Port TS#63043: Implement walkBindingPattern for declaration emit of destructured parameter properties (#2751)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: jakebailey <5341706+jakebailey@users.noreply.github.com>

Author: Copilot

internal/transformers/declarations/transform.go

@@ -1430,7 +1430,7 @@ func (tx *DeclarationTransformer) transformClassDeclaration(input *ast.ClassDecl
 				parameterProperties = append(parameterProperties, updated)
 			} else {
 				// Pattern - this is currently an error, but we emit declarations for it somewhat correctly
-				// !!! is this worth reimplementing? We never made it not-an-error
+				parameterProperties = append(parameterProperties, tx.walkBindingPattern(param.Name().AsBindingPattern(), param)...)
 			}
 		}
 		tx.state.getSymbolAccessibilityDiagnostic = oldDiag
@@ -1542,6 +1542,27 @@ func (tx *DeclarationTransformer) transformClassDeclaration(input *ast.ClassDecl
 	)
 }
 
+func (tx *DeclarationTransformer) walkBindingPattern(pattern *ast.BindingPattern, param *ast.Node) []*ast.Node {
+	var elems []*ast.Node
+	for _, elem := range pattern.Elements.Nodes {
+		if ast.IsOmittedExpression(elem) {
+			continue
+		}
+		if ast.IsBindingPattern(elem.Name()) {
+			elems = append(elems, tx.walkBindingPattern(elem.Name().AsBindingPattern(), param)...)
+			continue
+		}
+		elems = append(elems, tx.Factory().NewPropertyDeclaration(
+			tx.ensureModifiers(param),
+			elem.Name(),
+			nil, /*questionOrExclamationToken*/
+			tx.ensureType(elem, false),
+			nil, /*initializer*/
+		))
+	}
+	return elems
+}
+
 func (tx *DeclarationTransformer) transformVariableStatement(input *ast.VariableStatement) *ast.Node {
 	visible := false
 	for _, decl := range input.DeclarationList.AsVariableDeclarationList().Declarations.Nodes {

testdata/baselines/reference/submodule/compiler/declarationEmitDestructuringParameterProperties.js

@@ -36,10 +36,16 @@ class C3 {
 
 //// [declarationEmitDestructuringParameterProperties.d.ts]
 declare class C1 {
+    x: string;
+    y: string;
+    z: string;
     constructor([x, y, z]: string[]);
 }
 type TupleType1 = [string, number, boolean];
 declare class C2 {
+    x: string;
+    y: number;
+    z: boolean;
     constructor([x, y, z]: TupleType1);
 }
 type ObjType1 = {
@@ -48,5 +54,8 @@ type ObjType1 = {
     z: boolean;
 };
 declare class C3 {
+    x: number;
+    y: string;
+    z: boolean;
     constructor({ x, y, z }: ObjType1);
 }

testdata/baselines/reference/submodule/compiler/declarationEmitDestructuringParameterProperties.js.diff

@@ -36,10 +36,16 @@ class C3 {
 
 //// [declarationEmitDestructuringParameterProperties2.d.ts]
 declare class C1 {
+    x: string;
+    y: string;
+    z: string;
     constructor([x, y, z]: string[]);
 }
 type TupleType1 = [string, number, boolean];
 declare class C2 {
+    x: string;
+    y: number;
+    z: boolean;
     constructor([x, y, z]: TupleType1);
 }
 type ObjType1 = {
@@ -48,5 +54,8 @@ type ObjType1 = {
     z: boolean;
 };
 declare class C3 {
+    x: number;
+    y: string;
+    z: boolean;
     constructor({ x, y, z }: ObjType1);
 }