Fix destructuring and narrowing interaction

src/harness/fourslashImpl.ts

@@ -1120,6 +1120,17 @@ namespace FourSlash {
             }
         }
 
+        public verifyTypeAtLocation(range: Range, expected: string): void {
+            const checker = this.getChecker();
+            const node = this.goToAndGetNode(range);
+            const type = checker.getTypeAtLocation(node);
+
+            const actual = checker.typeToString(type);
+            if (actual !== expected) {
+                this.raiseError(displayExpectedAndActualString(expected, actual));
+            }
+        }
+
         private verifyDocumentHighlightsRespectFilesList(files: readonly string[]): void {
             const startFile = this.activeFile.fileName;
             for (const fileName of files) {

src/harness/fourslashInterfaceImpl.ts

@@ -348,6 +348,10 @@ namespace FourSlashInterface {
             this.state.verifyTypeOfSymbolAtLocation(range, symbol, expected);
         }
 
+        public typeAtLocation(range: FourSlash.Range, expected: string): void {
+            this.state.verifyTypeAtLocation(range, expected);
+        }
+
         public baselineFindAllReferences(...markerNames: string[]) {
             this.state.verifyBaselineFindAllReferences(...markerNames);
         }

tests/baselines/reference/genericObjectSpreadResultInSwitch.types

@@ -25,7 +25,7 @@ const getType = <P extends Params>(params: P) => {
 >rest : Omit<P, "foo">
 
     } = params;
->params : P
+>params : Params
 
     return rest;
 >rest : Omit<P, "foo">

tests/baselines/reference/narrowingDestructuring.js

@@ -0,0 +1,89 @@
+//// [narrowingDestructuring.ts]
+type X = { kind: "a", a: string } | { kind: "b", b: string }
+
+function func<T extends X>(value: T) {
+    if (value.kind === "a") {
+        value.a;
+        const { a } = value;
+    } else {
+        value.b;
+        const { b } = value;
+    }
+}
+
+type Z = { kind: "f", f: { a: number, b: string, c: number } }
+    | { kind: "g", g: { a: string, b: number, c: string }};
+
+function func2<T extends Z>(value: T) {
+    if (value.kind === "f") {
+        const { f: f1 } = value;
+        const { f: { a, ...spread } } = value;
+        value.f;
+    } else {
+        const { g: { c, ...spread } } = value;
+        value.g;
+    }
+}
+
+function func3<T extends { kind: "a", a: string } | { kind: "b", b: number }>(t: T) {
+    if (t.kind === "a") {
+        const { kind, ...r1 } = t;
+        const r2 = (({ kind, ...rest }) => rest)(t);
+    }
+}
+
+function farr<T extends [number, string, string] | [string, number, number]>(x: T) {
+    const [head, ...tail] = x;
+    if (x[0] === 'number') {
+        const [head, ...tail] = x;
+    }
+}
+
+//// [narrowingDestructuring.js]
+var __rest = (this && this.__rest) || function (s, e) {
+    var t = {};
+    for (var p in s) if (Object.prototype.hasOwnProperty.call(s, p) && e.indexOf(p) < 0)
+        t[p] = s[p];
+    if (s != null && typeof Object.getOwnPropertySymbols === "function")
+        for (var i = 0, p = Object.getOwnPropertySymbols(s); i < p.length; i++) {
+            if (e.indexOf(p[i]) < 0 && Object.prototype.propertyIsEnumerable.call(s, p[i]))
+                t[p[i]] = s[p[i]];
+        }
+    return t;
+};
+function func(value) {
+    if (value.kind === "a") {
+        value.a;
+        var a = value.a;
+    }
+    else {
+        value.b;
+        var b = value.b;
+    }
+}
+function func2(value) {
+    if (value.kind === "f") {
+        var f1 = value.f;
+        var _a = value.f, a = _a.a, spread = __rest(_a, ["a"]);
+        value.f;
+    }
+    else {
+        var _b = value.g, c = _b.c, spread = __rest(_b, ["c"]);
+        value.g;
+    }
+}
+function func3(t) {
+    if (t.kind === "a") {
+        var kind = t.kind, r1 = __rest(t, ["kind"]);
+        var r2 = (function (_a) {
+            var kind = _a.kind, rest = __rest(_a, ["kind"]);
+            return rest;
+        })(t);
+    }
+}
+function farr(x) {
+    var head = x[0], tail = x.slice(1);
+    if (x[0] === 'number') {
+        var head_1 = x[0], tail_1 = x.slice(1);
+    }
+}

