttrsUpdate),
             BinOpKind::Equal => self.chunk.add_op(OpCode::OpEqual),
+            BinOpKind::Less => self.chunk.add_op(OpCode::OpLess),
+            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::NotEqual => {
                 self.chunk.add_op(OpCode::OpEqual);
diff --git a/tvix/eval/src/errors.rs b/tvix/eval/src/errors.rs
index fb9f3b6ec589..f7f64f4e687a 100644
--- a/tvix/eval/src/errors.rs
+++ b/tvix/eval/src/errors.rs
@@ -14,6 +14,11 @@ pub enum Error {
         expected: &'static str,
         actual: &'static str,
     },
+
+    Incomparable {
+        lhs: &'static str,
+        rhs: &'static str,
+    },
 }
 
 impl Display for Error {
diff --git a/tvix/eval/src/opcode.rs b/tvix/eval/src/opcode.rs
index f682cfc8b83f..6800e8411f5c 100644
--- a/tvix/eval/src/opcode.rs
+++ b/tvix/eval/src/opcode.rs
@@ -29,6 +29,10 @@ pub enum OpCode {
 
     // Logical binary operators
     OpEqual,
+    OpLess,
+    OpLessOrEq,
+    OpMore,
+    OpMoreOrEq,
 
     // Attribute sets
     OpAttrs(usize),
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-float-false.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-float-false.exp
new file mode 100644
index 000000000000..95a0e7378b5e
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-float-false.exp
@@ -0,0 +1 @@
+{ eq = false; ge = false; gt = false; le = false; lt = false; ne = false; }
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-float-false.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-float-false.nix
new file mode 100644
index 000000000000..2b511f56eecb
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-float-false.nix
@@ -0,0 +1,8 @@
+{
+  eq = 6.9 == 4.2;
+  ne = 4.2 != 4.2;
+  lt = 2.5 < 1.5;
+  le = 2.5 <= 1.5;
+  gt = 1.5 > 2.5;
+  ge = 1.5 >= 2.5;
+}
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-float-true.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-float-true.exp
new file mode 100644
index 000000000000..9160829dde78
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-float-true.exp
@@ -0,0 +1 @@
+{ eq = true; ge = true; gt = true; le = true; lt = true; ne = true; }
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-float-true.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-float-true.nix
new file mode 100644
index 000000000000..c505a85b1f3c
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-float-true.nix
@@ -0,0 +1,8 @@
+{
+  eq = 4.2 == 4.2;
+  ne = 6.9 != 4.2;
+  lt = 1.5 < 2.5;
+  le = 2.5 <= 2.5;
+  gt = 2.3 > 1.2;
+  ge = 2.3 >= 2.3;
+}
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-int-false.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-int-false.exp
new file mode 100644
index 000000000000..95a0e7378b5e
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-int-false.exp
@@ -0,0 +1 @@
+{ eq = false; ge = false; gt = false; le = false; lt = false; ne = false; }
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-int-false.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-int-false.nix
new file mode 100644
index 000000000000..7d6b30419fac
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-int-false.nix
@@ -0,0 +1,8 @@
+{
+  eq = 69 == 42;
+  ne = 42 != 42;
+  lt = 2 < 1;
+  le = 2 <= 1;
+  gt = 1 > 2;
+  ge = 1 >= 2;
+}
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-int-true.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-int-true.exp
new file mode 100644
index 000000000000..9160829dde78
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-int-true.exp
@@ -0,0 +1 @@
+{ eq = true; ge = true; gt = true; le = true; lt = true; ne = true; }
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-int-true.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-int-true.nix
new file mode 100644
index 000000000000..0bf474e53fd0
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-int-true.nix
@@ -0,0 +1,8 @@
+{
+  eq = 42 == 42;
+  ne = 69 != 42;
+  lt = 1 < 2;
+  le = 2 <= 2;
+  gt = 2 > 1;
+  ge = 2 >= 2;
+}
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-num-false.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-num-false.exp
new file mode 100644
index 000000000000..95a0e7378b5e
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-num-false.exp
@@ -0,0 +1 @@
+{ eq = false; ge = false; gt = false; le = false; lt = false; ne = false; }
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-num-false.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-num-false.nix
new file mode 100644
index 000000000000..61b206c03376
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-num-false.nix
@@ -0,0 +1,8 @@
+{
+  eq = 6.9 == 4;
+  ne = 4.0 != 4;
+  lt = 2.5 < 1;
+  le = 2 <= 1.5;
+  gt = 1 > 1.1;
+  ge = 1.5 >= 2;
+}
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-num-true.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-num-true.exp
new file mode 100644
index 000000000000..9160829dde78
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-num-true.exp
@@ -0,0 +1 @@
+{ eq = true; ge = true; gt = true; le = true; lt = true; ne = true; }
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-num-true.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-num-true.nix
new file mode 100644
index 000000000000..ad77074710ca
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-num-true.nix
@@ -0,0 +1,8 @@
+{
+  eq = 42.0 == 42;
+  ne = 6.9 != 4;
+  lt = 1.5 < 2;
+  le = 2.0 <= 2.0;
+  gt = 1.1 > 1;
+  ge = 2.3 >= 2.3;
+}
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-str-false.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-str-false.exp
new file mode 100644
index 000000000000..95a0e7378b5e
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-str-false.exp
@@ -0,0 +1 @@
+{ eq = false; ge = false; gt = false; le = false; lt = false; ne = false; }
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-str-false.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-str-false.nix
new file mode 100644
index 000000000000..b5773a21d374
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-str-false.nix
@@ -0,0 +1,8 @@
+{
+  eq = "test" == "not test";
+  ne = "test" != "test";
+  lt = "bcd" < "abc";
+  le = "bcd" <= "abc";
+  gt = "abc" > "bcd";
+  ge = "abc" >= "bcd";
+}
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-str-true.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-str-true.exp
new file mode 100644
index 000000000000..9160829dde78
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-str-true.exp
@@ -0,0 +1 @@
+{ eq = true; ge = true; gt = true; le = true; lt = true; ne = true; }
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-str-true.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-str-true.nix
new file mode 100644
index 000000000000..172d2237e9e2
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-cmp-str-true.nix
@@ -0,0 +1,8 @@
+{
+  eq = "test" == "test";
+  ne = "test" != "not test";
+  lt = "abc" < "bcd";
+  le = "bcd" <= "bcd";
+  gt = "bcd" > "abc";
+  ge = "bcd" >= "bcd";
+}
diff --git a/tvix/eval/src/vm.rs b/tvix/eval/src/vm.rs
index db2f76d73145..30f2c5a4a414 100644
--- a/tvix/eval/src/vm.rs
+++ b/tvix/eval/src/vm.rs
@@ -18,15 +18,14 @@ pub struct VM {
 
