Improve type discrimination algorithm

internal/checker/relater.go

@@ -1217,10 +1217,12 @@ func (c *Checker) discriminateTypeByDiscriminableItems(target *Type, discriminat
 		for i := range types {
 			if include[i] != TernaryFalse {
 				targetType := c.getTypeOfPropertyOrIndexSignatureOfType(types[i], discriminator.name(n))
-				if targetType != nil && discriminator.matches(n, targetType) {
-					matched = true
-				} else {
-					include[i] = TernaryMaybe
+				if targetType != nil {
+					if discriminator.matches(n, targetType) {
+						matched = true
+					} else {
+						include[i] = TernaryMaybe
+					}
 				}
 			}
 		}

testdata/baselines/reference/compiler/missingDiscriminants.errors.txt

@@ -0,0 +1,28 @@
+missingDiscriminants.ts(17,23): error TS2353: Object literal may only specify known properties, and 'subkind' does not exist in type '{ kind: "b"; }'.
+missingDiscriminants.ts(18,34): error TS2353: Object literal may only specify known properties, and 'subkind' does not exist in type '{ kind: "b"; }'.
+
+
+==== missingDiscriminants.ts (2 errors) ====
+    // https://github.com/microsoft/typescript-go/issues/1020
+
+    type Thing =
+      | { str: "a", num: 0 }
+      | { str: "b" }
+      | { num: 1 }
+
+    const thing1: Thing = { str: "a", num: 0 }
+    const thing2: Thing = { str: "b", num: 1 } // Shouldn't be error
+    const thing3: Thing = { num: 1, str: "b" } // Shouldn't be error
+
+    type Item =
+      | { kind: "a", subkind: 0, value: string }
+      | { kind: "a", subkind: 1, value: number }
+      | { kind: "b" }
+
+    const item1: Item = { subkind: 1, kind: "b" } // Error, type "b" not assignable to type "a"
+                          ~~~~~~~
+!!! error TS2353: Object literal may only specify known properties, and 'subkind' does not exist in type '{ kind: "b"; }'.
+    const item2: Item = { kind: "b", subkind: 1 } // Error, 'subkind' isn't a known property
+                                     ~~~~~~~
+!!! error TS2353: Object literal may only specify known properties, and 'subkind' does not exist in type '{ kind: "b"; }'.
+

testdata/baselines/reference/compiler/missingDiscriminants.symbols

@@ -0,0 +1,64 @@
+//// [tests/cases/compiler/missingDiscriminants.ts] ////
+
+=== missingDiscriminants.ts ===
+// https://github.com/microsoft/typescript-go/issues/1020
+
+type Thing =
+>Thing : Symbol(Thing, Decl(missingDiscriminants.ts, 0, 0))
+
+  | { str: "a", num: 0 }
+>str : Symbol(str, Decl(missingDiscriminants.ts, 3, 5))
+>num : Symbol(num, Decl(missingDiscriminants.ts, 3, 15))
+
+  | { str: "b" }
+>str : Symbol(str, Decl(missingDiscriminants.ts, 4, 5))
+
+  | { num: 1 }
+>num : Symbol(num, Decl(missingDiscriminants.ts, 5, 5))
+
+const thing1: Thing = { str: "a", num: 0 }
+>thing1 : Symbol(thing1, Decl(missingDiscriminants.ts, 7, 5))
+>Thing : Symbol(Thing, Decl(missingDiscriminants.ts, 0, 0))
+>str : Symbol(str, Decl(missingDiscriminants.ts, 7, 23))
+>num : Symbol(num, Decl(missingDiscriminants.ts, 7, 33))
+
+const thing2: Thing = { str: "b", num: 1 } // Shouldn't be error
+>thing2 : Symbol(thing2, Decl(missingDiscriminants.ts, 8, 5))
+>Thing : Symbol(Thing, Decl(missingDiscriminants.ts, 0, 0))
+>str : Symbol(str, Decl(missingDiscriminants.ts, 8, 23))
+>num : Symbol(num, Decl(missingDiscriminants.ts, 8, 33))
+
+const thing3: Thing = { num: 1, str: "b" } // Shouldn't be error
+>thing3 : Symbol(thing3, Decl(missingDiscriminants.ts, 9, 5))
+>Thing : Symbol(Thing, Decl(missingDiscriminants.ts, 0, 0))
+>num : Symbol(num, Decl(missingDiscriminants.ts, 9, 23))
+>str : Symbol(str, Decl(missingDiscriminants.ts, 9, 31))
+
+type Item =
+>Item : Symbol(Item, Decl(missingDiscriminants.ts, 9, 42))
+
+  | { kind: "a", subkind: 0, value: string }
+>kind : Symbol(kind, Decl(missingDiscriminants.ts, 12, 5))
+>subkind : Symbol(subkind, Decl(missingDiscriminants.ts, 12, 16))
+>value : Symbol(value, Decl(missingDiscriminants.ts, 12, 28))
+
+  | { kind: "a", subkind: 1, value: number }
+>kind : Symbol(kind, Decl(missingDiscriminants.ts, 13, 5))
+>subkind : Symbol(subkind, Decl(missingDiscriminants.ts, 13, 16))
+>value : Symbol(value, Decl(missingDiscriminants.ts, 13, 28))
+
+  | { kind: "b" }
+>kind : Symbol(kind, Decl(missingDiscriminants.ts, 14, 5))
+
+const item1: Item = { subkind: 1, kind: "b" } // Error, type "b" not assignable to type "a"
+>item1 : Symbol(item1, Decl(missingDiscriminants.ts, 16, 5))
+>Item : Symbol(Item, Decl(missingDiscriminants.ts, 9, 42))
+>subkind : Symbol(subkind, Decl(missingDiscriminants.ts, 16, 21))
+>kind : Symbol(kind, Decl(missingDiscriminants.ts, 16, 33))
+
+const item2: Item = { kind: "b", subkind: 1 } // Error, 'subkind' isn't a known property
+>item2 : Symbol(item2, Decl(missingDiscriminants.ts, 17, 5))
+>Item : Symbol(Item, Decl(missingDiscriminants.ts, 9, 42))
+>kind : Symbol(kind, Decl(missingDiscriminants.ts, 17, 21))
+>subkind : Symbol(subkind, Decl(missingDiscriminants.ts, 17, 32))
+

