Strip nullable types from 'this' type in inference with optional chain calls (microsoft#42536)

* Properly strip nullable types from this type in optional chain calls

* Add regression test

Author: ahejlsberg

src/compiler/checker.ts

@@ -27160,6 +27160,16 @@ namespace ts {
             return getInferredTypes(context);
         }
 
+        function getThisArgumentType(thisArgumentNode: LeftHandSideExpression | undefined) {
+            if (!thisArgumentNode) {
+                return voidType;
+            }
+            const thisArgumentType = checkExpression(thisArgumentNode);
+            return isOptionalChainRoot(thisArgumentNode.parent) ? getNonNullableType(thisArgumentType) :
+                isOptionalChain(thisArgumentNode.parent) ? removeOptionalTypeMarker(thisArgumentType) :
+                thisArgumentType;
+        }
+
         function inferTypeArguments(node: CallLikeExpression, signature: Signature, args: readonly Expression[], checkMode: CheckMode, context: InferenceContext): Type[] {
             if (isJsxOpeningLikeElement(node)) {
                 return inferJsxTypeArguments(node, signature, checkMode, context);
@@ -27215,8 +27225,7 @@ namespace ts {
             const thisType = getThisTypeOfSignature(signature);
             if (thisType) {
                 const thisArgumentNode = getThisArgumentOfCall(node);
-                const thisArgumentType = thisArgumentNode ? checkExpression(thisArgumentNode) : voidType;
-                inferTypes(context.inferences, thisArgumentType, thisType);
+                inferTypes(context.inferences, getThisArgumentType(thisArgumentNode), thisType);
             }
 
             for (let i = 0; i < argCount; i++) {
@@ -27457,20 +27466,7 @@ namespace ts {
                 // If the signature's 'this' type is voidType, then the check is skipped -- anything is compatible.
                 // If the expression is a new expression, then the check is skipped.
                 const thisArgumentNode = getThisArgumentOfCall(node);
-                let thisArgumentType: Type;
-                if (thisArgumentNode) {
-                    thisArgumentType = checkExpression(thisArgumentNode);
-                    if (isOptionalChainRoot(thisArgumentNode.parent)) {
-                        thisArgumentType = getNonNullableType(thisArgumentType);
-                    }
-                    else if (isOptionalChain(thisArgumentNode.parent)) {
-                        thisArgumentType = removeOptionalTypeMarker(thisArgumentType);
-                    }
-                }
-                else {
-                    thisArgumentType = voidType;
-                }
-
+                const thisArgumentType = getThisArgumentType(thisArgumentNode);
                 const errorNode = reportErrors ? (thisArgumentNode || node) : undefined;
                 const headMessage = Diagnostics.The_this_context_of_type_0_is_not_assignable_to_method_s_this_of_type_1;
                 if (!checkTypeRelatedTo(thisArgumentType, thisType, relation, errorNode, headMessage, containingMessageChain, errorOutputContainer)) {

tests/baselines/reference/callChainInference.js

@@ -0,0 +1,25 @@
+//// [callChainInference.ts]
+// Repro from #42404
+
+interface Y {
+    foo<T>(this: T, arg: keyof T): void;
+    a: number;
+    b: string;
+}
+
+declare const value: Y | undefined;
+
+if (value) {
+    value?.foo("a");
+}
+
+value?.foo("a");
+
+
+//// [callChainInference.js]
+"use strict";
+// Repro from #42404
+if (value) {
+    value === null || value === void 0 ? void 0 : value.foo("a");
+}
+value === null || value === void 0 ? void 0 : value.foo("a");

tests/baselines/reference/callChainInference.symbols

@@ -0,0 +1,39 @@
+=== tests/cases/conformance/expressions/optionalChaining/callChain/callChainInference.ts ===
+// Repro from #42404
+
+interface Y {
+>Y : Symbol(Y, Decl(callChainInference.ts, 0, 0))
+
+    foo<T>(this: T, arg: keyof T): void;
+>foo : Symbol(Y.foo, Decl(callChainInference.ts, 2, 13))
+>T : Symbol(T, Decl(callChainInference.ts, 3, 8))
+>this : Symbol(this, Decl(callChainInference.ts, 3, 11))
+>T : Symbol(T, Decl(callChainInference.ts, 3, 8))
+>arg : Symbol(arg, Decl(callChainInference.ts, 3, 19))
+>T : Symbol(T, Decl(callChainInference.ts, 3, 8))
+
+    a: number;
+>a : Symbol(Y.a, Decl(callChainInference.ts, 3, 40))
+
+    b: string;
+>b : Symbol(Y.b, Decl(callChainInference.ts, 4, 14))
+}
+
+declare const value: Y | undefined;
+>value : Symbol(value, Decl(callChainInference.ts, 8, 13))
+>Y : Symbol(Y, Decl(callChainInference.ts, 0, 0))
+
+if (value) {
+>value : Symbol(value, Decl(callChainInference.ts, 8, 13))
+
+    value?.foo("a");
+>value?.foo : Symbol(Y.foo, Decl(callChainInference.ts, 2, 13))
+>value : Symbol(value, Decl(callChainInference.ts, 8, 13))
+>foo : Symbol(Y.foo, Decl(callChainInference.ts, 2, 13))
+}
+
+value?.foo("a");
+>value?.foo : Symbol(Y.foo, Decl(callChainInference.ts, 2, 13))
+>value : Symbol(value, Decl(callChainInference.ts, 8, 13))
+>foo : Symbol(Y.foo, Decl(callChainInference.ts, 2, 13))
+

tests/baselines/reference/callChainInference.types

@@ -0,0 +1,37 @@
+=== tests/cases/conformance/expressions/optionalChaining/callChain/callChainInference.ts ===
+// Repro from #42404
+
+interface Y {
+    foo<T>(this: T, arg: keyof T): void;
+>foo : <T>(this: T, arg: keyof T) => void
+>this : T
+>arg : keyof T
+
+    a: number;
+>a : number
+
+    b: string;
+>b : string
+}
+
+declare const value: Y | undefined;
+>value : Y | undefined
+
+if (value) {
+>value : Y | undefined
+
+    value?.foo("a");
+>value?.foo("a") : void
+>value?.foo : <T>(this: T, arg: keyof T) => void
+>value : Y
+>foo : <T>(this: T, arg: keyof T) => void
+>"a" : "a"
+}
+
+value?.foo("a");
+>value?.foo("a") : void | undefined
+>value?.foo : (<T>(this: T, arg: keyof T) => void) | undefined
+>value : Y | undefined
+>foo : (<T>(this: T, arg: keyof T) => void) | undefined
+>"a" : "a"
+

tests/cases/conformance/expressions/optionalChaining/callChain/callChainInference.ts

@@ -0,0 +1,17 @@
+// @strict: true
+
+// Repro from #42404
+
+interface Y {
+    foo<T>(this: T, arg: keyof T): void;
+    a: number;
+    b: string;
+}
+
+declare const value: Y | undefined;
+
+if (value) {
+    value?.foo("a");
+}
+
+value?.foo("a");