Ignore self tail calls when collecting the return type of a function

src/compiler/checker.ts

@@ -35614,6 +35614,14 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         forEachReturnStatement(func.body as Block, returnStatement => {
             const expr = returnStatement.expression;
             if (expr) {
+                // Bare calls to this same function don't contribute to inference
+                if (expr.kind === SyntaxKind.CallExpression &&
+                    (expr as CallExpression).expression.kind === SyntaxKind.Identifier &&
+                    checkExpressionCached((expr as CallExpression).expression).symbol === func.symbol) {
+                    hasReturnOfTypeNever = true;
+                    return;
+                }
+
                 let type = checkExpressionCached(expr, checkMode && checkMode & ~CheckMode.SkipGenericFunctions);
                 if (functionFlags & FunctionFlags.Async) {
                     // From within an async function you can return either a non-promise value or a promise. Any

tests/baselines/reference/callSignatureWithoutReturnTypeAnnotationInference.types

@@ -31,16 +31,16 @@ var r2 = foo2(1);
 >1 : 1
 
 function foo3() {
->foo3 : () => any
+>foo3 : () => never
 
     return foo3();
->foo3() : any
->foo3 : () => any
+>foo3() : never
+>foo3 : () => never
 }
 var r3 = foo3();
->r3 : any
->foo3() : any
->foo3 : () => any
+>r3 : never
+>foo3() : never
+>foo3 : () => never
 
 function foo4<T>(x: T) {
 >foo4 : <T>(x: T) => T

tests/baselines/reference/functionImplementations.errors.txt

@@ -1,7 +1,8 @@
+tests/cases/conformance/functions/functionImplementations.ts(85,5): error TS2403: Subsequent variable declarations must have the same type.  Variable 'a' must be of type 'any', but here has type 'Base'.
 tests/cases/conformance/functions/functionImplementations.ts(90,1): error TS2839: This condition will always return 'false' since JavaScript compares objects by reference, not value.
 
 
-==== tests/cases/conformance/functions/functionImplementations.ts (1 errors) ====
+==== tests/cases/conformance/functions/functionImplementations.ts (2 errors) ====
     // FunctionExpression with no return type annotation and no return statement returns void
     var v: void = function () { } ();
 
@@ -87,6 +88,9 @@ tests/cases/conformance/functions/functionImplementations.ts(90,1): error TS2839
 
     // FunctionExpression with no return type annotation with multiple return statements with one a recursive call
     var a = function f() {
+        ~
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'a' must be of type 'any', but here has type 'Base'.
+!!! related TS6203 tests/cases/conformance/functions/functionImplementations.ts:5:5: 'a' was also declared here.
         return new Base(); return new Derived(); return f(); // ?
     } ();
 

tests/baselines/reference/functionImplementations.types

@@ -17,12 +17,12 @@ var a: any = function f() {
 };
 var a: any = function f() {
 >a : any
->function f() {    return f();} : () => any
->f : () => any
+>function f() {    return f();} : () => never
+>f : () => never
 
     return f();
->f() : any
->f : () => any
+>f() : never
+>f : () => never
 
 };
 
@@ -205,17 +205,17 @@ var b = function () {
 // FunctionExpression with no return type annotation with multiple return statements with one a recursive call
 var a = function f() {
 >a : any
->function f() {    return new Base(); return new Derived(); return f(); // ?} () : any
->function f() {    return new Base(); return new Derived(); return f(); // ?} : () => any
->f : () => any
+>function f() {    return new Base(); return new Derived(); return f(); // ?} () : Base
+>function f() {    return new Base(); return new Derived(); return f(); // ?} : () => Base
+>f : () => Base
 
     return new Base(); return new Derived(); return f(); // ?
 >new Base() : Base
 >Base : typeof Base
 >new Derived() : Derived
 >Derived : typeof Derived
->f() : any
->f : () => any
+>f() : Base
+>f : () => Base
 
 } ();
 

tests/baselines/reference/implicitAnyFromCircularInference.errors.txt

@@ -2,15 +2,13 @@ tests/cases/compiler/implicitAnyFromCircularInference.ts(2,5): error TS2502: 'a'
 tests/cases/compiler/implicitAnyFromCircularInference.ts(5,5): error TS2502: 'b' is referenced directly or indirectly in its own type annotation.
 tests/cases/compiler/implicitAnyFromCircularInference.ts(6,5): error TS2502: 'c' is referenced directly or indirectly in its own type annotation.
 tests/cases/compiler/implicitAnyFromCircularInference.ts(9,5): error TS2502: 'd' is referenced directly or indirectly in its own type annotation.
-tests/cases/compiler/implicitAnyFromCircularInference.ts(14,10): error TS7023: 'g' implicitly has return type 'any' because it does not have a return type annotation and is referenced directly or indirectly in one of its return expressions.
-tests/cases/compiler/implicitAnyFromCircularInference.ts(17,5): error TS7023: 'f1' implicitly has return type 'any' because it does not have a return type annotation and is referenced directly or indirectly in one of its return expressions.
 tests/cases/compiler/implicitAnyFromCircularInference.ts(22,5): error TS7023: 'f2' implicitly has return type 'any' because it does not have a return type annotation and is referenced directly or indirectly in one of its return expressions.
 tests/cases/compiler/implicitAnyFromCircularInference.ts(25,10): error TS7023: 'h' implicitly has return type 'any' because it does not have a return type annotation and is referenced directly or indirectly in one of its return expressions.
 tests/cases/compiler/implicitAnyFromCircularInference.ts(27,14): error TS7023: 'foo' implicitly has return type 'any' because it does not have a return type annotation and is referenced directly or indirectly in one of its return expressions.
 tests/cases/compiler/implicitAnyFromCircularInference.ts(44,9): error TS7023: 'x' implicitly has return type 'any' because it does not have a return type annotation and is referenced directly or indirectly in one of its return expressions.
 
