Fix narrowing of destructured discriminated union parameters with defaults

src/compiler/checker.ts

@@ -29475,7 +29475,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 if (isIdentifier(expr)) {
                     const symbol = getResolvedSymbol(expr);
                     const declaration = getExportSymbolOfValueSymbolIfExported(symbol).valueDeclaration;
-                    if (declaration && (isBindingElement(declaration) || isParameter(declaration)) && reference === declaration.parent && !declaration.initializer && !declaration.dotDotDotToken) {
+                    if (declaration && (isBindingElement(declaration) || isParameter(declaration)) && reference === declaration.parent && !declaration.dotDotDotToken) {
                         return declaration;
                     }
                 }
@@ -30947,7 +30947,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             // the binding pattern AST instance for '{ kind, payload }' as a pseudo-reference and narrow this reference
             // as if it occurred in the specified location. We then recompute the narrowed binding element type by
             // destructuring from the narrowed parent type.
-            if (isBindingElement(declaration) && !declaration.initializer && !declaration.dotDotDotToken && declaration.parent.elements.length >= 2) {
+            if (isBindingElement(declaration) && !declaration.dotDotDotToken && declaration.parent.elements.length >= 2) {
                 const parent = declaration.parent.parent;
                 const rootDeclaration = getRootDeclaration(parent);
                 if (rootDeclaration.kind === SyntaxKind.VariableDeclaration && getCombinedNodeFlagsCached(rootDeclaration) & NodeFlags.Constant || rootDeclaration.kind === SyntaxKind.Parameter) {

tests/baselines/reference/discriminatedUnionDestructuringWithDefaults.errors.txt

@@ -0,0 +1,40 @@
+discriminatedUnionDestructuringWithDefaults.ts(26,43): error TS2322: Type 'boolean' is not assignable to type 'string | number'.
+
+
+==== discriminatedUnionDestructuringWithDefaults.ts (1 errors) ====
+    // Case 1: the issue #50139 repro — must compile clean after the fix
+    function repro({ isText = false, children = 0 }:
+        { isText: true; children?: string }
+      | { isText: false; children?: number }
+    ) {
+        if (isText === true) {
+            let data: string = children;
+        } else if (isText === false) {
+            let data: number = children;
+        }
+    }
+
+    // Case 2: control — no defaults, already worked, must not regress
+    function control({ isText, children }:
+        { isText: true; children: string }
+      | { isText: false; children: number }
+    ) {
+        if (isText === true) {
+            let data: string = children;
+        } else if (isText === false) {
+            let data: number = children;
+        }
+    }
+
+    // Case 3: whzx5byb's soundness check — default foreign to one arm must still error
+    function soundnessCheck({ isText = false, children = true }: // expect error on `children = true`
+                                              ~~~~~~~~
+!!! error TS2322: Type 'boolean' is not assignable to type 'string | number'.
+        { isText: true; children?: string }
+      | { isText: false; children?: number }
+    ) {
+        if (isText === true) {
+            let data: string = children;
+        }
+    }
+

tests/baselines/reference/discriminatedUnionDestructuringWithDefaults.js

@@ -0,0 +1,64 @@
+//// [tests/cases/compiler/discriminatedUnionDestructuringWithDefaults.ts] ////
+
+//// [discriminatedUnionDestructuringWithDefaults.ts]
+// Case 1: the issue #50139 repro — must compile clean after the fix
+function repro({ isText = false, children = 0 }:
+    { isText: true; children?: string }
+  | { isText: false; children?: number }
+) {
+    if (isText === true) {
+        let data: string = children;
+    } else if (isText === false) {
+        let data: number = children;
+    }
+}
+
+// Case 2: control — no defaults, already worked, must not regress
+function control({ isText, children }:
+    { isText: true; children: string }
+  | { isText: false; children: number }
+) {
+    if (isText === true) {
+        let data: string = children;
+    } else if (isText === false) {
+        let data: number = children;
+    }
+}
+
+// Case 3: whzx5byb's soundness check — default foreign to one arm must still error
+function soundnessCheck({ isText = false, children = true }: // expect error on `children = true`
+    { isText: true; children?: string }
+  | { isText: false; children?: number }
+) {
+    if (isText === true) {
+        let data: string = children;
+    }
+}
+
+
