Support properties of mapped types in assertion control flow analysis (#40482)

* Support properties of mapped types in assertion control flow analysis

* Add regression test

* Accept new baselines

Author: ahejlsberg

src/compiler/checker.ts

@@ -21103,6 +21103,12 @@ namespace ts {
                 return getTypeOfSymbol(symbol);
             }
             if (symbol.flags & (SymbolFlags.Variable | SymbolFlags.Property)) {
+                if (getCheckFlags(symbol) & CheckFlags.Mapped) {
+                    const origin = (<MappedSymbol>symbol).syntheticOrigin;
+                    if (origin && getExplicitTypeOfSymbol(origin)) {
+                        return getTypeOfSymbol(symbol);
+                    }
+                }
                 const declaration = symbol.valueDeclaration;
                 if (declaration) {
                     if (isDeclarationWithExplicitTypeAnnotation(declaration)) {

tests/baselines/reference/neverReturningFunctions1.errors.txt

@@ -318,4 +318,18 @@ tests/cases/conformance/controlFlow/neverReturningFunctions1.ts(153,5): error TS
             this.throw()
         }
     }
+    
+    // Repro from #40346
+    
+    interface Services {
+        panic(message: string): never;
+    }
+    
+    function foo(services: Readonly<Services>, s: string | null): string {
+        if (s === null) {
+            services.panic("ouch");
+        } else {
+            return s;
+        }
+    }
 

tests/baselines/reference/neverReturningFunctions1.js

@@ -247,6 +247,20 @@ class SuperThrowable extends MyThrowable {
         this.throw()
     }
 }
+
+// Repro from #40346
+
+interface Services {
+    panic(message: string): never;
+}
+
+function foo(services: Readonly<Services>, s: string | null): string {
+    if (s === null) {
+        services.panic("ouch");
+    } else {
+        return s;
+    }
+}
 
 
 //// [neverReturningFunctions1.js]
@@ -467,6 +481,14 @@ var SuperThrowable = /** @class */ (function (_super) {
     };
     return SuperThrowable;
 }(MyThrowable));
+function foo(services, s) {
+    if (s === null) {
+        services.panic("ouch");
+    }
+    else {
+        return s;
+    }
+}
 
 
 //// [neverReturningFunctions1.d.ts]

tests/baselines/reference/neverReturningFunctions1.symbols

@@ -635,3 +635,34 @@ class SuperThrowable extends MyThrowable {
     }
 }
 
+// Repro from #40346
+
+interface Services {
+>Services : Symbol(Services, Decl(neverReturningFunctions1.ts, 247, 1))
+
+    panic(message: string): never;
+>panic : Symbol(Services.panic, Decl(neverReturningFunctions1.ts, 251, 20))
+>message : Symbol(message, Decl(neverReturningFunctions1.ts, 252, 10))
+}
+
+function foo(services: Readonly<Services>, s: string | null): string {
+>foo : Symbol(foo, Decl(neverReturningFunctions1.ts, 253, 1))
+>services : Symbol(services, Decl(neverReturningFunctions1.ts, 255, 13))
+>Readonly : Symbol(Readonly, Decl(lib.es5.d.ts, --, --))
+>Services : Symbol(Services, Decl(neverReturningFunctions1.ts, 247, 1))
+>s : Symbol(s, Decl(neverReturningFunctions1.ts, 255, 42))
+
+    if (s === null) {
+>s : Symbol(s, Decl(neverReturningFunctions1.ts, 255, 42))
+
+        services.panic("ouch");
+>services.panic : Symbol(panic, Decl(neverReturningFunctions1.ts, 251, 20))
+>services : Symbol(services, Decl(neverReturningFunctions1.ts, 255, 13))
+>panic : Symbol(panic, Decl(neverReturningFunctions1.ts, 251, 20))
+
+    } else {
+        return s;
+>s : Symbol(s, Decl(neverReturningFunctions1.ts, 255, 42))
+    }
+}
+

tests/baselines/reference/neverReturningFunctions1.types

@@ -706,3 +706,35 @@ class SuperThrowable extends MyThrowable {
     }
 }
 
+// Repro from #40346
+
+interface Services {
+    panic(message: string): never;
+>panic : (message: string) => never
+>message : string
+}
+
+function foo(services: Readonly<Services>, s: string | null): string {
+>foo : (services: Readonly<Services>, s: string | null) => string
+>services : Readonly<Services>
+>s : string | null
+>null : null
+
+    if (s === null) {
+>s === null : boolean
+>s : string | null
+>null : null
+
+        services.panic("ouch");
+>services.panic("ouch") : never
+>services.panic : (message: string) => never
+>services : Readonly<Services>
+>panic : (message: string) => never
+>"ouch" : "ouch"
+
+    } else {
+        return s;
+>s : string
+    }
+}
+

tests/cases/conformance/controlFlow/neverReturningFunctions1.ts

@@ -250,3 +250,17 @@ class SuperThrowable extends MyThrowable {
         this.throw()
     }
 }
+
+// Repro from #40346
+
+interface Services {
+    panic(message: string): never;
+}
+
+function foo(services: Readonly<Services>, s: string | null): string {
+    if (s === null) {
+        services.panic("ouch");
+    } else {
+        return s;
+    }
+}