Allow (non-assert) type predicates to narrow by discriminant (#57358)

gabritto · web-flow · commit a6414052a3eb · 2024-02-13T11:33:30.000-08:00
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -26743,7 +26743,11 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     function hasMatchingArgument(expression: CallExpression | NewExpression, reference: Node) {
         if (expression.arguments) {
             for (const argument of expression.arguments) {
-                if (isOrContainsMatchingReference(reference, argument) || optionalChainContainsReference(argument, reference)) {
+                if (
+                    isOrContainsMatchingReference(reference, argument)
+                    || optionalChainContainsReference(argument, reference)
+                    || getCandidateDiscriminantPropertyAccess(argument, reference)
+                ) {
                     return true;
                 }
             }
@@ -26757,6 +26761,51 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         return false;
     }
 
+    function getCandidateDiscriminantPropertyAccess(expr: Expression, reference: Node) {
+        if (isBindingPattern(reference) || isFunctionExpressionOrArrowFunction(reference) || isObjectLiteralMethod(reference)) {
+            // When the reference is a binding pattern or function or arrow expression, we are narrowing a pesudo-reference in
+            // getNarrowedTypeOfSymbol. An identifier for a destructuring variable declared in the same binding pattern or
+            // parameter declared in the same parameter list is a candidate.
+            if (isIdentifier(expr)) {
+                const symbol = getResolvedSymbol(expr);
+                const declaration = symbol.valueDeclaration;
+                if (declaration && (isBindingElement(declaration) || isParameter(declaration)) && reference === declaration.parent && !declaration.initializer && !declaration.dotDotDotToken) {
+                    return declaration;
+                }
+            }
+        }
+        else if (isAccessExpression(expr)) {
+            // An access expression is a candidate if the reference matches the left hand expression.
+            if (isMatchingReference(reference, expr.expression)) {
+                return expr;
+            }
+        }
+        else if (isIdentifier(expr)) {
+            const symbol = getResolvedSymbol(expr);
+            if (isConstantVariable(symbol)) {
+                const declaration = symbol.valueDeclaration!;
+                // Given 'const x = obj.kind', allow 'x' as an alias for 'obj.kind'
+                if (
+                    isVariableDeclaration(declaration) && !declaration.type && declaration.initializer && isAccessExpression(declaration.initializer) &&
+                    isMatchingReference(reference, declaration.initializer.expression)
+                ) {
+                    return declaration.initializer;
+                }
+                // Given 'const { kind: x } = obj', allow 'x' as an alias for 'obj.kind'
+                if (isBindingElement(declaration) && !declaration.initializer) {
+                    const parent = declaration.parent.parent;
+                    if (
+                        isVariableDeclaration(parent) && !parent.type && parent.initializer && (isIdentifier(parent.initializer) || isAccessExpression(parent.initializer)) &&
+                        isMatchingReference(reference, parent.initializer)
+                    ) {
+                        return declaration;
+                    }
+                }
+            }
+        }
+        return undefined;
+    }
+
     function getFlowNodeId(flow: FlowNode): number {
         if (!flow.id || flow.id < 0) {
             flow.id = nextFlowId;
@@ -28113,57 +28162,12 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             return result;
         }
 
-        function getCandidateDiscriminantPropertyAccess(expr: Expression) {
-            if (isBindingPattern(reference) || isFunctionExpressionOrArrowFunction(reference) || isObjectLiteralMethod(reference)) {
-                // When the reference is a binding pattern or function or arrow expression, we are narrowing a pesudo-reference in
-                // getNarrowedTypeOfSymbol. An identifier for a destructuring variable declared in the same binding pattern or
-                // parameter declared in the same parameter list is a candidate.
-                if (isIdentifier(expr)) {
-                    const symbol = getResolvedSymbol(expr);
-                    const declaration = symbol.valueDeclaration;
-                    if (declaration && (isBindingElement(declaration) || isParameter(declaration)) && reference === declaration.parent && !declaration.initializer && !declaration.dotDotDotToken) {
-                        return declaration;
-                    }
-                }
-            }
-            else if (isAccessExpression(expr)) {
-                // An access expression is a candidate if the reference matches the left hand expression.