 
-==== tests/cases/compiler/implicitAnyFromCircularInference.ts (10 errors) ====
+==== tests/cases/compiler/implicitAnyFromCircularInference.ts (8 errors) ====
     // Error expected
     var a: typeof a;
         ~
@@ -33,13 +31,9 @@ tests/cases/compiler/implicitAnyFromCircularInference.ts(44,9): error TS7023: 'x
 
     // Error expected
     function g() { return g(); }
-             ~
-!!! error TS7023: 'g' implicitly has return type 'any' because it does not have a return type annotation and is referenced directly or indirectly in one of its return expressions.
 
     // Error expected
     var f1 = function () {
-        ~~
-!!! error TS7023: 'f1' implicitly has return type 'any' because it does not have a return type annotation and is referenced directly or indirectly in one of its return expressions.
         return f1();
     };
 

tests/baselines/reference/implicitAnyFromCircularInference.types

@@ -24,18 +24,18 @@ function f() { return f; }
 
 // Error expected
 function g() { return g(); }
->g : () => any
->g() : any
->g : () => any
+>g : () => never
+>g() : never
+>g : () => never
 
 // Error expected
 var f1 = function () {
->f1 : () => any
->function () {    return f1();} : () => any
+>f1 : () => never
+>function () {    return f1();} : () => never
 
     return f1();
->f1() : any
->f1 : () => any
+>f1() : never
+>f1 : () => never
 
 };
 

tests/baselines/reference/recursiveGenericSignatureInstantiation.types

@@ -1,11 +1,11 @@
 === tests/cases/compiler/recursiveGenericSignatureInstantiation.ts ===
 function f6<T>(x: T) {
->f6 : <T>(x: T) => any
+>f6 : <T>(x: T) => never
 >x : T
 
     return f6(x);
->f6(x) : any
->f6 : <T>(x: T) => any
+>f6(x) : never
+>f6 : <T>(x: T) => never
 >x : T
 }
 

