Merge pull request #30626 from Microsoft/discriminantFromIntersectionErrors

Better discriminant property errors on intersections

Author: DanielRosenwasser

src/compiler/checker.ts

@@ -12533,8 +12533,8 @@ namespace ts {
 
             // Keep this up-to-date with the same logic within `getApparentTypeOfContextualType`, since they should behave similarly
             function findMatchingDiscriminantType(source: Type, target: Type) {
-                if (target.flags & TypeFlags.Union) {
-                    const sourceProperties = getPropertiesOfObjectType(source);
+                if (target.flags & TypeFlags.Union && source.flags & (TypeFlags.Intersection | TypeFlags.Object)) {
+                    const sourceProperties = getPropertiesOfType(source);
                     if (sourceProperties) {
                         const sourcePropertiesFiltered = findDiscriminantProperties(sourceProperties, target);
                         if (sourcePropertiesFiltered) {

tests/baselines/reference/errorMessageOnIntersectionsWithDiscriminants01.errors.txt

@@ -0,0 +1,22 @@
+tests/cases/compiler/errorMessageOnIntersectionsWithDiscriminants01.ts(8,1): error TS2322: Type 'A' is not assignable to type 'B'.
+  Type '{ test: true; } & { foo: 1; }' is not assignable to type 'B'.
+    Type '{ test: true; } & { foo: 1; }' is not assignable to type '{ test: true; } & { bar: 1; }'.
+      Property 'bar' is missing in type '{ test: true; } & { foo: 1; }' but required in type '{ bar: 1; }'.
+
+
+==== tests/cases/compiler/errorMessageOnIntersectionsWithDiscriminants01.ts (1 errors) ====
+    export type Common = { test: true } | { test: false };
+    export type A = Common & { foo: 1 };
+    export type B = Common & { bar: 1 };
+    
+    declare const a: A;
+    declare let b: B;
+    
+    b = a;
+    ~
+!!! error TS2322: Type 'A' is not assignable to type 'B'.
+!!! error TS2322:   Type '{ test: true; } & { foo: 1; }' is not assignable to type 'B'.
+!!! error TS2322:     Type '{ test: true; } & { foo: 1; }' is not assignable to type '{ test: true; } & { bar: 1; }'.
+!!! error TS2322:       Property 'bar' is missing in type '{ test: true; } & { foo: 1; }' but required in type '{ bar: 1; }'.
+!!! related TS2728 tests/cases/compiler/errorMessageOnIntersectionsWithDiscriminants01.ts:3:28: 'bar' is declared here.
+    

tests/baselines/reference/errorMessageOnIntersectionsWithDiscriminants01.symbols

@@ -0,0 +1,28 @@
+=== tests/cases/compiler/errorMessageOnIntersectionsWithDiscriminants01.ts ===
+export type Common = { test: true } | { test: false };
+>Common : Symbol(Common, Decl(errorMessageOnIntersectionsWithDiscriminants01.ts, 0, 0))
+>test : Symbol(test, Decl(errorMessageOnIntersectionsWithDiscriminants01.ts, 0, 22))
+>test : Symbol(test, Decl(errorMessageOnIntersectionsWithDiscriminants01.ts, 0, 39))
+
+export type A = Common & { foo: 1 };
+>A : Symbol(A, Decl(errorMessageOnIntersectionsWithDiscriminants01.ts, 0, 54))
+>Common : Symbol(Common, Decl(errorMessageOnIntersectionsWithDiscriminants01.ts, 0, 0))
+>foo : Symbol(foo, Decl(errorMessageOnIntersectionsWithDiscriminants01.ts, 1, 26))
+
+export type B = Common & { bar: 1 };
+>B : Symbol(B, Decl(errorMessageOnIntersectionsWithDiscriminants01.ts, 1, 36))
+>Common : Symbol(Common, Decl(errorMessageOnIntersectionsWithDiscriminants01.ts, 0, 0))
+>bar : Symbol(bar, Decl(errorMessageOnIntersectionsWithDiscriminants01.ts, 2, 26))
+
+declare const a: A;
+>a : Symbol(a, Decl(errorMessageOnIntersectionsWithDiscriminants01.ts, 4, 13))
+>A : Symbol(A, Decl(errorMessageOnIntersectionsWithDiscriminants01.ts, 0, 54))
+
+declare let b: B;
+>b : Symbol(b, Decl(errorMessageOnIntersectionsWithDiscriminants01.ts, 5, 11))
+>B : Symbol(B, Decl(errorMessageOnIntersectionsWithDiscriminants01.ts, 1, 36))
+
+b = a;
+>b : Symbol(b, Decl(errorMessageOnIntersectionsWithDiscriminants01.ts, 5, 11))
+>a : Symbol(a, Decl(errorMessageOnIntersectionsWithDiscriminants01.ts, 4, 13))
+

tests/baselines/reference/errorMessageOnIntersectionsWithDiscriminants01.types

@@ -0,0 +1,27 @@
+=== tests/cases/compiler/errorMessageOnIntersectionsWithDiscriminants01.ts ===
+export type Common = { test: true } | { test: false };
+>Common : Common
+>test : true
+>true : true
+>test : false
+>false : false
+
+export type A = Common & { foo: 1 };
+>A : A
+>foo : 1
+
+export type B = Common & { bar: 1 };
+>B : B
+>bar : 1
+
+declare const a: A;
+>a : A
+
+declare let b: B;
+>b : B
+
+b = a;
+>b = a : A
+>b : B
+>a : A
+

tests/cases/compiler/errorMessageOnIntersectionsWithDiscriminants01.ts

@@ -0,0 +1,10 @@
+// @noEmit: true
+
+export type Common = { test: true } | { test: false };
+export type A = Common & { foo: 1 };
+export type B = Common & { bar: 1 };
+
+declare const a: A;
+declare let b: B;
+
+b = a;