Fix a case where snippet is specified twice

When importing a file across multiple locations in a module make sure it
doesn't trip an assert and it works as expected.

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

@@ -2378,12 +2378,12 @@ impl<'a> Context<'a> {
 impl<'a, 'b> SubContext<'a, 'b> {
     pub fn generate(&mut self) -> Result<(), Error> {
         for m in self.program.local_modules.iter() {
-            // All local modules we find should be unique, so assert such.
-            assert!(self
-                .cx
-                .local_modules
-                .insert(m.identifier, m.contents)
-                .is_none());
+            // All local modules we find should be unique, but the same module
+            // may have showed up in a few different blocks. If that's the case
+            // all the same identifiers should have the same contents.
+            if let Some(prev) = self.cx.local_modules.insert(m.identifier, m.contents) {
+                assert_eq!(prev, m.contents);
+            }
         }
         for f in self.program.exports.iter() {
             self.generate_export(f).with_context(|_| {

tests/headless/snippets.rs

@@ -4,6 +4,14 @@ use wasm_bindgen_test::*;
 #[wasm_bindgen(module = "/tests/headless/snippets1.js")]
 extern {
     fn get_two() -> u32;
+    #[wasm_bindgen(js_name = get_stateful)]
+    fn get_stateful1() -> u32;
+}
+
+#[wasm_bindgen(module = "/tests/headless/snippets1.js")]
+extern {
+    #[wasm_bindgen(js_name = get_stateful)]
+    fn get_stateful2() -> u32;
 }
 
 #[wasm_bindgen_test]
@@ -11,6 +19,14 @@ fn test_get_two() {
     assert_eq!(get_two(), 2);
 }
 
+#[wasm_bindgen_test]
+fn stateful_deduplicated() {
+    assert_eq!(get_stateful1(), 1);
+    assert_eq!(get_stateful2(), 2);
+    assert_eq!(get_stateful1(), 3);
+    assert_eq!(get_stateful2(), 4);
+}
+
 #[wasm_bindgen(inline_js = "export function get_three() { return 3; }")]
 extern {
     fn get_three() -> u32;

tests/headless/snippets1.js

@@ -1,3 +1,9 @@
 export function get_two() {
   return 2;
 }
+
+let a = 0;
+export function get_stateful() {
+  a += 1;
+  return a;
+}