tests/baselines/reference/narrowingDestructuring.symbols

@@ -0,0 +1,148 @@
+=== tests/cases/compiler/narrowingDestructuring.ts ===
+type X = { kind: "a", a: string } | { kind: "b", b: string }
+>X : Symbol(X, Decl(narrowingDestructuring.ts, 0, 0))
+>kind : Symbol(kind, Decl(narrowingDestructuring.ts, 0, 10))
+>a : Symbol(a, Decl(narrowingDestructuring.ts, 0, 21))
+>kind : Symbol(kind, Decl(narrowingDestructuring.ts, 0, 37))
+>b : Symbol(b, Decl(narrowingDestructuring.ts, 0, 48))
+
+function func<T extends X>(value: T) {
+>func : Symbol(func, Decl(narrowingDestructuring.ts, 0, 60))
+>T : Symbol(T, Decl(narrowingDestructuring.ts, 2, 14))
+>X : Symbol(X, Decl(narrowingDestructuring.ts, 0, 0))
+>value : Symbol(value, Decl(narrowingDestructuring.ts, 2, 27))
+>T : Symbol(T, Decl(narrowingDestructuring.ts, 2, 14))
+
+    if (value.kind === "a") {
+>value.kind : Symbol(kind, Decl(narrowingDestructuring.ts, 0, 10), Decl(narrowingDestructuring.ts, 0, 37))
+>value : Symbol(value, Decl(narrowingDestructuring.ts, 2, 27))
+>kind : Symbol(kind, Decl(narrowingDestructuring.ts, 0, 10), Decl(narrowingDestructuring.ts, 0, 37))
+
+        value.a;
+>value.a : Symbol(a, Decl(narrowingDestructuring.ts, 0, 21))
+>value : Symbol(value, Decl(narrowingDestructuring.ts, 2, 27))
+>a : Symbol(a, Decl(narrowingDestructuring.ts, 0, 21))
+
+        const { a } = value;
+>a : Symbol(a, Decl(narrowingDestructuring.ts, 5, 15))
+>value : Symbol(value, Decl(narrowingDestructuring.ts, 2, 27))
+
+    } else {
+        value.b;
+>value.b : Symbol(b, Decl(narrowingDestructuring.ts, 0, 48))
+>value : Symbol(value, Decl(narrowingDestructuring.ts, 2, 27))
+>b : Symbol(b, Decl(narrowingDestructuring.ts, 0, 48))
+
+        const { b } = value;
+>b : Symbol(b, Decl(narrowingDestructuring.ts, 8, 15))
+>value : Symbol(value, Decl(narrowingDestructuring.ts, 2, 27))
+    }
+}
+
+type Z = { kind: "f", f: { a: number, b: string, c: number } }
+>Z : Symbol(Z, Decl(narrowingDestructuring.ts, 10, 1))
+>kind : Symbol(kind, Decl(narrowingDestructuring.ts, 12, 10))
+>f : Symbol(f, Decl(narrowingDestructuring.ts, 12, 21))
+>a : Symbol(a, Decl(narrowingDestructuring.ts, 12, 26))
+>b : Symbol(b, Decl(narrowingDestructuring.ts, 12, 37))
+>c : Symbol(c, Decl(narrowingDestructuring.ts, 12, 48))
+
+    | { kind: "g", g: { a: string, b: number, c: string }};
+>kind : Symbol(kind, Decl(narrowingDestructuring.ts, 13, 7))
+>g : Symbol(g, Decl(narrowingDestructuring.ts, 13, 18))
+>a : Symbol(a, Decl(narrowingDestructuring.ts, 13, 23))
+>b : Symbol(b, Decl(narrowingDestructuring.ts, 13, 34))
+>c : Symbol(c, Decl(narrowingDestructuring.ts, 13, 45))
+
+function func2<T extends Z>(value: T) {
+>func2 : Symbol(func2, Decl(narrowingDestructuring.ts, 13, 59))
+>T : Symbol(T, Decl(narrowingDestructuring.ts, 15, 15))
+>Z : Symbol(Z, Decl(narrowingDestructuring.ts, 10, 1))
+>value : Symbol(value, Decl(narrowingDestructuring.ts, 15, 28))
+>T : Symbol(T, Decl(narrowingDestructuring.ts, 15, 15))
+
+    if (value.kind === "f") {
+>value.kind : Symbol(kind, Decl(narrowingDestructuring.ts, 12, 10), Decl(narrowingDestructuring.ts, 13, 7))
+>value : Symbol(value, Decl(narrowingDestructuring.ts, 15, 28))
+>kind : Symbol(kind, Decl(narrowingDestructuring.ts, 12, 10), Decl(narrowingDestructuring.ts, 13, 7))
+
+        const { f: f1 } = value;
+>f : Symbol(f, Decl(narrowingDestructuring.ts, 12, 21))
+>f1 : Symbol(f1, Decl(narrowingDestructuring.ts, 17, 15))
