Investigate: No floating promises

src/compiler/checker.ts

@@ -23000,6 +23000,10 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         return reduceLeft(types, (s, t) => isTypeSubtypeOf(t, s) ? t : s)!;
     }
 
+    function isPromiseType(type: Type): type is TypeReference {
+        return !!(getObjectFlags(type) & ObjectFlags.Reference) && ((type as TypeReference).target === getGlobalPromiseType(/*reportErrors*/ false));
+    }
+
     function isArrayType(type: Type): type is TypeReference {
         return !!(getObjectFlags(type) & ObjectFlags.Reference) && ((type as TypeReference).target === globalArrayType || (type as TypeReference).target === globalReadonlyArrayType);
     }
@@ -40818,7 +40822,10 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         // Grammar checking
         checkGrammarStatementInAmbientContext(node);
 
-        checkExpression(node.expression);
+        const exprType = checkExpression(node.expression);
+        if (!isAssignmentExpression(node.expression, /*excludeCompoundAssignment*/ true) && isPromiseType(exprType)) {
+            error(node.expression, Diagnostics.A_Promise_must_be_awaited_returned_or_explicitly_ignored_with_the_void_operator);
+        }
     }
 
     function checkIfStatement(node: IfStatement) {

src/compiler/diagnosticMessages.json

@@ -6427,6 +6427,10 @@
         "category": "Error",
         "code": 7061
     },
+    "A Promise must be awaited, returned, or explicitly ignored with the 'void' operator": {
+        "category": "Error",
+        "code": 7062
+    },
 
     "You cannot rename this element.": {
         "category": "Error",

src/server/session.ts

@@ -2790,7 +2790,7 @@ export class Session<TMessage = string> implements EventSender {
         const commands = args.command as CodeActionCommand | CodeActionCommand[]; // They should be sending back the command we sent them.
         for (const command of toArray(commands)) {
             const { file, project } = this.getFileAndProject(command);
-            project.getLanguageService().applyCodeActionCommand(command, this.getFormatOptions(file)).then(
+            void project.getLanguageService().applyCodeActionCommand(command, this.getFormatOptions(file)).then(
                 _result => { /* TODO: GH#20447 report success message? */ },
                 _error => { /* TODO: GH#20447 report errors */ });
         }

tests/baselines/reference/asyncAwaitNestedClasses_es5.errors.txt

@@ -0,0 +1,21 @@
+tests/cases/conformance/async/es5/asyncAwaitNestedClasses_es5.ts(15,1): error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
+
+
+==== tests/cases/conformance/async/es5/asyncAwaitNestedClasses_es5.ts (1 errors) ====
+    // https://github.com/Microsoft/TypeScript/issues/20744
+    class A {
+        static B = class B {
+            static func2(): Promise<void> {
+                return new Promise((resolve) => { resolve(null); });
+            }
+            static C = class C {
+                static async func() {
+                    await B.func2();
+                }
+            }
+        }
+    }
+
+    A.B.C.func();
+    ~~~~~~~~~~~~
+!!! error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator

tests/baselines/reference/asyncIIFE.errors.txt

@@ -0,0 +1,18 @@
+tests/cases/compiler/asyncIIFE.ts(2,5): error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
+
+
+==== tests/cases/compiler/asyncIIFE.ts (1 errors) ====
+    function f1() {
+        (async () => {
+        ~~~~~~~~~~~~~~
+            await 10
+    ~~~~~~~~~~~~~~~~
+            throw new Error();
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~
+        })();
+    ~~~~~~~~
+!!! error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
+
+        var x = 1;
+    }
+

tests/baselines/reference/asyncImportNestedYield.errors.txt

@@ -0,0 +1,9 @@
+tests/cases/compiler/asyncImportNestedYield.ts(2,5): error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
+
+
+==== tests/cases/compiler/asyncImportNestedYield.ts (1 errors) ====
+    async function* foo() {
+        import((await import(yield "foo")).default);
+        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
+    }

tests/baselines/reference/awaitedType.errors.txt

@@ -1,9 +1,10 @@
 tests/cases/compiler/awaitedType.ts(22,12): error TS2589: Type instantiation is excessively deep and possibly infinite.
 tests/cases/compiler/awaitedType.ts(26,12): error TS2589: Type instantiation is excessively deep and possibly infinite.
+tests/cases/compiler/awaitedType.ts(234,3): error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
 tests/cases/compiler/awaitedType.ts(236,28): error TS2493: Tuple type '[number]' of length '1' has no element at index '1'.
 
