Use private constructors in type definitions of structs without an ex…

…ported constructor (#4282)

CHANGELOG.md

@@ -96,6 +96,9 @@
 * Fixed imports for functions using `this` and late binding.
   [#4225](https://github.com/rustwasm/wasm-bindgen/pull/4225)
 
+* Don't expose non-functioning implicit constructors to classes when none are provided.
+  [#4282](https://github.com/rustwasm/wasm-bindgen/pull/4282)
+
 --------------------------------------------------------------------------------
 
 ## [0.2.95](https://github.com/rustwasm/wasm-bindgen/compare/0.2.94...0.2.95)

crates/cli-support/src/js/mod.rs

@@ -1016,14 +1016,19 @@ __wbg_set_wasm(wasm);"
         let mut dst = format!("class {} {{\n", name);
         let mut ts_dst = format!("export {}", dst);
 
-        if self.config.debug && !class.has_constructor {
-            dst.push_str(
-                "
-                    constructor() {
-                        throw new Error('cannot invoke `new` directly');
-                    }
-                ",
-            );
+        if !class.has_constructor {
+            // declare the constructor as private to prevent direct instantiation
+            ts_dst.push_str("  private constructor();\n");
+
+            if self.config.debug {
+                dst.push_str(
+                    "
+                        constructor() {
+                            throw new Error('cannot invoke `new` directly');
+                        }
+                    ",
+                );
+            }
         }
 
         if class.wrap_needed {

crates/cli/tests/reference/builder.d.ts

@@ -1,6 +1,7 @@
 /* tslint:disable */
 /* eslint-disable */
 export class ClassBuilder {
+  private constructor();
   free(): void;
   static builder(): ClassBuilder;
 }

crates/cli/tests/reference/echo.d.ts

@@ -57,5 +57,6 @@ export function echo_option_vec_string(a?: (string)[]): (string)[] | undefined;
 export function echo_option_struct(a?: Foo): Foo | undefined;
 export function echo_option_vec_struct(a?: (Foo)[]): (Foo)[] | undefined;
 export class Foo {
+  private constructor();
   free(): void;
 }

crates/cli/tests/reference/getter-setter.d.ts

@@ -1,6 +1,7 @@
 /* tslint:disable */
 /* eslint-disable */
 export class Foo {
+  private constructor();
   free(): void;
   x: number;
   y?: number;

crates/cli/tests/reference/raw.d.ts

@@ -2,6 +2,7 @@
 /* eslint-disable */
 export function test1(test: number): number;
 export class Test {
+  private constructor();
   free(): void;
   static test1(test: number): Test;
   test2(test: number): void;

crates/typescript-tests/src/custom_section.rs

@@ -17,3 +17,11 @@ const _: &str = TS_INTERFACE_EXPORT2;
 pub struct Person {
     pub height: u32,
 }
+
+#[wasm_bindgen]
+impl Person {
+    #[wasm_bindgen(constructor)]
+    pub fn new() -> Self {
+        Self { height: 170 }
+    }
+}

crates/typescript-tests/src/getters_setters.rs

@@ -10,6 +10,16 @@ pub struct ColorWithGetters {
 
 #[wasm_bindgen]
 impl ColorWithGetters {
+    #[wasm_bindgen(constructor)]
+    pub fn new() -> Self {
+        Self {
+            r: 0.0,
+            _g: 0.0,
+            _b: 0.0,
+            _a: 0,
+        }
+    }
+
     #[wasm_bindgen(getter)]
     pub fn r(&self) -> f64 {
         self.r
@@ -31,6 +41,16 @@ pub struct ColorWithSetters {
 
 #[wasm_bindgen]
 impl ColorWithSetters {
+    #[wasm_bindgen(constructor)]
+    pub fn new() -> Self {
+        Self {
+            r: 0.0,
+            _g: 0.0,
+            _b: 0.0,
+            a: 0,
+        }
+    }
+
     #[wasm_bindgen(setter)]
     pub fn set_r(&mut self, r: f64) {
         self.r = r;
@@ -57,6 +77,16 @@ pub struct ColorWithGetterAndSetter {
 
 #[wasm_bindgen]
 impl ColorWithGetterAndSetter {
+    #[wasm_bindgen(constructor)]
+    pub fn new() -> Self {
+        Self {
+            r: 0.0,
+            _g: 0.0,
+            _b: 0.0,
+            a: 0,
+        }
+    }
+
     #[wasm_bindgen(getter)]
     pub fn r(&self) -> f64 {
         self.r