Fix issue #22923

src/compiler/checker.ts

@@ -16406,9 +16406,13 @@ namespace ts {
                 }
             }
             const suggestion = getSuggestionForNonexistentProperty(propNode, containingType);
+            const promisedType = getPromisedTypeOfPromise(containingType);
             if (suggestion !== undefined) {
                 errorInfo = chainDiagnosticMessages(errorInfo, Diagnostics.Property_0_does_not_exist_on_type_1_Did_you_mean_2, declarationNameToString(propNode), typeToString(containingType), suggestion);
             }
+            else if (promisedType && getPropertyOfType(promisedType, propNode.escapedText)) {
+                errorInfo = chainDiagnosticMessages(errorInfo, Diagnostics.Property_0_does_not_exist_on_type_1_Did_you_forget_to_await_the_1, declarationNameToString(propNode), typeToString(containingType));
+            }
             else {
                 errorInfo = chainDiagnosticMessages(errorInfo, Diagnostics.Property_0_does_not_exist_on_type_1, declarationNameToString(propNode), typeToString(containingType));
             }

src/compiler/diagnosticMessages.json

@@ -2000,7 +2000,10 @@
         "category": "Error",
         "code": 2569
     },
-
+    "Property '{0}' does not exist on type '{1}'. Did you forget to await the '{1}'?": {
+        "category": "Error",
+        "code": 2570
+    },
     "JSX element attributes type '{0}' may not be a union type.": {
         "category": "Error",
         "code": 2600

tests/baselines/reference/missingPropertyOfPromise.errors.txt

@@ -0,0 +1,10 @@
+tests/cases/compiler/missingPropertyOfPromise.ts(2,7): error TS2570: Property 'toLowerCase' does not exist on type 'Promise<string>'. Did you forget to await the 'Promise<string>'?
+
+
+==== tests/cases/compiler/missingPropertyOfPromise.ts (1 errors) ====
+    function f(x: Promise<string>) {
+        x.toLowerCase();
+          ~~~~~~~~~~~
+!!! error TS2570: Property 'toLowerCase' does not exist on type 'Promise<string>'. Did you forget to await the 'Promise<string>'?
+    }
+

tests/baselines/reference/missingPropertyOfPromise.js

@@ -0,0 +1,10 @@
+//// [missingPropertyOfPromise.ts]
+function f(x: Promise<string>) {
+    x.toLowerCase();
+}
+
+
+//// [missingPropertyOfPromise.js]
+function f(x) {
+    x.toLowerCase();
+}

tests/baselines/reference/missingPropertyOfPromise.symbols

@@ -0,0 +1,10 @@
+=== tests/cases/compiler/missingPropertyOfPromise.ts ===
+function f(x: Promise<string>) {
+>f : Symbol(f, Decl(missingPropertyOfPromise.ts, 0, 0))
+>x : Symbol(x, Decl(missingPropertyOfPromise.ts, 0, 11))
+>Promise : Symbol(Promise, Decl(lib.d.ts, --, --))
+
+    x.toLowerCase();
+>x : Symbol(x, Decl(missingPropertyOfPromise.ts, 0, 11))
+}
+

tests/baselines/reference/missingPropertyOfPromise.types

@@ -0,0 +1,13 @@
+=== tests/cases/compiler/missingPropertyOfPromise.ts ===
+function f(x: Promise<string>) {
+>f : (x: Promise<string>) => void
+>x : Promise<string>
+>Promise : Promise<T>
+
+    x.toLowerCase();
+>x.toLowerCase() : any
+>x.toLowerCase : any
+>x : Promise<string>
+>toLowerCase : any
+}
+

tests/cases/compiler/missingPropertyOfPromise.ts

@@ -0,0 +1,3 @@
+function f(x: Promise<string>) {
+    x.toLowerCase();
+}