Add tests

tests/cases/conformance/types/intersection/intersectionReduction.ts

@@ -1,4 +1,4 @@
-// @strict
+// @strict: false
 
 declare const sym1: unique symbol;
 declare const sym2: unique symbol;
@@ -13,3 +13,46 @@ type T7 = string & 'a' & number & 10 & symbol & typeof sym1;  // never
 
 type T10 = string & ('a' | 'b');  // 'a' | 'b'
 type T11 = (string | number) & ('a' | 10);  // 'a' | 10
+
+type N1 = 'a' & 'b';
+type N2 = { a: string } & null;
+type N3 = { a: string } & undefined;
+type N4 = string & number;
+type N5 = number & object;
+type N6 = symbol & string;
+type N7 = void & string;
+
+type X = { x: string };
+
+type X1 = X | 'a' & 'b';
+type X2 = X | { a: string } & null;
+type X3 = X | { a: string } & undefined;
+type X4 = X | string & number;
+type X5 = X | number & object;
+type X6 = X | symbol & string;
+type X7 = X | void & string;
+
+// Repro from #31663
+
+const x1 = { a: 'foo', b: 42 };
+const x2 = { a: 'foo', b: true };
+
+declare let k: 'a' | 'b';
+
+x1[k] = 'bar' as any;  // Error
+x2[k] = 'bar' as any;  // Error
+
+const enum Tag1 {}
+const enum Tag2 {}
+
+declare let s1: string & Tag1;
+declare let s2: string & Tag2;
+
+declare let t1: string & Tag1 | undefined;
+declare let t2: string & Tag2 | undefined;
+
+s1 = s2;
+s2 = s1;
+
+t1 = t2;
+t2 = t1;

tests/cases/conformance/types/intersection/intersectionReductionStrict.ts

@@ -0,0 +1,58 @@
+// @strict: true
+
+declare const sym1: unique symbol;
+declare const sym2: unique symbol;
+
+type T1 = string & 'a';  // 'a'
+type T2 = 'a' & string & 'b';  // never
+type T3 = number & 10;  // 10
+type T4 = 10 & number & 20;  // never
+type T5 = symbol & typeof sym1;  // typeof sym1
+type T6 = typeof sym1 & symbol & typeof sym2;  // never
+type T7 = string & 'a' & number & 10 & symbol & typeof sym1;  // never
+
+type T10 = string & ('a' | 'b');  // 'a' | 'b'
+type T11 = (string | number) & ('a' | 10);  // 'a' | 10
+
+type N1 = 'a' & 'b';
+type N2 = { a: string } & null;
+type N3 = { a: string } & undefined;
+type N4 = string & number;
+type N5 = number & object;
+type N6 = symbol & string;
+type N7 = void & string;
+
+type X = { x: string };
+
+type X1 = X | 'a' & 'b';
+type X2 = X | { a: string } & null;
+type X3 = X | { a: string } & undefined;
+type X4 = X | string & number;
+type X5 = X | number & object;
+type X6 = X | symbol & string;
+type X7 = X | void & string;
+
+// Repro from #31663
+
+const x1 = { a: 'foo', b: 42 };
+const x2 = { a: 'foo', b: true };
+
+declare let k: 'a' | 'b';
+
+x1[k] = 'bar' as any;  // Error
+x2[k] = 'bar' as any;  // Error
+
+const enum Tag1 {}
+const enum Tag2 {}
+
+declare let s1: string & Tag1;
+declare let s2: string & Tag2;
+
+declare let t1: string & Tag1 | undefined;
+declare let t2: string & Tag2 | undefined;
+
+s1 = s2;
+s2 = s1;
+
+t1 = t2;
+t2 = t1;