numbers: Add proper safety to operator overloading (#204)

* numbers: Add null assertions to operator overloading

When operator overloading functions are called, then unfortunately
work when the left hand side of the operation is nullable (only inside
class properties), like this:

```ts
class BigInt extends Uint8Array {
    @operator('+')
    plus(other: BigInt): BigInt {
        // ...
    }
}

class Wrapper {
    public constructor(
        public n: BigInt | null
    ) {}
}

let x = BigInt.fromI32(2);
let y: BigInt | null = null;

// x + y; // give compile time error about nullability

let wrapper = new Wrapper(y);

wrapper.n = wrapper.n + x; // doesn't give compile time errors as it should
```

In our case it would break in graph-node's runtime side because these
operator implementations are written there in the host-exports.

These checks only exist while the compiler doesn't catch this itself.

* 0.22.0-alpha.3

Author: evaporei

common/numbers.ts

@@ -137,21 +137,25 @@ export class BigInt extends Uint8Array {
 
   @operator('+')
   plus(other: BigInt): BigInt {
+    assert(this !== null, "Failed to sum BigInts because left hand side is 'null'");
     return bigInt.plus(this, other)
   }
 
   @operator('-')
   minus(other: BigInt): BigInt {
+    assert(this !== null, "Failed to subtract BigInts because left hand side is 'null'");
     return bigInt.minus(this, other)
   }
 
   @operator('*')
   times(other: BigInt): BigInt {
+    assert(this !== null, "Failed to multiply BigInts because left hand side is 'null'");
     return bigInt.times(this, other)
   }
 
   @operator('/')
   div(other: BigInt): BigInt {
+    assert(this !== null, "Failed to divide BigInts because left hand side is 'null'");
     return bigInt.dividedBy(this, other)
   }
 
@@ -161,6 +165,7 @@ export class BigInt extends Uint8Array {
 
   @operator('%')
   mod(other: BigInt): BigInt {
+    assert(this !== null, "Failed to apply module to BigInt because left hand side is 'null'");
     return bigInt.mod(this, other)
   }
 
@@ -319,21 +324,25 @@ export class BigDecimal {
 
   @operator('+')
   plus(other: BigDecimal): BigDecimal {
+    assert(this !== null, "Failed to sum BigDecimals because left hand side is 'null'");
     return bigDecimal.plus(this, other)
   }
 
   @operator('-')
   minus(other: BigDecimal): BigDecimal {
+    assert(this !== null, "Failed to subtract BigDecimals because left hand side is 'null'");
     return bigDecimal.minus(this, other)
   }
 
   @operator('*')
   times(other: BigDecimal): BigDecimal {
+    assert(this !== null, "Failed to multiply BigDecimals because left hand side is 'null'");
     return bigDecimal.times(this, other)
   }
 
   @operator('/')
   div(other: BigDecimal): BigDecimal {
+    assert(this !== null, "Failed to divide BigDecimals because left hand side is 'null'");
     return bigDecimal.dividedBy(this, other)
   }
 
@@ -369,6 +378,7 @@ export class BigDecimal {
 
   @operator.prefix('-')
   neg(): BigDecimal {
+    assert(this !== null, "Failed to negate BigDecimal because the value of it is 'null'");
     return new BigDecimal(new BigInt(0)) - this
   }
 

package.json

@@ -1,7 +1,7 @@
 {
   "name": "@graphprotocol/graph-ts",
   "description": "TypeScript/AssemblyScript library for writing subgraph mappings for The Graph",
-  "version": "0.22.0-alpha.2",
+  "version": "0.22.0-alpha.3",
   "module": "index.ts",
   "types": "index.ts",
   "main": "index.ts",