Cherry-pick PR microsoft#36663 into release-3.8

Component commits:
6aaf984 Allow intersections (and substitutions) to be checks against discriminable unions

Author: weswigham

Diff for: src/compiler/checker.ts

@@ -15842,7 +15842,7 @@ namespace ts {
                     // with respect to T. We do not report errors here, as we will use the existing
                     // error result from checking each constituent of the union.
                     if (source.flags & (TypeFlags.Object | TypeFlags.Intersection) && target.flags & TypeFlags.Union) {
-                        const objectOnlyTarget = extractTypesOfKind(target, TypeFlags.Object);
+                        const objectOnlyTarget = extractTypesOfKind(target, TypeFlags.Object | TypeFlags.Intersection | TypeFlags.Substitution);
                         if (objectOnlyTarget.flags & TypeFlags.Union) {
                             const result = typeRelatedToDiscriminatedType(source, objectOnlyTarget as UnionType);
                             if (result) {
@@ -15939,7 +15939,7 @@ namespace ts {
                 // NOTE: See ~/tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithDiscriminatedUnion.ts
                 //       for examples.
 
-                const sourceProperties = getPropertiesOfObjectType(source);
+                const sourceProperties = getPropertiesOfType(source);
                 const sourcePropertiesFiltered = findDiscriminantProperties(sourceProperties, target);
                 if (!sourcePropertiesFiltered) return Ternary.False;
 
@@ -15978,7 +15978,7 @@ namespace ts {
                     outer: for (const type of target.types) {
                         for (let i = 0; i < sourcePropertiesFiltered.length; i++) {
                             const sourceProperty = sourcePropertiesFiltered[i];
-                            const targetProperty = getPropertyOfObjectType(type, sourceProperty.escapedName);
+                            const targetProperty = getPropertyOfType(type, sourceProperty.escapedName);
                             if (!targetProperty) continue outer;
                             if (sourceProperty === targetProperty) continue;
                             // We compare the source property to the target in the context of a single discriminant type.

Diff for: tests/baselines/reference/discriminableUnionWithIntersectedMembers.js

@@ -0,0 +1,21 @@
+//// [discriminableUnionWithIntersectedMembers.ts]
+// regression test for https://github.com/microsoft/TypeScript/issues/33243
+type X = 
+ | { x: 'x', y: number } & { y: number } 
+ | { x: 'y', y: number, z?: boolean } & { y: number }
+
+// error
+const x: X = 4 as any as { x: 'x' | 'y', y: number };
+
+type Y = 
+ | { x: 'x', y: number } 
+ | { x: 'y', y: number, z?: boolean }
+
+// no  error
+const y: Y = 4 as any as { x: 'x' | 'y', y: number };
+
+//// [discriminableUnionWithIntersectedMembers.js]
+// error
+var x = 4;
+// no  error
+var y = 4;

Diff for: tests/baselines/reference/discriminableUnionWithIntersectedMembers.symbols