+//// [discriminatedUnionDestructuringWithDefaults.js]
+"use strict";
+// Case 1: the issue #50139 repro — must compile clean after the fix
+function repro({ isText = false, children = 0 }) {
+    if (isText === true) {
+        let data = children;
+    }
+    else if (isText === false) {
+        let data = children;
+    }
+}
+// Case 2: control — no defaults, already worked, must not regress
+function control({ isText, children }) {
+    if (isText === true) {
+        let data = children;
+    }
+    else if (isText === false) {
+        let data = children;
+    }
+}
+// Case 3: whzx5byb's soundness check — default foreign to one arm must still error
+function soundnessCheck({ isText = false, children = true }) {
+    if (isText === true) {
+        let data = children;
+    }
+}

tests/baselines/reference/discriminatedUnionDestructuringWithDefaults.symbols

@@ -0,0 +1,89 @@
+//// [tests/cases/compiler/discriminatedUnionDestructuringWithDefaults.ts] ////
+
+=== discriminatedUnionDestructuringWithDefaults.ts ===
+// Case 1: the issue #50139 repro — must compile clean after the fix
+function repro({ isText = false, children = 0 }:
+>repro : Symbol(repro, Decl(discriminatedUnionDestructuringWithDefaults.ts, 0, 0))
+>isText : Symbol(isText, Decl(discriminatedUnionDestructuringWithDefaults.ts, 1, 16))
+>children : Symbol(children, Decl(discriminatedUnionDestructuringWithDefaults.ts, 1, 32))
+
+    { isText: true; children?: string }
+>isText : Symbol(isText, Decl(discriminatedUnionDestructuringWithDefaults.ts, 2, 5))
+>children : Symbol(children, Decl(discriminatedUnionDestructuringWithDefaults.ts, 2, 19))
+
+  | { isText: false; children?: number }
+>isText : Symbol(isText, Decl(discriminatedUnionDestructuringWithDefaults.ts, 3, 5))
+>children : Symbol(children, Decl(discriminatedUnionDestructuringWithDefaults.ts, 3, 20))
+
+) {
+    if (isText === true) {
+>isText : Symbol(isText, Decl(discriminatedUnionDestructuringWithDefaults.ts, 1, 16))
+
+        let data: string = children;
+>data : Symbol(data, Decl(discriminatedUnionDestructuringWithDefaults.ts, 6, 11))
+>children : Symbol(children, Decl(discriminatedUnionDestructuringWithDefaults.ts, 1, 32))
+
+    } else if (isText === false) {
+>isText : Symbol(isText, Decl(discriminatedUnionDestructuringWithDefaults.ts, 1, 16))
+
+        let data: number = children;
+>data : Symbol(data, Decl(discriminatedUnionDestructuringWithDefaults.ts, 8, 11))
+>children : Symbol(children, Decl(discriminatedUnionDestructuringWithDefaults.ts, 1, 32))
+    }
+}
+
+// Case 2: control — no defaults, already worked, must not regress
+function control({ isText, children }:
+>control : Symbol(control, Decl(discriminatedUnionDestructuringWithDefaults.ts, 10, 1))
+>isText : Symbol(isText, Decl(discriminatedUnionDestructuringWithDefaults.ts, 13, 18))
+>children : Symbol(children, Decl(discriminatedUnionDestructuringWithDefaults.ts, 13, 26))
+
+    { isText: true; children: string }
+>isText : Symbol(isText, Decl(discriminatedUnionDestructuringWithDefaults.ts, 14, 5))
+>children : Symbol(children, Decl(discriminatedUnionDestructuringWithDefaults.ts, 14, 19))
+
+  | { isText: false; children: number }
+>isText : Symbol(isText, Decl(discriminatedUnionDestructuringWithDefaults.ts, 15, 5))
+>children : Symbol(children, Decl(discriminatedUnionDestructuringWithDefaults.ts, 15, 20))
+
+) {
+    if (isText === true) {
+>isText : Symbol(isText, Decl(discriminatedUnionDestructuringWithDefaults.ts, 13, 18))
+
+        let data: string = children;
+>data : Symbol(data, Decl(discriminatedUnionDestructuringWithDefaults.ts, 18, 11))
+>children : Symbol(children, Decl(discriminatedUnionDestructuringWithDefaults.ts, 13, 26))
+
+    } else if (isText === false) {
+>isText : Symbol(isText, Decl(discriminatedUnionDestructuringWithDefaults.ts, 13, 18))
+
+        let data: number = children;
+>data : Symbol(data, Decl(discriminatedUnionDestructuringWithDefaults.ts, 20, 11))
+>children : Symbol(children, Decl(discriminatedUnionDestructuringWithDefaults.ts, 13, 26))
+    }
+}
+
+// Case 3: whzx5byb's soundness check — default foreign to one arm must still error
+function soundnessCheck({ isText = false, children = true }: // expect error on `children = true`
+>soundnessCheck : Symbol(soundnessCheck, Decl(discriminatedUnionDestructuringWithDefaults.ts, 22, 1))
+>isText : Symbol(isText, Decl(discriminatedUnionDestructuringWithDefaults.ts, 25, 25))
+>children : Symbol(children, Decl(discriminatedUnionDestructuringWithDefaults.ts, 25, 41))
+
+    { isText: true; children?: string }
+>isText : Symbol(isText, Decl(discriminatedUnionDestructuringWithDefaults.ts, 26, 5))
+>children : Symbol(children, Decl(discriminatedUnionDestructuringWithDefaults.ts, 26, 19))
