fix(42238): emit this parameter in function declaration (#46511)

src/compiler/checker.ts

@@ -5657,8 +5657,8 @@ namespace ts {
                 const expandedParams = getExpandedParameters(signature, /*skipUnionExpanding*/ true)[0];
                 // If the expanded parameter list had a variadic in a non-trailing position, don't expand it
                 const parameters = (some(expandedParams, p => p !== expandedParams[expandedParams.length - 1] && !!(getCheckFlags(p) & CheckFlags.RestParameter)) ? signature.parameters : expandedParams).map(parameter => symbolToParameterDeclaration(parameter, context, kind === SyntaxKind.Constructor, options?.privateSymbolVisitor, options?.bundledImports));
-                if (signature.thisParameter) {
-                    const thisParameter = symbolToParameterDeclaration(signature.thisParameter, context);
+                const thisParameter = tryGetThisParameterDeclaration(signature, context);
+                if (thisParameter) {
                     parameters.unshift(thisParameter);
                 }
 
@@ -5713,6 +5713,25 @@ namespace ts {
                 return node;
             }
 
+            function tryGetThisParameterDeclaration(signature: Signature, context: NodeBuilderContext) {
+                if (signature.thisParameter) {
+                    return symbolToParameterDeclaration(signature.thisParameter, context);
+                }
+                if (signature.declaration) {
+                    const thisTag = getJSDocThisTag(signature.declaration);
+                    if (thisTag && thisTag.typeExpression) {
+                        return factory.createParameterDeclaration(
+                            /* decorators */ undefined,
+                            /* modifiers */ undefined,
+                            /* dotDotDotToken */ undefined,
+                            "this",
+                            /* questionToken */ undefined,
+                            typeToTypeNodeHelper(getTypeFromTypeNode(thisTag.typeExpression), context)
+                        );
+                    }
+                }
+            }
+
             function typeParameterToDeclarationWithConstraint(type: TypeParameter, context: NodeBuilderContext, constraintNode: TypeNode | undefined): TypeParameterDeclaration {
                 const savedContextFlags = context.flags;
                 context.flags &= ~NodeBuilderFlags.WriteTypeParametersInQualifiedName; // Avoids potential infinite loop when building for a claimspace with a generic

tests/baselines/reference/thisTag1.types

@@ -4,7 +4,7 @@
  * @return {number}
  */
 function f(s) {
->f : (s: string) => number
+>f : (this: { n: number; }, s: string) => number
 >s : string
 
     return this.n + s.length
@@ -18,20 +18,20 @@ function f(s) {
 }
 
 const o = {
->o : { f: (s: string) => number; n: number; }
->{    f,    n: 1} : { f: (s: string) => number; n: number; }
+>o : { f: (this: { n: number; }, s: string) => number; n: number; }
+>{    f,    n: 1} : { f: (this: { n: number; }, s: string) => number; n: number; }
 
     f,
->f : (s: string) => number
+>f : (this: { n: number; }, s: string) => number
 
     n: 1
 >n : number
 >1 : 1
 }
 o.f('hi')
 >o.f('hi') : number
->o.f : (s: string) => number
->o : { f: (s: string) => number; n: number; }
->f : (s: string) => number
+>o.f : (this: { n: number; }, s: string) => number
+>o : { f: (this: { n: number; }, s: string) => number; n: number; }
+>f : (this: { n: number; }, s: string) => number
 >'hi' : "hi"
 

tests/baselines/reference/thisTag2.js

@@ -0,0 +1,15 @@
+//// [a.js]
+/** @this {string} */
+export function f1() {}
+
+/** @this */
+export function f2() {}
+
+
+
+
+//// [a.d.ts]
+/** @this {string} */
+export function f1(this: string): void;
+/** @this */
+export function f2(this: any): void;

tests/baselines/reference/thisTag2.symbols

@@ -0,0 +1,9 @@
+=== tests/cases/conformance/jsdoc/a.js ===
+/** @this {string} */
+export function f1() {}
+>f1 : Symbol(f1, Decl(a.js, 0, 0))
+
+/** @this */
+export function f2() {}
+>f2 : Symbol(f2, Decl(a.js, 1, 23))
+

tests/baselines/reference/thisTag2.types

@@ -0,0 +1,9 @@
+=== tests/cases/conformance/jsdoc/a.js ===
+/** @this {string} */
+export function f1() {}
+>f1 : (this: string) => void
+
+/** @this */
+export function f2() {}
+>f2 : (this: any) => void
+

tests/cases/conformance/jsdoc/thisTag2.ts

@@ -0,0 +1,11 @@
+// @target: esnext
+// @allowJs: true
+// @declaration: true
+// @emitDeclarationOnly: true
+// @filename: a.js
+
+/** @this {string} */
+export function f1() {}
+
+/** @this */
+export function f2() {}