fix(sql): reject procedural division/modulo by zero (#227)

The procedural executor's constant-expression evaluator — a separate,
sqlparser-based tree-walk evaluator used by trigger bodies and
EXCEPTION blocks, with no dependency on the DataFusion-backed
row-expression evaluator — still folded `/` and `%` by a zero divisor
to NULL instead of raising an error. A trigger computing
`NEW.ratio := NEW.numerator / NEW.denominator` would silently write
NULL when the denominator was zero instead of failing the insert.

try_eval_constant, eval_expr, and eval_binary_op now return
Result<Option<Value>, ConstEvalError> instead of Option<Value>, and
raise a division-by-zero signal only when a `/` or `%` reaches a zero
divisor; every other historically-NULL-folding case (unknown
identifiers, unsupported operators, overflow, non-finite float
results) keeps folding to None as before. The signal converts to a
new crate::Error::DivisionByZero variant, which pgwire renders as
SQLSTATE 22012 (division_by_zero), so trigger bodies can also match
it with EXCEPTION WHEN DIVISION_BY_ZERO.

Add the supporting DivisionByZero plumbing at the nodedb-types layer
(ErrorCode, ErrorDetails, msgpack wire tag, SQLSTATE constant,
NodeDbError constructor) and e2e coverage: a BEFORE INSERT trigger
dividing by zero rejects the insert without persisting the row, a
non-zero divisor still computes and persists normally, and an
EXCEPTION WHEN DIVISION_BY_ZERO handler catches the signal and lets
the insert proceed with its fallback assignment.

Author: emanzx

nodedb-types/src/error/code.rs

@@ -43,6 +43,8 @@ impl ErrorCode {
     pub const PLAN_ERROR: Self = Self(1200);
     pub const FAN_OUT_EXCEEDED: Self = Self(1201);
     pub const SQL_NOT_ENABLED: Self = Self(1202);
+    /// Expression evaluation divided or took a modulus by zero.
+    pub const DIVISION_BY_ZERO: Self = Self(1204);
 
     // Engine ops (1300–1399)
     pub const ARRAY: Self = Self(1300);

nodedb-types/src/error/ctors/read_query_auth.rs

@@ -120,6 +120,19 @@ impl NodeDbError {
         }
     }
 
+    /// Expression evaluation divided or took a modulus by zero. Distinct
+    /// from `plan_error` so clients can match on the specific code
+    /// (SQLSTATE `22012`, `division_by_zero`) rather than parsing the
+    /// message (nodedb issue #216).
+    pub fn division_by_zero() -> Self {
+        Self {
+            code: ErrorCode::DIVISION_BY_ZERO,
+            message: "division by zero".to_string(),
+            details: ErrorDetails::DivisionByZero,
+            cause: None,
+        }
+    }
+
     pub fn authorization_denied(resource: impl Into<String>) -> Self {
         let resource = resource.into();
         Self {

nodedb-types/src/error/details.rs

@@ -80,6 +80,9 @@ pub enum ErrorDetails {
     FanOutExceeded { shards_touched: u16, limit: u16 },
     #[serde(rename = "sql_not_enabled")]
     SqlNotEnabled,
+    /// Expression evaluation divided or took a modulus by zero.
+    #[serde(rename = "division_by_zero")]
+    DivisionByZero,
 
     // Auth
     #[serde(rename = "authorization_denied")]

nodedb-types/src/error/msgpack/constants.rs

@@ -69,6 +69,7 @@
 // |  61 | MoveTenantSnapshotFailed  |
 // |  62 | MoveTenantCutoverFailed   |
 // |  63 | MoveTenantAlreadyAtTarget |
+// |  68 | DivisionByZero            |
 
 pub(super) const TAG_CONSTRAINT_VIOLATION: u16 = 1;
 pub(super) const TAG_WRITE_CONFLICT: u16 = 2;
@@ -136,3 +137,4 @@ pub(super) const TAG_MOVE_TENANT_ALREADY_AT_TARGET: u16 = 63;
 pub(super) const TAG_MIRROR_READ_ONLY: u16 = 64;
 pub(super) const TAG_STALE_READ_NOT_LEADER: u16 = 65;
 pub(super) const TAG_MIRROR_NOT_PROMOTED: u16 = 66;
+pub(super) const TAG_DIVISION_BY_ZERO: u16 = 68;

nodedb-types/src/error/msgpack/decode/from_messagepack.rs

@@ -123,6 +123,10 @@ impl<'a> FromMessagePack<'a> for ErrorDetails {
                 skip_fields(reader, field_count)?;
                 Ok(ErrorDetails::SqlNotEnabled)
             }
+            TAG_DIVISION_BY_ZERO => {
+                skip_fields(reader, field_count)?;
+                Ok(ErrorDetails::DivisionByZero)
+            }
             TAG_AUTHORIZATION_DENIED => {
                 let (resource,) = read1_str(reader, field_count)?;
                 Ok(ErrorDetails::AuthorizationDenied { resource })
@@ -346,6 +350,7 @@ mod tests {
         for v in [
             ErrorDetails::DeadlineExceeded,
             ErrorDetails::SqlNotEnabled,
+            ErrorDetails::DivisionByZero,
             ErrorDetails::AuthExpired,
             ErrorDetails::SyncConnectionFailed,
             ErrorDetails::Config,

nodedb-types/src/error/msgpack/encode.rs

@@ -153,6 +153,7 @@ impl ToMessagePack for ErrorDetails {
                 limit,
             } => write2(writer, TAG_FAN_OUT_EXCEEDED, shards_touched, limit),
             ErrorDetails::SqlNotEnabled => write_unit(writer, TAG_SQL_NOT_ENABLED),
+            ErrorDetails::DivisionByZero => write_unit(writer, TAG_DIVISION_BY_ZERO),
             ErrorDetails::AuthorizationDenied { resource } => {
                 write1(writer, TAG_AUTHORIZATION_DENIED, resource)
             }

nodedb-types/src/error/sqlstate.rs

@@ -40,6 +40,10 @@ pub const CANNOT_DROP_DEFAULT_DATABASE: &str = "0A000";
 /// `22003` — `numeric_value_out_of_range`
 pub const NUMERIC_VALUE_OUT_OF_RANGE: &str = "22003";
 
+/// `22012` — `division_by_zero` (`/` or `%` with a zero divisor; nodedb
+/// issue #216 — raised at runtime instead of evaluating to `NULL`)
+pub const DIVISION_BY_ZERO: &str = "22012";
+
 // ── Class 23 — Integrity Constraint Violation ────────────────────────────────
 
 /// `23000` — `integrity_constraint_violation` (generic)
@@ -237,6 +241,7 @@ mod tests {
             NO_DATA,
             FEATURE_NOT_SUPPORTED,
             NUMERIC_VALUE_OUT_OF_RANGE,
+            DIVISION_BY_ZERO,
             INTEGRITY_CONSTRAINT_VIOLATION,
             NOT_NULL_VIOLATION,
             FOREIGN_KEY_VIOLATION,

nodedb-types/src/error/types.rs

@@ -98,6 +98,7 @@ impl NodeDbError {
                 | ErrorDetails::AuthExpired
                 | ErrorDetails::Config
                 | ErrorDetails::SqlNotEnabled
+                | ErrorDetails::DivisionByZero
         )
     }
 }