 
-==== tests/cases/compiler/awaitedType.ts (3 errors) ====
+==== tests/cases/compiler/awaitedType.ts (4 errors) ====
     type T1 = Awaited<number>;
     type T2 = Awaited<Promise<number>>;
     type T3 = Awaited<number | Promise<number>>;
@@ -242,11 +243,16 @@ tests/cases/compiler/awaitedType.ts(236,28): error TS2493: Tuple type '[number]'
       const promises = [Promise.resolve(0)] as const
 
       Promise.all(promises).then((results) => {
+      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         const first = results[0]
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         const second = results[1] // error
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                ~
 !!! error TS2493: Tuple type '[number]' of length '1' has no element at index '1'.
       })
+    ~~~~
+!!! error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
     }
 
     // repro from #40330

tests/baselines/reference/blockScopedVariablesUseBeforeDef.errors.txt

@@ -5,9 +5,11 @@ tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts(100,12): error TS2448:
 tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts(111,28): error TS2448: Block-scoped variable 'a' used before its declaration.
 tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts(112,21): error TS2448: Block-scoped variable 'a' used before its declaration.
 tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts(122,22): error TS2448: Block-scoped variable 'a' used before its declaration.
+tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts(127,9): error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
+tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts(130,9): error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
 
 
-==== tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts (7 errors) ====
+==== tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts (9 errors) ====
     function foo0() {
         let a = x;
                 ~
@@ -156,9 +158,13 @@ tests/cases/compiler/blockScopedVariablesUseBeforeDef.ts(122,22): error TS2448:
     function foo17() {
         const promise = (async () => {
             promise
+            ~~~~~~~
+!!! error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
             foo
             await null
             promise
+            ~~~~~~~
+!!! error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
             foo
         })()
 

tests/baselines/reference/bundlerSyntaxRestrictions.errors.txt

@@ -2,6 +2,7 @@ error TS2468: Cannot find global value 'Promise'.
 /main.ts(2,1): error TS1202: Import assignment cannot be used when targeting ECMAScript modules. Consider using 'import * as ns from "mod"', 'import {a} from "mod"', 'import d from "mod"', or another module format instead.
 /main.ts(3,1): error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
 /mainJs.js(2,1): error TS2712: A dynamic import call in ES5/ES3 requires the 'Promise' constructor.  Make sure you have a declaration for the 'Promise' constructor or include 'ES2015' in your '--lib' option.
+/mainJs.js(2,1): error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
 
 
 !!! error TS2468: Cannot find global value 'Promise'.
@@ -20,11 +21,13 @@ error TS2468: Cannot find global value 'Promise'.
         export = path; // ok
     }
 
-==== /mainJs.js (1 errors) ====
+==== /mainJs.js (2 errors) ====
     import {} from "./a";
     import("./a");
     ~~~~~~~~~~~~~
 !!! error TS2712: A dynamic import call in ES5/ES3 requires the 'Promise' constructor.  Make sure you have a declaration for the 'Promise' constructor or include 'ES2015' in your '--lib' option.
+    ~~~~~~~~~~~~~
+!!! error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
     const _ = require("./a"); // No resolution
     _.a; // any
 

tests/baselines/reference/callWithSpread4.errors.txt

@@ -1,8 +1,10 @@
+tests/cases/conformance/expressions/functionCalls/callWithSpread4.ts(16,1): error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
 tests/cases/conformance/expressions/functionCalls/callWithSpread4.ts(18,5): error TS2556: A spread argument must either have a tuple type or be passed to a rest parameter.
 tests/cases/conformance/expressions/functionCalls/callWithSpread4.ts(27,6): error TS2556: A spread argument must either have a tuple type or be passed to a rest parameter.
+tests/cases/conformance/expressions/functionCalls/callWithSpread4.ts(29,1): error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
 