 macro_rules! arithmetic_op {
     ( $self:ident, $op:tt ) => {{
-        let result = arithmetic_op!($self.pop(), $self.pop(), $op);
+        let b = $self.pop();
+        let a = $self.pop();
+        let result = arithmetic_op!(a, b, $op);
         $self.push(result);
     }};
 
-    ( $b:expr, $a:expr, $op:tt ) => {{
-        let b = $b;
-        let a = $a;
-
-        match (a, b) {
+    ( $a:ident, $b:ident, $op:tt ) => {{
+        match ($a, $b) {
             (Value::Integer(i1), Value::Integer(i2)) => Value::Integer(i1 $op i2),
             (Value::Float(f1), Value::Float(f2)) => Value::Float(f1 $op f2),
             (Value::Integer(i1), Value::Float(f2)) => Value::Float(i1 as f64 $op f2),
@@ -44,6 +43,31 @@ macro_rules! arithmetic_op {
     }};
 }
 
+macro_rules! cmp_op {
+    ( $self:ident, $op:tt ) => {{
+        let b = $self.pop();
+        let a = $self.pop();
+
+        // Comparable (in terms of ordering) values are numbers and
+        // strings. Numbers need to be coerced similarly to arithmetic
+        // ops if mixed types are encountered.
+        let result = match (a, b) {
+            (Value::Integer(i1), Value::Integer(i2)) => i1 $op i2,
+            (Value::Float(f1), Value::Float(f2)) => f1 $op f2,
+            (Value::Integer(i1), Value::Float(f2)) => (i1 as f64) $op f2,
+            (Value::Float(f1), Value::Integer(i2)) => f1 $op (i2 as f64),
+            (Value::String(s1), Value::String(s2)) => s1 $op s2,
+
+            (lhs, rhs) => return Err(Error::Incomparable {
+                lhs: lhs.type_of(),
+                rhs: rhs.type_of(),
+            }),
+        };
+
+        $self.push(Value::Bool(result));
+    }};
+}
+
 impl VM {
     fn inc_ip(&mut self) -> OpCode {
         let op = self.chunk.code[self.ip];
@@ -74,7 +98,7 @@ impl VM {
                     let result = if let (Value::String(s1), Value::String(s2)) = (&a, &b) {
                         Value::String(s1.concat(s2))
                     } else {
-                        arithmetic_op!(b, a, +)
+                        arithmetic_op!(a, b, +)
                     };
 
                     self.push(result)
@@ -107,6 +131,11 @@ impl VM {
                     self.push(Value::Bool(v1 == v2))
                 }
 
+                OpCode::OpLess => cmp_op!(self, <),
+                OpCode::OpLessOrEq => cmp_op!(self, <=),
+                OpCode::OpMore => cmp_op!(self, >),
+                OpCode::OpMoreOrEq => cmp_op!(self, >=),
+
                 OpCode::OpNull => self.push(Value::Null),
                 OpCode::OpTrue => self.push(Value::Bool(true)),
                 OpCode::OpFalse => self.push(Value::Bool(false)),