Implement shim_format

crates/cli-support/src/intrinsic.rs

@@ -84,6 +84,10 @@ fn opt_i64() -> Descriptor {
     Descriptor::Option(Box::new(Descriptor::I64))
 }
 
+fn opt_u32() -> Descriptor {
+    Descriptor::Option(Box::new(Descriptor::U32))
+}
+
 fn slice(contents: Descriptor) -> Descriptor {
     Descriptor::Ref(Box::new(Descriptor::Slice(Box::new(contents))))
 }
@@ -276,5 +280,11 @@ intrinsics! {
         #[symbol = "__wbindgen_init_externref_table"]
         #[signature = fn() -> Unit]
         InitExternrefTable,
+        #[symbol = "__wbindgen_shim_format_variant"]
+        #[signature = fn() -> opt_u32()]
+        ShimFormatVariant,
+        #[symbol = "__wbindgen_shim_format_string"]
+        #[signature = fn() -> String]
+        ShimFormatString,
     }
 }

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

@@ -3551,6 +3551,17 @@ impl<'a> Context<'a> {
                 }
                 base
             }
+
+            Intrinsic::ShimFormatVariant => match &self.config.mode {
+                OutputMode::Web => 0.to_string(),
+                OutputMode::NoModules { .. } => 1.to_string(),
+                _ => String::from("null"),
+            },
+
+            Intrinsic::ShimFormatString => match &self.config.mode {
+                OutputMode::NoModules { global } => format!("'{global}'"),
+                _ => String::from("undefined"),
+            },
         };
         Ok(expr)
     }

src/lib.rs

@@ -1083,6 +1083,9 @@ externs! {
         fn __wbindgen_memory() -> u32;
         fn __wbindgen_module() -> u32;
         fn __wbindgen_function_table() -> u32;
+
+        fn __wbindgen_shim_format_variant() -> WasmOption<u32>;
+        fn __wbindgen_shim_format_string() -> WasmSlice;
     }
 }
 
@@ -1367,6 +1370,40 @@ pub fn function_table() -> JsValue {
     unsafe { JsValue::_new(__wbindgen_function_table()) }
 }
 
+/// Represents the format of the shim.
+#[derive(Clone, Debug)]
+#[non_exhaustive]
+pub enum ShimFormat {
+    /// The shim is an ES module.
+    EsModule,
+    /// The shim doesn't use any module system, and instead exposes a global variable
+    /// with its API.
+    ///
+    /// It has to be imported as a script to work properly, as the global variable is
+    /// created by simply declaring a top-level variable, which only works in scripts.
+    NoModules {
+        /// The name of the global variable the shim exposes.
+        ///
+        /// By default, this is `"wasm_bindgen"`.
+        global_name: String,
+    },
+}
+
+/// Returns the format of the generated JS shim.
+///
+/// This will currently return `None` on every target except `web` and `no-modules`.
+pub fn shim_format() -> Option<ShimFormat> {
+    match unsafe { __wbindgen_shim_format_variant() } {
+        WasmOption::Some(0) => Some(ShimFormat::EsModule),
+        WasmOption::Some(1) => {
+            let global_name = unsafe { String::from_abi(__wbindgen_shim_format_string()) };
+            Some(ShimFormat::NoModules { global_name })
+        }
+        WasmOption::Some(_) => unreachable!("unexpected variant identifier"),
+        WasmOption::None => None,
+    }
+}
+
 #[doc(hidden)]
 pub mod __rt {
     use crate::JsValue;