-                if (isMatchingReference(reference, expr.expression)) {
-                    return expr;
-                }
-            }
-            else if (isIdentifier(expr)) {
-                const symbol = getResolvedSymbol(expr);
-                if (isConstantVariable(symbol)) {
-                    const declaration = symbol.valueDeclaration!;
-                    // Given 'const x = obj.kind', allow 'x' as an alias for 'obj.kind'
-                    if (
-                        isVariableDeclaration(declaration) && !declaration.type && declaration.initializer && isAccessExpression(declaration.initializer) &&
-                        isMatchingReference(reference, declaration.initializer.expression)
-                    ) {
-                        return declaration.initializer;
-                    }
-                    // Given 'const { kind: x } = obj', allow 'x' as an alias for 'obj.kind'
-                    if (isBindingElement(declaration) && !declaration.initializer) {
-                        const parent = declaration.parent.parent;
-                        if (
-                            isVariableDeclaration(parent) && !parent.type && parent.initializer && (isIdentifier(parent.initializer) || isAccessExpression(parent.initializer)) &&
-                            isMatchingReference(reference, parent.initializer)
-                        ) {
-                            return declaration;
-                        }
-                    }
-                }
-            }
-            return undefined;
-        }
-
         function getDiscriminantPropertyAccess(expr: Expression, computedType: Type) {
             // As long as the computed type is a subset of the declared type, we use the full declared type to detect
             // a discriminant property. In cases where the computed type isn't a subset, e.g because of a preceding type
             // predicate narrowing, we use the actual computed type.
             if (declaredType.flags & TypeFlags.Union || computedType.flags & TypeFlags.Union) {
-                const access = getCandidateDiscriminantPropertyAccess(expr);
+                const access = getCandidateDiscriminantPropertyAccess(expr, reference);
                 if (access) {
                     const name = getAccessedPropertyName(access);
                     if (name) {
diff --git a/tests/baselines/reference/typePredicatesCanNarrowByDiscriminant.js b/tests/baselines/reference/typePredicatesCanNarrowByDiscriminant.js
@@ -0,0 +1,30 @@
+//// [tests/cases/compiler/typePredicatesCanNarrowByDiscriminant.ts] ////
+
+//// [typePredicatesCanNarrowByDiscriminant.ts]
+// #45770
+declare const fruit: { kind: 'apple'} | { kind: 'banana' } | { kind: 'cherry' }
+
+declare function isOneOf<T, U extends T>(item: T, array: readonly U[]): item is U
+if (isOneOf(fruit.kind, ['apple', 'banana'] as const)) {
+    fruit.kind
+    fruit
+}
+
+declare const fruit2: { kind: 'apple'} | { kind: 'banana' } | { kind: 'cherry' }
+const kind = fruit2.kind;
+if (isOneOf(kind, ['apple', 'banana'] as const)) {
+    fruit2.kind
+    fruit2
+}
+
+//// [typePredicatesCanNarrowByDiscriminant.js]
+"use strict";
+if (isOneOf(fruit.kind, ['apple', 'banana'])) {
+    fruit.kind;
+    fruit;
+}
+var kind = fruit2.kind;
+if (isOneOf(kind, ['apple', 'banana'])) {
+    fruit2.kind;
+    fruit2;
+}
diff --git a/tests/baselines/reference/typePredicatesCanNarrowByDiscriminant.symbols b/tests/baselines/reference/typePredicatesCanNarrowByDiscriminant.symbols
@@ -0,0 +1,63 @@
+//// [tests/cases/compiler/typePredicatesCanNarrowByDiscriminant.ts] ////