tests/baselines/reference/simpleRecursionWithBaseCase.errors.txt

@@ -0,0 +1,54 @@
+tests/cases/compiler/simpleRecursionWithBaseCase.ts(8,21): error TS2554: Expected 1 arguments, but got 0.
+tests/cases/compiler/simpleRecursionWithBaseCase.ts(13,20): error TS2554: Expected 1 arguments, but got 0.
+tests/cases/compiler/simpleRecursionWithBaseCase.ts(19,20): error TS2345: Argument of type 'string' is not assignable to parameter of type 'number'.
+tests/cases/compiler/simpleRecursionWithBaseCase.ts(27,16): error TS2304: Cannot find name 'notfoundsymbol'.
+tests/cases/compiler/simpleRecursionWithBaseCase.ts(31,10): error TS7023: 'fn5' implicitly has return type 'any' because it does not have a return type annotation and is referenced directly or indirectly in one of its return expressions.
+
+
+==== tests/cases/compiler/simpleRecursionWithBaseCase.ts (5 errors) ====
+    function fn1(n: number) {
+        if (n === 0) {
+            return 3;
+        } else {
+            return fn1(n - 1);
+        }
+    }
+    const num: number = fn1();
+                        ~~~~~
+!!! error TS2554: Expected 1 arguments, but got 0.
+!!! related TS6210 tests/cases/compiler/simpleRecursionWithBaseCase.ts:1:14: An argument for 'n' was not provided.
+
+    function fn2(n: number) {
+        return fn2(n);
+    }
+    const nev: never = fn2();
+                       ~~~~~
+!!! error TS2554: Expected 1 arguments, but got 0.
+!!! related TS6210 tests/cases/compiler/simpleRecursionWithBaseCase.ts:10:14: An argument for 'n' was not provided.
+
+    function fn3(n: number) {
+        if (n === 0) {
+            return 3;
+        } else {
+            return fn1("hello world");
+                       ~~~~~~~~~~~~~
+!!! error TS2345: Argument of type 'string' is not assignable to parameter of type 'number'.
+        }
+    }
+
+    function fn4(n: number) {
+        if (n === 0) {
+            return 3;
+        } else {
+            return notfoundsymbol("hello world");
+                   ~~~~~~~~~~~~~~
+!!! error TS2304: Cannot find name 'notfoundsymbol'.
+        }
+    }
+
+    function fn5() {
+             ~~~
+!!! error TS7023: 'fn5' implicitly has return type 'any' because it does not have a return type annotation and is referenced directly or indirectly in one of its return expressions.
+        return [fn5][0]();
+    }
+

tests/baselines/reference/simpleRecursionWithBaseCase.js

@@ -0,0 +1,70 @@
+//// [simpleRecursionWithBaseCase.ts]
+function fn1(n: number) {
+    if (n === 0) {
+        return 3;
+    } else {
+        return fn1(n - 1);
+    }
+}
+const num: number = fn1();
+
+function fn2(n: number) {
+    return fn2(n);
+}
+const nev: never = fn2();
+
+function fn3(n: number) {
+    if (n === 0) {
+        return 3;
+    } else {
+        return fn1("hello world");
+    }
+}
+
+function fn4(n: number) {
+    if (n === 0) {
+        return 3;
+    } else {
+        return notfoundsymbol("hello world");
+    }
+}
+
+function fn5() {
+    return [fn5][0]();
+}
+
+
+//// [simpleRecursionWithBaseCase.js]
+"use strict";
+function fn1(n) {
+    if (n === 0) {
+        return 3;
+    }
+    else {
+        return fn1(n - 1);
+    }
+}
+var num = fn1();
+function fn2(n) {
+    return fn2(n);
+}
+var nev = fn2();
+function fn3(n) {
+    if (n === 0) {
+        return 3;
+    }
+    else {
+        return fn1("hello world");
+    }
+}
+function fn4(n) {
+    if (n === 0) {
+        return 3;
+    }
+    else {
+        return notfoundsymbol("hello world");
+    }
+}
+function fn5() {
+    return [fn5][0]();
+}

tests/baselines/reference/simpleRecursionWithBaseCase.symbols

@@ -0,0 +1,65 @@
+=== tests/cases/compiler/simpleRecursionWithBaseCase.ts ===
+function fn1(n: number) {
+>fn1 : Symbol(fn1, Decl(simpleRecursionWithBaseCase.ts, 0, 0))
+>n : Symbol(n, Decl(simpleRecursionWithBaseCase.ts, 0, 13))
+
+    if (n === 0) {
+>n : Symbol(n, Decl(simpleRecursionWithBaseCase.ts, 0, 13))
+
+        return 3;
+    } else {
+        return fn1(n - 1);
+>fn1 : Symbol(fn1, Decl(simpleRecursionWithBaseCase.ts, 0, 0))
+>n : Symbol(n, Decl(simpleRecursionWithBaseCase.ts, 0, 13))
+    }
+}
+const num: number = fn1();
+>num : Symbol(num, Decl(simpleRecursionWithBaseCase.ts, 7, 5))
+>fn1 : Symbol(fn1, Decl(simpleRecursionWithBaseCase.ts, 0, 0))
+
+function fn2(n: number) {
+>fn2 : Symbol(fn2, Decl(simpleRecursionWithBaseCase.ts, 7, 26))
+>n : Symbol(n, Decl(simpleRecursionWithBaseCase.ts, 9, 13))
+
+    return fn2(n);
+>fn2 : Symbol(fn2, Decl(simpleRecursionWithBaseCase.ts, 7, 26))
+>n : Symbol(n, Decl(simpleRecursionWithBaseCase.ts, 9, 13))
+}
+const nev: never = fn2();
+>nev : Symbol(nev, Decl(simpleRecursionWithBaseCase.ts, 12, 5))
+>fn2 : Symbol(fn2, Decl(simpleRecursionWithBaseCase.ts, 7, 26))
+
+function fn3(n: number) {
+>fn3 : Symbol(fn3, Decl(simpleRecursionWithBaseCase.ts, 12, 25))
+>n : Symbol(n, Decl(simpleRecursionWithBaseCase.ts, 14, 13))
+
+    if (n === 0) {
+>n : Symbol(n, Decl(simpleRecursionWithBaseCase.ts, 14, 13))
+
+        return 3;
+    } else {
+        return fn1("hello world");
+>fn1 : Symbol(fn1, Decl(simpleRecursionWithBaseCase.ts, 0, 0))
+    }
+}
+
+function fn4(n: number) {
+>fn4 : Symbol(fn4, Decl(simpleRecursionWithBaseCase.ts, 20, 1))
+>n : Symbol(n, Decl(simpleRecursionWithBaseCase.ts, 22, 13))
+
+    if (n === 0) {
+>n : Symbol(n, Decl(simpleRecursionWithBaseCase.ts, 22, 13))
+
+        return 3;
+    } else {
+        return notfoundsymbol("hello world");
+    }
+}
+
+function fn5() {
+>fn5 : Symbol(fn5, Decl(simpleRecursionWithBaseCase.ts, 28, 1))
+
+    return [fn5][0]();
+>fn5 : Symbol(fn5, Decl(simpleRecursionWithBaseCase.ts, 28, 1))
+}
+