+>value : Symbol(value, Decl(narrowingDestructuring.ts, 15, 28))
+
+        const { f: { a, ...spread } } = value;
+>f : Symbol(f, Decl(narrowingDestructuring.ts, 12, 21))
+>a : Symbol(a, Decl(narrowingDestructuring.ts, 18, 20))
+>spread : Symbol(spread, Decl(narrowingDestructuring.ts, 18, 23))
+>value : Symbol(value, Decl(narrowingDestructuring.ts, 15, 28))
+
+        value.f;
+>value.f : Symbol(f, Decl(narrowingDestructuring.ts, 12, 21))
+>value : Symbol(value, Decl(narrowingDestructuring.ts, 15, 28))
+>f : Symbol(f, Decl(narrowingDestructuring.ts, 12, 21))
+
+    } else {
+        const { g: { c, ...spread } } = value;
+>g : Symbol(g, Decl(narrowingDestructuring.ts, 13, 18))
+>c : Symbol(c, Decl(narrowingDestructuring.ts, 21, 20))
+>spread : Symbol(spread, Decl(narrowingDestructuring.ts, 21, 23))
+>value : Symbol(value, Decl(narrowingDestructuring.ts, 15, 28))
+
+        value.g;
+>value.g : Symbol(g, Decl(narrowingDestructuring.ts, 13, 18))
+>value : Symbol(value, Decl(narrowingDestructuring.ts, 15, 28))
+>g : Symbol(g, Decl(narrowingDestructuring.ts, 13, 18))
+    }
+}
+
+function func3<T extends { kind: "a", a: string } | { kind: "b", b: number }>(t: T) {
+>func3 : Symbol(func3, Decl(narrowingDestructuring.ts, 24, 1))
+>T : Symbol(T, Decl(narrowingDestructuring.ts, 26, 15))
+>kind : Symbol(kind, Decl(narrowingDestructuring.ts, 26, 26))
+>a : Symbol(a, Decl(narrowingDestructuring.ts, 26, 37))
+>kind : Symbol(kind, Decl(narrowingDestructuring.ts, 26, 53))
+>b : Symbol(b, Decl(narrowingDestructuring.ts, 26, 64))
+>t : Symbol(t, Decl(narrowingDestructuring.ts, 26, 78))
+>T : Symbol(T, Decl(narrowingDestructuring.ts, 26, 15))
+
+    if (t.kind === "a") {
+>t.kind : Symbol(kind, Decl(narrowingDestructuring.ts, 26, 26), Decl(narrowingDestructuring.ts, 26, 53))
+>t : Symbol(t, Decl(narrowingDestructuring.ts, 26, 78))
+>kind : Symbol(kind, Decl(narrowingDestructuring.ts, 26, 26), Decl(narrowingDestructuring.ts, 26, 53))
+
+        const { kind, ...r1 } = t;
+>kind : Symbol(kind, Decl(narrowingDestructuring.ts, 28, 15))
+>r1 : Symbol(r1, Decl(narrowingDestructuring.ts, 28, 21))
+>t : Symbol(t, Decl(narrowingDestructuring.ts, 26, 78))
+
+        const r2 = (({ kind, ...rest }) => rest)(t);
+>r2 : Symbol(r2, Decl(narrowingDestructuring.ts, 29, 13))
+>kind : Symbol(kind, Decl(narrowingDestructuring.ts, 29, 22))
+>rest : Symbol(rest, Decl(narrowingDestructuring.ts, 29, 28))
+>rest : Symbol(rest, Decl(narrowingDestructuring.ts, 29, 28))
+>t : Symbol(t, Decl(narrowingDestructuring.ts, 26, 78))
+    }
+}
+
+function farr<T extends [number, string, string] | [string, number, number]>(x: T) {
+>farr : Symbol(farr, Decl(narrowingDestructuring.ts, 31, 1))
+>T : Symbol(T, Decl(narrowingDestructuring.ts, 33, 14))
+>x : Symbol(x, Decl(narrowingDestructuring.ts, 33, 77))
+>T : Symbol(T, Decl(narrowingDestructuring.ts, 33, 14))
+
+    const [head, ...tail] = x;
+>head : Symbol(head, Decl(narrowingDestructuring.ts, 34, 11))
+>tail : Symbol(tail, Decl(narrowingDestructuring.ts, 34, 16))
+>x : Symbol(x, Decl(narrowingDestructuring.ts, 33, 77))
+
+    if (x[0] === 'number') {
+>x : Symbol(x, Decl(narrowingDestructuring.ts, 33, 77))
+>0 : Symbol(0)
+
+        const [head, ...tail] = x;
+>head : Symbol(head, Decl(narrowingDestructuring.ts, 36, 15))
+>tail : Symbol(tail, Decl(narrowingDestructuring.ts, 36, 20))
+>x : Symbol(x, Decl(narrowingDestructuring.ts, 33, 77))
+    }
+}