 
-==== tests/cases/conformance/expressions/functionCalls/callWithSpread4.ts (2 errors) ====
+==== tests/cases/conformance/expressions/functionCalls/callWithSpread4.ts (4 errors) ====
     type R = { a: number }
     type W = { b: number }
     type RW = { a: number, b: number }
@@ -19,15 +21,24 @@ tests/cases/conformance/expressions/functionCalls/callWithSpread4.ts(27,6): erro
     declare var gz: RW[]
     declare var fun: (inp: any) => AsyncGenerator<string, void, unknown>
     pli(
+    ~~~~
         reads,
+    ~~~~~~~~~~
         ...gun,
+    ~~~~~~~~~~~
         ~~~~~~
 !!! error TS2556: A spread argument must either have a tuple type or be passed to a rest parameter.
         tr,
+    ~~~~~~~
         fun,
+    ~~~~~~~~
         ...gz,
+    ~~~~~~~~~~
         writes
+    ~~~~~~~~~~
     );
+    ~
+!!! error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
 
     declare function test(x: any, y: () => string): string | undefined;
     declare var anys: any[]
@@ -36,4 +47,6 @@ tests/cases/conformance/expressions/functionCalls/callWithSpread4.ts(27,6): erro
 !!! error TS2556: A spread argument must either have a tuple type or be passed to a rest parameter.
 
     pli(...[reads, writes, writes] as const)
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
 

tests/baselines/reference/controlFlowIIFE.errors.txt

@@ -1,8 +1,9 @@
 tests/cases/conformance/controlFlow/controlFlowIIFE.ts(64,5): error TS2454: Variable 'v' is used before being assigned.
+tests/cases/conformance/controlFlow/controlFlowIIFE.ts(69,5): error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
 tests/cases/conformance/controlFlow/controlFlowIIFE.ts(72,5): error TS2454: Variable 'v' is used before being assigned.
 
 
-==== tests/cases/conformance/controlFlow/controlFlowIIFE.ts (2 errors) ====
+==== tests/cases/conformance/controlFlow/controlFlowIIFE.ts (3 errors) ====
     declare function getStringOrNumber(): string | number;
 
     function f1() {
@@ -74,8 +75,12 @@ tests/cases/conformance/controlFlow/controlFlowIIFE.ts(72,5): error TS2454: Vari
     function f6() {
         let v: number;
         (async function() {
+        ~~~~~~~~~~~~~~~~~~~
             v = await 1;
+    ~~~~~~~~~~~~~~~~~~~~
         })();
+    ~~~~~~~~
+!!! error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
         v; // still undefined
         ~
 !!! error TS2454: Variable 'v' is used before being assigned.

tests/baselines/reference/defaultExportInAwaitExpression01.errors.txt

@@ -0,0 +1,18 @@
+tests/cases/conformance/es6/modules/b.ts(3,1): error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
+
+
+==== tests/cases/conformance/es6/modules/a.ts (0 errors) ====
+    const x = new Promise( ( resolve, reject ) => { resolve( {} ); } );
+    export default x;
+
+==== tests/cases/conformance/es6/modules/b.ts (1 errors) ====
+    import x from './a';
+
+    ( async function() {
+    ~~~~~~~~~~~~~~~~~~~~
+        const value = await x;
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~
+    }() );
+    ~~~~~
+!!! error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
+

tests/baselines/reference/defaultExportInAwaitExpression02.errors.txt

@@ -0,0 +1,18 @@
+tests/cases/conformance/es6/modules/b.ts(3,1): error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
+
+
+==== tests/cases/conformance/es6/modules/a.ts (0 errors) ====
+    const x = new Promise( ( resolve, reject ) => { resolve( {} ); } );
+    export default x;
+
+==== tests/cases/conformance/es6/modules/b.ts (1 errors) ====
+    import x from './a';
+
+    ( async function() {
+    ~~~~~~~~~~~~~~~~~~~~
+        const value = await x;
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~
+    }() );
+    ~~~~~
+!!! error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
+