+
+  | { isText: false; children?: number }
+>isText : Symbol(isText, Decl(discriminatedUnionDestructuringWithDefaults.ts, 27, 5))
+>children : Symbol(children, Decl(discriminatedUnionDestructuringWithDefaults.ts, 27, 20))
+
+) {
+    if (isText === true) {
+>isText : Symbol(isText, Decl(discriminatedUnionDestructuringWithDefaults.ts, 25, 25))
+
+        let data: string = children;
+>data : Symbol(data, Decl(discriminatedUnionDestructuringWithDefaults.ts, 30, 11))
+>children : Symbol(children, Decl(discriminatedUnionDestructuringWithDefaults.ts, 25, 41))
+    }
+}
+

tests/baselines/reference/discriminatedUnionDestructuringWithDefaults.types

@@ -0,0 +1,165 @@
+//// [tests/cases/compiler/discriminatedUnionDestructuringWithDefaults.ts] ////
+
+=== discriminatedUnionDestructuringWithDefaults.ts ===
+// Case 1: the issue #50139 repro — must compile clean after the fix
+function repro({ isText = false, children = 0 }:
+>repro : ({ isText, children }: { isText: true; children?: string; } | { isText: false; children?: number; }) => void
+>      : ^                    ^^                                                                            ^^^^^^^^^
+>isText : boolean
+>       : ^^^^^^^
+>false : false
+>      : ^^^^^
+>children : string | number
+>         : ^^^^^^^^^^^^^^^
+>0 : 0
+>  : ^
+
+    { isText: true; children?: string }
+>isText : true
+>       : ^^^^
+>true : true
+>     : ^^^^
+>children : string | undefined
+>         : ^^^^^^^^^^^^^^^^^^
+
+  | { isText: false; children?: number }
+>isText : false
+>       : ^^^^^
+>false : false
+>      : ^^^^^
+>children : number | undefined
+>         : ^^^^^^^^^^^^^^^^^^
+
+) {
+    if (isText === true) {
+>isText === true : boolean
+>                : ^^^^^^^
+>isText : boolean
+>       : ^^^^^^^
+>true : true
+>     : ^^^^
+
+        let data: string = children;
+>data : string
+>     : ^^^^^^
+>children : string
+>         : ^^^^^^
+
+    } else if (isText === false) {
+>isText === false : boolean
+>                 : ^^^^^^^
+>isText : false
+>       : ^^^^^
+>false : false
+>      : ^^^^^
+
+        let data: number = children;
+>data : number
+>     : ^^^^^^
+>children : number
+>         : ^^^^^^
+    }
+}
+
+// Case 2: control — no defaults, already worked, must not regress
+function control({ isText, children }:
+>control : ({ isText, children }: { isText: true; children: string; } | { isText: false; children: number; }) => void
+>        : ^                    ^^                                                                          ^^^^^^^^^
+>isText : boolean
+>       : ^^^^^^^
+>children : string | number
+>         : ^^^^^^^^^^^^^^^
+
+    { isText: true; children: string }
+>isText : true
+>       : ^^^^
+>true : true
+>     : ^^^^
+>children : string
+>         : ^^^^^^
+
+  | { isText: false; children: number }
+>isText : false
+>       : ^^^^^
+>false : false
+>      : ^^^^^
+>children : number
+>         : ^^^^^^
+
+) {
+    if (isText === true) {
+>isText === true : boolean
+>                : ^^^^^^^
+>isText : boolean
+>       : ^^^^^^^
+>true : true
+>     : ^^^^
+
+        let data: string = children;
+>data : string
+>     : ^^^^^^
+>children : string
+>         : ^^^^^^
+
+    } else if (isText === false) {
+>isText === false : boolean
+>                 : ^^^^^^^
+>isText : false
+>       : ^^^^^
+>false : false
+>      : ^^^^^
+
+        let data: number = children;
+>data : number
+>     : ^^^^^^
+>children : number
+>         : ^^^^^^
+    }
+}
+
+// Case 3: whzx5byb's soundness check — default foreign to one arm must still error
+function soundnessCheck({ isText = false, children = true }: // expect error on `children = true`
+>soundnessCheck : ({ isText, children }: { isText: true; children?: string; } | { isText: false; children?: number; }) => void
+>               : ^                    ^^                                                                            ^^^^^^^^^
+>isText : boolean
+>       : ^^^^^^^
+>false : false
+>      : ^^^^^
+>children : string | number
+>         : ^^^^^^^^^^^^^^^
+>true : true
+>     : ^^^^
+
+    { isText: true; children?: string }
+>isText : true
+>       : ^^^^
+>true : true
+>     : ^^^^
+>children : string | undefined
+>         : ^^^^^^^^^^^^^^^^^^
+
+  | { isText: false; children?: number }
+>isText : false
+>       : ^^^^^
+>false : false
+>      : ^^^^^
+>children : number | undefined
+>         : ^^^^^^^^^^^^^^^^^^
+
+) {
+    if (isText === true) {
+>isText === true : boolean
+>                : ^^^^^^^
+>isText : boolean
+>       : ^^^^^^^
+>true : true
+>     : ^^^^
+
+        let data: string = children;
+>data : string
+>     : ^^^^^^
+>children : string
+>         : ^^^^^^
+    }
+}
+