+
+=== typePredicatesCanNarrowByDiscriminant.ts ===
+// #45770
+declare const fruit: { kind: 'apple'} | { kind: 'banana' } | { kind: 'cherry' }
+>fruit : Symbol(fruit, Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 13))
+>kind : Symbol(kind, Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 22))
+>kind : Symbol(kind, Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 41))
+>kind : Symbol(kind, Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 62))
+
+declare function isOneOf<T, U extends T>(item: T, array: readonly U[]): item is U
+>isOneOf : Symbol(isOneOf, Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 79))
+>T : Symbol(T, Decl(typePredicatesCanNarrowByDiscriminant.ts, 3, 25))
+>U : Symbol(U, Decl(typePredicatesCanNarrowByDiscriminant.ts, 3, 27))
+>T : Symbol(T, Decl(typePredicatesCanNarrowByDiscriminant.ts, 3, 25))
+>item : Symbol(item, Decl(typePredicatesCanNarrowByDiscriminant.ts, 3, 41))
+>T : Symbol(T, Decl(typePredicatesCanNarrowByDiscriminant.ts, 3, 25))
+>array : Symbol(array, Decl(typePredicatesCanNarrowByDiscriminant.ts, 3, 49))
+>U : Symbol(U, Decl(typePredicatesCanNarrowByDiscriminant.ts, 3, 27))
+>item : Symbol(item, Decl(typePredicatesCanNarrowByDiscriminant.ts, 3, 41))
+>U : Symbol(U, Decl(typePredicatesCanNarrowByDiscriminant.ts, 3, 27))
+
+if (isOneOf(fruit.kind, ['apple', 'banana'] as const)) {
+>isOneOf : Symbol(isOneOf, Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 79))
+>fruit.kind : Symbol(kind, Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 22), Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 41), Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 62))
+>fruit : Symbol(fruit, Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 13))
+>kind : Symbol(kind, Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 22), Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 41), Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 62))
+>const : Symbol(const)
+
+    fruit.kind
+>fruit.kind : Symbol(kind, Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 22), Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 41))
+>fruit : Symbol(fruit, Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 13))
+>kind : Symbol(kind, Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 22), Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 41))
+
+    fruit
+>fruit : Symbol(fruit, Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 13))
+}
+
+declare const fruit2: { kind: 'apple'} | { kind: 'banana' } | { kind: 'cherry' }
+>fruit2 : Symbol(fruit2, Decl(typePredicatesCanNarrowByDiscriminant.ts, 9, 13))
+>kind : Symbol(kind, Decl(typePredicatesCanNarrowByDiscriminant.ts, 9, 23))
+>kind : Symbol(kind, Decl(typePredicatesCanNarrowByDiscriminant.ts, 9, 42))
+>kind : Symbol(kind, Decl(typePredicatesCanNarrowByDiscriminant.ts, 9, 63))
+
+const kind = fruit2.kind;
+>kind : Symbol(kind, Decl(typePredicatesCanNarrowByDiscriminant.ts, 10, 5))
+>fruit2.kind : Symbol(kind, Decl(typePredicatesCanNarrowByDiscriminant.ts, 9, 23), Decl(typePredicatesCanNarrowByDiscriminant.ts, 9, 42), Decl(typePredicatesCanNarrowByDiscriminant.ts, 9, 63))
+>fruit2 : Symbol(fruit2, Decl(typePredicatesCanNarrowByDiscriminant.ts, 9, 13))
+>kind : Symbol(kind, Decl(typePredicatesCanNarrowByDiscriminant.ts, 9, 23), Decl(typePredicatesCanNarrowByDiscriminant.ts, 9, 42), Decl(typePredicatesCanNarrowByDiscriminant.ts, 9, 63))
+
+if (isOneOf(kind, ['apple', 'banana'] as const)) {
+>isOneOf : Symbol(isOneOf, Decl(typePredicatesCanNarrowByDiscriminant.ts, 1, 79))
+>kind : Symbol(kind, Decl(typePredicatesCanNarrowByDiscriminant.ts, 10, 5))