testdata/baselines/reference/compiler/missingDiscriminants.types

@@ -0,0 +1,74 @@
+//// [tests/cases/compiler/missingDiscriminants.ts] ////
+
+=== missingDiscriminants.ts ===
+// https://github.com/microsoft/typescript-go/issues/1020
+
+type Thing =
+>Thing : Thing
+
+  | { str: "a", num: 0 }
+>str : "a"
+>num : 0
+
+  | { str: "b" }
+>str : "b"
+
+  | { num: 1 }
+>num : 1
+
+const thing1: Thing = { str: "a", num: 0 }
+>thing1 : Thing
+>{ str: "a", num: 0 } : { str: "a"; num: 0; }
+>str : "a"
+>"a" : "a"
+>num : 0
+>0 : 0
+
+const thing2: Thing = { str: "b", num: 1 } // Shouldn't be error
+>thing2 : Thing
+>{ str: "b", num: 1 } : { str: "b"; num: 1; }
+>str : "b"
+>"b" : "b"
+>num : 1
+>1 : 1
+
+const thing3: Thing = { num: 1, str: "b" } // Shouldn't be error
+>thing3 : Thing
+>{ num: 1, str: "b" } : { num: 1; str: "b"; }
+>num : 1
+>1 : 1
+>str : "b"
+>"b" : "b"
+
+type Item =
+>Item : Item
+
+  | { kind: "a", subkind: 0, value: string }
+>kind : "a"
+>subkind : 0
+>value : string
+
+  | { kind: "a", subkind: 1, value: number }
+>kind : "a"
+>subkind : 1
+>value : number
+
+  | { kind: "b" }
+>kind : "b"
+
+const item1: Item = { subkind: 1, kind: "b" } // Error, type "b" not assignable to type "a"
+>item1 : Item
+>{ subkind: 1, kind: "b" } : { subkind: number; kind: "b"; }
+>subkind : number
+>1 : 1
+>kind : "b"
+>"b" : "b"
+
+const item2: Item = { kind: "b", subkind: 1 } // Error, 'subkind' isn't a known property
+>item2 : Item
+>{ kind: "b", subkind: 1 } : { kind: "b"; subkind: number; }
+>kind : "b"
+>"b" : "b"
+>subkind : number
+>1 : 1
+

testdata/baselines/reference/submodule/compiler/discriminateWithMissingProperty.errors.txt.diff

@@ -0,0 +1,26 @@
+--- old.discriminateWithMissingProperty.errors.txt
++++ new.discriminateWithMissingProperty.errors.txt
+@@= skipped -0, +0 lines =@@
+-discriminateWithMissingProperty.ts(12,5): error TS2345: Argument of type '{ mode: "numeric"; data: Uint8Array<ArrayBuffer>; }' is not assignable to parameter of type 'Arg'.
+-  Types of property 'data' are incompatible.
+-    Type 'Uint8Array<ArrayBuffer>' is not assignable to type 'number'.
+-
+-
+-==== discriminateWithMissingProperty.ts (1 errors) ====
+-    type Arg = {
+-        mode: "numeric",
+-        data: number,
+-    } | {
+-        mode: "alphabetic",
+-        data: string,
+-    } | {
+-        data: string | Uint8Array;
+-    }
+-    
+-    declare function foo(arg: Arg): void;
+-    foo({ mode: "numeric", data: new Uint8Array([30]) }); // Should error
+-        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+-!!! error TS2345: Argument of type '{ mode: "numeric"; data: Uint8Array<ArrayBuffer>; }' is not assignable to parameter of type 'Arg'.
+-!!! error TS2345:   Types of property 'data' are incompatible.
+-!!! error TS2345:     Type 'Uint8Array<ArrayBuffer>' is not assignable to type 'number'.
++<no content>

testdata/tests/cases/compiler/missingDiscriminants.ts

@@ -0,0 +1,21 @@
+// @strict: true
+// @noEmit: true
+
+// https://github.com/microsoft/typescript-go/issues/1020
+
+type Thing =
+  | { str: "a", num: 0 }
+  | { str: "b" }
+  | { num: 1 }
+
+const thing1: Thing = { str: "a", num: 0 }
+const thing2: Thing = { str: "b", num: 1 } // Shouldn't be error
+const thing3: Thing = { num: 1, str: "b" } // Shouldn't be error
+
+type Item =
+  | { kind: "a", subkind: 0, value: string }
+  | { kind: "a", subkind: 1, value: number }
+  | { kind: "b" }
+
+const item1: Item = { subkind: 1, kind: "b" } // Error, type "b" not assignable to type "a"
+const item2: Item = { kind: "b", subkind: 1 } // Error, 'subkind' isn't a known property