tests/baselines/reference/destructureOfVariableSameAsShorthand.errors.txt

@@ -0,0 +1,40 @@
+tests/cases/compiler/destructureOfVariableSameAsShorthand.ts(10,5): error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
+tests/cases/compiler/destructureOfVariableSameAsShorthand.ts(14,5): error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
+
+
+==== tests/cases/compiler/destructureOfVariableSameAsShorthand.ts (2 errors) ====
+    // https://github.com/microsoft/TypeScript/issues/38969
+    interface AxiosResponse<T = never> {
+        data: T;
+    }
+
+    declare function get<T = never, R = AxiosResponse<T>>(): Promise<R>;
+
+    async function main() {
+        // These work examples as expected
+        get().then((response) => {
+        ~~~~~~~~~~~~~~~~~~~~~~~~~~
+            // body is never
+    ~~~~~~~~~~~~~~~~~~~~~~~~
+            const body = response.data;
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+        })
+    ~~~~~~
+!!! error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
+        get().then(({ data }) => {
+        ~~~~~~~~~~~~~~~~~~~~~~~~~~
+            // data is never
+    ~~~~~~~~~~~~~~~~~~~~~~~~
+        })
+    ~~~~~~
+!!! error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
+        const response = await get()
+        // body is never
+        const body = response.data;
+        // data is never
+        const { data } = await get<never>();
+
+        // The following did not work as expected.
+        // shouldBeNever should be never, but was any
+        const { data: shouldBeNever } = await get();
+    }

tests/baselines/reference/dynamicImportEvaluateSpecifier.errors.txt

@@ -0,0 +1,24 @@
+tests/cases/compiler/dynamicImportEvaluateSpecifier.ts(4,1): error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
+tests/cases/compiler/dynamicImportEvaluateSpecifier.ts(5,1): error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
+
+
+==== tests/cases/compiler/dynamicImportEvaluateSpecifier.ts (2 errors) ====
+    // https://github.com/microsoft/TypeScript/issues/48285
+    let i = 0;
+
+    import(String(i++));
+    ~~~~~~~~~~~~~~~~~~~
+!!! error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
+    import(String(i++));
+    ~~~~~~~~~~~~~~~~~~~
+!!! error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
+
+    const getPath = async () => {
+    	/* in reality this would do some async FS operation, or a web request */
+    	return "/root/my/cool/path";
+    };
+
+    const someFunction = async () => {
+    	const result = await import(await getPath());
+    };
+

tests/baselines/reference/dynamicImportTrailingComma.errors.txt

@@ -1,8 +1,11 @@
+tests/cases/compiler/dynamicImportTrailingComma.ts(2,1): error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
 tests/cases/compiler/dynamicImportTrailingComma.ts(2,12): error TS1009: Trailing comma not allowed.
 
 
-==== tests/cases/compiler/dynamicImportTrailingComma.ts (1 errors) ====
+==== tests/cases/compiler/dynamicImportTrailingComma.ts (2 errors) ====
     const path = './foo';
     import(path,);
+    ~~~~~~~~~~~~~
+!!! error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
                ~
 !!! error TS1009: Trailing comma not allowed.

tests/baselines/reference/dynamicImportWithNestedThis_es2015.errors.txt

@@ -0,0 +1,17 @@
+tests/cases/compiler/dynamicImportWithNestedThis_es2015.ts(11,1): error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator
+
+
+==== tests/cases/compiler/dynamicImportWithNestedThis_es2015.ts (1 errors) ====
+    // https://github.com/Microsoft/TypeScript/issues/17564
+    class C {
+    	private _path = './other';
+
+    	dynamic() {
+    		return import(this._path);
+    	}
+    }
+
+    const c = new C();
+    c.dynamic();
+    ~~~~~~~~~~~
+!!! error TS7062: A Promise must be awaited, returned, or explicitly ignored with the 'void' operator