@@ -0,0 +1,42 @@
+=== tests/cases/compiler/discriminableUnionWithIntersectedMembers.ts ===
+// regression test for https://github.com/microsoft/TypeScript/issues/33243
+type X = 
+>X : Symbol(X, Decl(discriminableUnionWithIntersectedMembers.ts, 0, 0))
+
+ | { x: 'x', y: number } & { y: number } 
+>x : Symbol(x, Decl(discriminableUnionWithIntersectedMembers.ts, 2, 4))
+>y : Symbol(y, Decl(discriminableUnionWithIntersectedMembers.ts, 2, 12))
+>y : Symbol(y, Decl(discriminableUnionWithIntersectedMembers.ts, 2, 28))
+
+ | { x: 'y', y: number, z?: boolean } & { y: number }
+>x : Symbol(x, Decl(discriminableUnionWithIntersectedMembers.ts, 3, 4))
+>y : Symbol(y, Decl(discriminableUnionWithIntersectedMembers.ts, 3, 12))
+>z : Symbol(z, Decl(discriminableUnionWithIntersectedMembers.ts, 3, 23))
+>y : Symbol(y, Decl(discriminableUnionWithIntersectedMembers.ts, 3, 41))
+
+// error
+const x: X = 4 as any as { x: 'x' | 'y', y: number };
+>x : Symbol(x, Decl(discriminableUnionWithIntersectedMembers.ts, 6, 5))
+>X : Symbol(X, Decl(discriminableUnionWithIntersectedMembers.ts, 0, 0))
+>x : Symbol(x, Decl(discriminableUnionWithIntersectedMembers.ts, 6, 26))
+>y : Symbol(y, Decl(discriminableUnionWithIntersectedMembers.ts, 6, 40))
+
+type Y = 
+>Y : Symbol(Y, Decl(discriminableUnionWithIntersectedMembers.ts, 6, 53))
+
+ | { x: 'x', y: number } 
+>x : Symbol(x, Decl(discriminableUnionWithIntersectedMembers.ts, 9, 4))
+>y : Symbol(y, Decl(discriminableUnionWithIntersectedMembers.ts, 9, 12))
+
+ | { x: 'y', y: number, z?: boolean }
+>x : Symbol(x, Decl(discriminableUnionWithIntersectedMembers.ts, 10, 4))
+>y : Symbol(y, Decl(discriminableUnionWithIntersectedMembers.ts, 10, 12))
+>z : Symbol(z, Decl(discriminableUnionWithIntersectedMembers.ts, 10, 23))
+
+// no  error
+const y: Y = 4 as any as { x: 'x' | 'y', y: number };
+>y : Symbol(y, Decl(discriminableUnionWithIntersectedMembers.ts, 13, 5))
+>Y : Symbol(Y, Decl(discriminableUnionWithIntersectedMembers.ts, 6, 53))
+>x : Symbol(x, Decl(discriminableUnionWithIntersectedMembers.ts, 13, 26))
+>y : Symbol(y, Decl(discriminableUnionWithIntersectedMembers.ts, 13, 40))
+

Diff for: tests/baselines/reference/discriminableUnionWithIntersectedMembers.types

@@ -0,0 +1,46 @@
+=== tests/cases/compiler/discriminableUnionWithIntersectedMembers.ts ===
+// regression test for https://github.com/microsoft/TypeScript/issues/33243
+type X = 
+>X : X
+
+ | { x: 'x', y: number } & { y: number } 
+>x : "x"
+>y : number
+>y : number
+
+ | { x: 'y', y: number, z?: boolean } & { y: number }
+>x : "y"
+>y : number
+>z : boolean
+>y : number
+
+// error
+const x: X = 4 as any as { x: 'x' | 'y', y: number };
+>x : X
+>4 as any as { x: 'x' | 'y', y: number } : { x: "x" | "y"; y: number; }
+>4 as any : any
+>4 : 4
+>x : "x" | "y"
+>y : number
+
+type Y = 
+>Y : Y
+
+ | { x: 'x', y: number } 
+>x : "x"
+>y : number
+
+ | { x: 'y', y: number, z?: boolean }
+>x : "y"
+>y : number
+>z : boolean
+
+// no  error
+const y: Y = 4 as any as { x: 'x' | 'y', y: number };
+>y : Y
+>4 as any as { x: 'x' | 'y', y: number } : { x: "x" | "y"; y: number; }
+>4 as any : any
+>4 : 4
+>x : "x" | "y"
+>y : number
+

Diff for: tests/cases/compiler/discriminableUnionWithIntersectedMembers.ts

@@ -0,0 +1,14 @@
+// regression test for https://github.com/microsoft/TypeScript/issues/33243
+type X = 
+ | { x: 'x', y: number } & { y: number } 
+ | { x: 'y', y: number, z?: boolean } & { y: number }
+
+// error
+const x: X = 4 as any as { x: 'x' | 'y', y: number };
+
+type Y = 
+ | { x: 'x', y: number } 
+ | { x: 'y', y: number, z?: boolean }
+
+// no  error
+const y: Y = 4 as any as { x: 'x' | 'y', y: number };