CFA for dependent parameters typed by generic constraints (microsoft#48411)

* Obtain apparent type in parameter destructuring check

* Add regression test

Author: ahejlsberg

src/compiler/checker.ts

@@ -25450,7 +25450,7 @@ namespace ts {
                     if (func.parameters.length >= 2 && isContextSensitiveFunctionOrObjectLiteralMethod(func)) {
                         const contextualSignature = getContextualSignature(func);
                         if (contextualSignature && contextualSignature.parameters.length === 1 && signatureHasRestParameter(contextualSignature)) {
-                            const restType = getTypeOfSymbol(contextualSignature.parameters[0]);
+                            const restType = getReducedApparentType(getTypeOfSymbol(contextualSignature.parameters[0]));
                             if (restType.flags & TypeFlags.Union && everyType(restType, isTupleType) && !isSymbolAssigned(symbol)) {
                                 const narrowedType = getFlowTypeOfReference(func, restType, restType, /*flowContainer*/ undefined, location.flowNode);
                                 const index = func.parameters.indexOf(declaration) - (getThisParameter(func) ? 1 : 0);

tests/baselines/reference/dependentDestructuredVariables.js

@@ -295,6 +295,19 @@ let fooAsyncGenM: FooAsyncGenMethod = {
     }
   }
 };
+
+// Repro from #48345
+
+type Func = <T extends ["a", number] | ["b", string]>(...args: T) => void;
+
+const f60: Func = (kind, payload) => {
+    if (kind === "a") {
+        payload.toFixed();  // error
+    }
+    if (kind === "b") {
+        payload.toUpperCase();  // error
+    }
+};
 
 
 //// [dependentDestructuredVariables.js]
@@ -529,6 +542,14 @@ let fooAsyncGenM = {
         });
     }
 };
+const f60 = (kind, payload) => {
+    if (kind === "a") {
+        payload.toFixed(); // error
+    }
+    if (kind === "b") {
+        payload.toUpperCase(); // error
+    }
+};
 
 
 //// [dependentDestructuredVariables.d.ts]
@@ -644,3 +665,5 @@ declare type FooAsyncGenMethod = {
     ]): AsyncGenerator<any, any, any>;
 };
 declare let fooAsyncGenM: FooAsyncGenMethod;
+declare type Func = <T extends ["a", number] | ["b", string]>(...args: T) => void;
+declare const f60: Func;

tests/baselines/reference/dependentDestructuredVariables.symbols

@@ -752,3 +752,35 @@ let fooAsyncGenM: FooAsyncGenMethod = {
   }
 };
 
+// Repro from #48345
+
+type Func = <T extends ["a", number] | ["b", string]>(...args: T) => void;
+>Func : Symbol(Func, Decl(dependentDestructuredVariables.ts, 295, 2))
+>T : Symbol(T, Decl(dependentDestructuredVariables.ts, 299, 13))
+>args : Symbol(args, Decl(dependentDestructuredVariables.ts, 299, 54))
+>T : Symbol(T, Decl(dependentDestructuredVariables.ts, 299, 13))
+
+const f60: Func = (kind, payload) => {
+>f60 : Symbol(f60, Decl(dependentDestructuredVariables.ts, 301, 5))
+>Func : Symbol(Func, Decl(dependentDestructuredVariables.ts, 295, 2))
+>kind : Symbol(kind, Decl(dependentDestructuredVariables.ts, 301, 19))
+>payload : Symbol(payload, Decl(dependentDestructuredVariables.ts, 301, 24))
+
+    if (kind === "a") {
+>kind : Symbol(kind, Decl(dependentDestructuredVariables.ts, 301, 19))
+
+        payload.toFixed();  // error
+>payload.toFixed : Symbol(Number.toFixed, Decl(lib.es5.d.ts, --, --))
+>payload : Symbol(payload, Decl(dependentDestructuredVariables.ts, 301, 24))
+>toFixed : Symbol(Number.toFixed, Decl(lib.es5.d.ts, --, --))
+    }
+    if (kind === "b") {
+>kind : Symbol(kind, Decl(dependentDestructuredVariables.ts, 301, 19))
+
+        payload.toUpperCase();  // error
+>payload.toUpperCase : Symbol(String.toUpperCase, Decl(lib.es5.d.ts, --, --))
+>payload : Symbol(payload, Decl(dependentDestructuredVariables.ts, 301, 24))
+>toUpperCase : Symbol(String.toUpperCase, Decl(lib.es5.d.ts, --, --))
+    }
+};
+

tests/baselines/reference/dependentDestructuredVariables.types

@@ -855,3 +855,39 @@ let fooAsyncGenM: FooAsyncGenMethod = {
   }
 };
 
+// Repro from #48345
+
+type Func = <T extends ["a", number] | ["b", string]>(...args: T) => void;
+>Func : Func
+>args : T
+
+const f60: Func = (kind, payload) => {
+>f60 : Func
+>(kind, payload) => {    if (kind === "a") {        payload.toFixed();  // error    }    if (kind === "b") {        payload.toUpperCase();  // error    }} : <T extends ["a", number] | ["b", string]>(kind: T[0], payload: T[1]) => void
+>kind : T[0]
+>payload : T[1]
+
+    if (kind === "a") {
+>kind === "a" : boolean
+>kind : "a" | "b"
+>"a" : "a"
+
+        payload.toFixed();  // error
+>payload.toFixed() : string
+>payload.toFixed : (fractionDigits?: number | undefined) => string
+>payload : number
+>toFixed : (fractionDigits?: number | undefined) => string
+    }
+    if (kind === "b") {
+>kind === "b" : boolean
+>kind : "a" | "b"
+>"b" : "b"
+
+        payload.toUpperCase();  // error
+>payload.toUpperCase() : string
+>payload.toUpperCase : () => string
+>payload : string
+>toUpperCase : () => string
+    }
+};
+

tests/cases/conformance/controlFlow/dependentDestructuredVariables.ts

@@ -299,3 +299,16 @@ let fooAsyncGenM: FooAsyncGenMethod = {
     }
   }
 };
+
+// Repro from #48345
+
+type Func = <T extends ["a", number] | ["b", string]>(...args: T) => void;
+
+const f60: Func = (kind, payload) => {
+    if (kind === "a") {
+        payload.toFixed();  // error
+    }
+    if (kind === "b") {
+        payload.toUpperCase();  // error
+    }
+};