fix typechecking for unions of array types (microsoft#10945)

Author: riknoll

pxtcompiler/emitter/emitter.ts

@@ -657,6 +657,14 @@ namespace ts.pxtc {
     }
 
     function isArrayType(t: Type) {
+        if (t.flags & TypeFlags.Union && (t as UnionType).types) {
+            for (const subtype of (t as UnionType).types) {
+                if (!isArrayType(subtype)) {
+                    return false;
+                }
+            }
+            return true;
+        }
         if (!isObjectType(t)) {
             return false;
         }
@@ -701,7 +709,12 @@ namespace ts.pxtc {
 
     function arrayElementType(t: Type, idx = -1): Type {
         if (isArrayType(t))
-            return checkType((<TypeReference>t).typeArguments[0])
+            if (t.flags & TypeFlags.Union) {
+                return checkType(t.getNumberIndexType());
+            }
+            else {
+                return checkType((<TypeReference>t).typeArguments[0])
+            }
         return checker.getIndexTypeOfType(t, IndexKind.Number);
     }
 

tests/compile-test/lang-test0/53unionarraytypes.ts

@@ -0,0 +1,6 @@
+let multidim = [[1, 3], ["one", "two"]]
+let a = multidim[0][0]
+let b = multidim[1][1]
+
+assert(a === 1)
+assert(b === "two");

tests/compile-test/lang-test0/pxt.json

@@ -54,6 +54,8 @@
         "49unicode.ts",
         "50indexedtypes.ts",
         "51exceptions.ts",
+        "52parseint.ts",
+        "53unionarraytypes.ts",
         "99final.ts"
     ],
     "public": true,