+>const : Symbol(const)
+
+    fruit2.kind
+>fruit2.kind : Symbol(kind, Decl(typePredicatesCanNarrowByDiscriminant.ts, 9, 23), Decl(typePredicatesCanNarrowByDiscriminant.ts, 9, 42))
+>fruit2 : Symbol(fruit2, Decl(typePredicatesCanNarrowByDiscriminant.ts, 9, 13))
+>kind : Symbol(kind, Decl(typePredicatesCanNarrowByDiscriminant.ts, 9, 23), Decl(typePredicatesCanNarrowByDiscriminant.ts, 9, 42))
+
+    fruit2
+>fruit2 : Symbol(fruit2, Decl(typePredicatesCanNarrowByDiscriminant.ts, 9, 13))
+}
diff --git a/tests/baselines/reference/typePredicatesCanNarrowByDiscriminant.types b/tests/baselines/reference/typePredicatesCanNarrowByDiscriminant.types
@@ -0,0 +1,64 @@
+//// [tests/cases/compiler/typePredicatesCanNarrowByDiscriminant.ts] ////
+
+=== typePredicatesCanNarrowByDiscriminant.ts ===
+// #45770
+declare const fruit: { kind: 'apple'} | { kind: 'banana' } | { kind: 'cherry' }
+>fruit : { kind: 'apple'; } | { kind: 'banana'; } | { kind: 'cherry'; }
+>kind : "apple"
+>kind : "banana"
+>kind : "cherry"
+
+declare function isOneOf<T, U extends T>(item: T, array: readonly U[]): item is U
+>isOneOf : <T, U extends T>(item: T, array: readonly U[]) => item is U
+>item : T
+>array : readonly U[]
+
+if (isOneOf(fruit.kind, ['apple', 'banana'] as const)) {
+>isOneOf(fruit.kind, ['apple', 'banana'] as const) : boolean
+>isOneOf : <T, U extends T>(item: T, array: readonly U[]) => item is U
+>fruit.kind : "apple" | "banana" | "cherry"
+>fruit : { kind: "apple"; } | { kind: "banana"; } | { kind: "cherry"; }
+>kind : "apple" | "banana" | "cherry"
+>['apple', 'banana'] as const : readonly ["apple", "banana"]
+>['apple', 'banana'] : readonly ["apple", "banana"]
+>'apple' : "apple"
+>'banana' : "banana"
+
+    fruit.kind
+>fruit.kind : "apple" | "banana"
+>fruit : { kind: "apple"; } | { kind: "banana"; }
+>kind : "apple" | "banana"
+
+    fruit
+>fruit : { kind: "apple"; } | { kind: "banana"; }
+}
+
+declare const fruit2: { kind: 'apple'} | { kind: 'banana' } | { kind: 'cherry' }
+>fruit2 : { kind: 'apple'; } | { kind: 'banana'; } | { kind: 'cherry'; }
+>kind : "apple"
+>kind : "banana"
+>kind : "cherry"
+
+const kind = fruit2.kind;
+>kind : "apple" | "banana" | "cherry"
+>fruit2.kind : "apple" | "banana" | "cherry"
+>fruit2 : { kind: "apple"; } | { kind: "banana"; } | { kind: "cherry"; }
+>kind : "apple" | "banana" | "cherry"
+
+if (isOneOf(kind, ['apple', 'banana'] as const)) {
+>isOneOf(kind, ['apple', 'banana'] as const) : boolean
+>isOneOf : <T, U extends T>(item: T, array: readonly U[]) => item is U
+>kind : "apple" | "banana" | "cherry"
+>['apple', 'banana'] as const : readonly ["apple", "banana"]
+>['apple', 'banana'] : readonly ["apple", "banana"]
+>'apple' : "apple"
+>'banana' : "banana"
+
+    fruit2.kind
+>fruit2.kind : "apple" | "banana"
+>fruit2 : { kind: "apple"; } | { kind: "banana"; }
+>kind : "apple" | "banana"
+
+    fruit2
+>fruit2 : { kind: "apple"; } | { kind: "banana"; }
+}
diff --git a/tests/cases/compiler/typePredicatesCanNarrowByDiscriminant.ts b/tests/cases/compiler/typePredicatesCanNarrowByDiscriminant.ts
@@ -0,0 +1,17 @@
+// @strict: true
+
+// #45770
+declare const fruit: { kind: 'apple'} | { kind: 'banana' } | { kind: 'cherry' }
+
+declare function isOneOf<T, U extends T>(item: T, array: readonly U[]): item is U
+if (isOneOf(fruit.kind, ['apple', 'banana'] as const)) {
+    fruit.kind
+    fruit
+}
+
+declare const fruit2: { kind: 'apple'} | { kind: 'banana' } | { kind: 'cherry' }
+const kind = fruit2.kind;
+if (isOneOf(kind, ['apple', 'banana'] as const)) {
+    fruit2.kind
+    fruit2
+}
