Correct infinity comparisons and toNumber

src/util/cast.js

@@ -30,6 +30,7 @@ class Cast {
     static toNumber (value) {
         // If value is already a number we don't need to coerce it with
         // Number().
+
         if (typeof value === 'number') {
             // Scratch treats NaN as 0, when needed as a number.
             // E.g., 0 + NaN -> 0.
@@ -38,8 +39,14 @@ class Cast {
             }
             return value;
         }
-
-        const n = Number(value);
+        let n;
+        if (Cast.isInfinity(value)) {
+            n = Infinity;
+        } else if (Cast.isNegativeInfinity(value)) {
+            n = -Infinity;
+        } else {
+            n = Number(value);
+        }
         if (_NumberIsNaN(n)) {
             // Scratch treats NaN as 0, when needed as a number.
             // E.g., 0 + NaN -> 0.
@@ -117,6 +124,24 @@ class Cast {
         return val === null || (typeof val === 'string' && val.trim().length === 0);
     }
 
+    /**
+     * Determine if a Scratch argument is infinity.
+     * @param {*} val value to check.
+     * @return {boolean} True if the argument is any capitalization of infinity.
+     */
+    static isInfinity (val) {
+        return val === Infinity || (typeof val === 'string' && val.toLowerCase() === 'infinity');
+    }
+
+    /**
+     * Determine if a Scratch argument is negative infinity.
+     * @param {*} val value to check.
+     * @return {boolean} True if the argument is a '-' folled by any capitalization of infinity.
+     */
+    static isNegativeInfinity (val) {
+        return val === -Infinity || (typeof val === 'string' && val.toLowerCase() === '-infinity');
+    }
+
     /**
      * Compare two values, using Scratch cast, case-insensitive string compare, etc.
      * In Scratch 2.0, this is captured by `interp.compare.`
@@ -125,8 +150,10 @@ class Cast {
      * @returns {number} Negative number if v1 < v2; 0 if equal; positive otherwise.
      */
     static compare (v1, v2) {
-        let n1 = Number(v1);
-        let n2 = Number(v2);
+        // If Cast.toNumber returns '0', then the value might be NaN. If the value is NaN,
+        // this comparison algorithm needs to know.
+        let n1 = Cast.toNumber(v1) || Number(v1);
+        let n2 = Cast.toNumber(v2) || Number(v2);
         if (n1 === 0 && Cast.isWhiteSpace(v1)) {
             n1 = NaN;
         } else if (n2 === 0 && Cast.isWhiteSpace(v2)) {
@@ -145,8 +172,16 @@ class Cast {
             return 0;
         }
         // Compare as numbers.
-        return n1 - n2;
-
+        const r = n1 - n2;
+        if (isNaN(r)) {
+            if (n1 === Infinity && n2 === Infinity) {
+                return 0;
+            }
+            if (n1 === -Infinity && n2 === -Infinity) {
+                return 0;
+            }
+        }
+        return r;
     }
 
     /**