fix(vrl)!: Make remainder fallible (vectordotdev#11668)

* Make remainder fallible.

Signed-off-by: Stephen Wakely <fungus.humungus@gmail.com>

* Update release notes.

Signed-off-by: Stephen Wakely <fungus.humungus@gmail.com>

* Added test for remainder by zero

Signed-off-by: Stephen Wakely <fungus.humungus@gmail.com>

* Newline

Signed-off-by: Stephen Wakely <fungus.humungus@gmail.com>

* Whitespace

Signed-off-by: Stephen Wakely <fungus.humungus@gmail.com>

lib/vrl/compiler/src/expression/op.rs

@@ -201,6 +201,21 @@ impl Expression for Op {
                 }
             }
 
+            // ... % ...
+            Rem => {
+                // Division is infallible if the rhs is a literal normal float or integer.
+                match self.rhs.as_value() {
+                    Some(value) if lhs_def.is_float() || lhs_def.is_integer() => match value {
+                        Value::Float(v) if v.is_normal() => TypeDef::float().infallible(),
+                        Value::Float(_) => TypeDef::float().fallible(),
+                        Value::Integer(v) if v != 0 => TypeDef::integer().infallible(),
+                        Value::Integer(_) => TypeDef::integer().fallible(),
+                        _ => TypeDef::float().add_integer().fallible(),
+                    },
+                    _ => TypeDef::float().add_integer().fallible(),
+                }
+            }
+
             // "bar" + ...
             // ... + "bar"
             Add if lhs_def.is_bytes() || rhs_def.is_bytes() => lhs_def
@@ -216,7 +231,7 @@ impl Expression for Op {
             // 1.0 - ...
             // 1.0 * ...
             // 1.0 % ...
-            Add | Sub | Mul | Rem if lhs_def.is_float() || rhs_def.is_float() => lhs_def
+            Add | Sub | Mul if lhs_def.is_float() || rhs_def.is_float() => lhs_def
                 .fallible_unless(K::integer().or_float())
                 .merge_deep(rhs_def.fallible_unless(K::integer().or_float()))
                 .with_kind(K::float()),
@@ -225,7 +240,7 @@ impl Expression for Op {
             // 1 - 1
             // 1 * 1
             // 1 % 1
-            Add | Sub | Mul | Rem if lhs_def.is_integer() && rhs_def.is_integer() => {
+            Add | Sub | Mul if lhs_def.is_integer() && rhs_def.is_integer() => {
                 lhs_def.merge_deep(rhs_def).with_kind(K::integer())
             }
 
@@ -247,8 +262,7 @@ impl Expression for Op {
                 .with_kind(K::bytes().or_integer().or_float()),
 
             // ... - ...
-            // ... % ...
-            Sub | Rem => lhs_def
+            Sub => lhs_def
                 .merge_deep(rhs_def)
                 .fallible()
                 .with_kind(K::integer().or_float()),
@@ -579,6 +593,11 @@ mod tests {
             want: TypeDef::integer().infallible(),
         }
 
+        remainder_integer_zero {
+            expr: |_| op(Rem, 5, 0),
+            want: TypeDef::integer().fallible(),
+        }
+
         remainder_float {
             expr: |_| op(Rem, 5.0, 5.0),
             want: TypeDef::float().infallible(),

lib/vrl/compiler/src/value/arithmetic.rs

@@ -176,6 +176,12 @@ impl VrlValueArithmetic for Value {
     fn try_rem(self, rhs: Self) -> Result<Self, Error> {
         let err = || Error::Rem(self.kind(), rhs.kind());
 
+        let rhv = rhs.try_into_f64().map_err(|_| err())?;
+
+        if rhv == 0.0 {
+            return Err(Error::DivideByZero);
+        }
+
         let value = match self {
             Value::Integer(lhv) if rhs.is_float() => {
                 Value::from_f64_or_zero(lhv as f64 % rhs.try_float()?)

lib/vrl/tests/tests/expressions/arithmetic/remainder/zero.vrl

@@ -0,0 +1,4 @@
+# result: 0
+# object: { "zero": 0 }
+
+x = 43 % int!(.zero) ?? 0

website/content/en/highlights/2022-03-22-0-21-0-upgrade-guide.md

@@ -17,6 +17,7 @@ Vector's 0.21.0 release includes **breaking changes**:
 3. [Deprecated GraphQL API subscriptions have been removed](#removed-deprecated-subscriptions)
 4. [The `vector vrl` timezone flag `-tz` is now `-z`](#vector-vrl-timezone)
 5. [The `vector top` human_metrics flag `-h` is now `-H`](#vector-top-human-metrics)
+6. [Remainder operator (%) in VRL is fallible](#remainder-fallible)
 
 And **deprecations**:
 
@@ -151,6 +152,24 @@ v3](https://crates.io/crates/clap), the short `-h` from `--help` and `-h` from
 shortened form for `--human_metrics` is now `-H` and `-h` is reserved for
 `--help`.
 
+#### Remainder operator (%) in VRL is fallible {#remainder-fallible}
+
+The remainder operator in VRL has become a fallible operation. This is because
+finding the remainder with a divisor of zero can raise an error that needs to
+be handled.
+
+Before this VRL would compile:
+
+```coffee
+.remainder = 50 % .value
+```
+
+If `.value` was zero, Vector would panic. This can be fixed by handling the error:
+
+```coffee
+.remainder = 50 % .value ?? 0
+```
+
 ### Deprecations
 
 #### `receivedEventsTotal`, `sentEventsTotal`, `sentEventsThroughput`, `receivedEventsThroughput` subscriptions have been deprecated {#deprecate-aggregate-subscriptions}