Emit JS library aliases after non-alias library items

When a JS library alias target (e.g. `foo`) is visited first and
transitively depends on its own alias (e.g. `foo_alias: 'foo'`),
`addedLibraryItems['foo']` is marked as visited before `var _foo = ...`
is emitted. Emitting `var _foo_alias = _foo;` inline during dependency
traversal causes it to appear before `var _foo = ...`, leaving
`_foo_alias` initialized to `undefined` for arrow functions and
non-hoisted values.

Collect JS library alias assignments in `libraryAliases` and emit them
after `libraryItems` (and before `postSets`) so all target symbols are
defined before any alias assignment runs.

Author: sbc100

src/jsifier.mjs

@@ -414,6 +414,7 @@ const PROXY_SYNC_ASYNC = 2;
 
 export async function runJSify(outputFile, symbolsOnly) {
   const libraryItems = [];
+  const libraryAliases = [];
   const symbolDeps = {};
   const asyncFuncs = [];
   let postSets = [];
@@ -728,11 +729,12 @@ function(${args}) {
         }
       }
 
+      let aliasTarget;
       if (LibraryManager.isAlias(snippet)) {
         // Redirection for aliases. We include the parent, and at runtime
         // make ourselves equal to it.  This avoid having duplicate
         // functions with identical content.
-        const aliasTarget = snippet;
+        aliasTarget = snippet;
         if (WASM_EXPORTS.has(aliasTarget)) {
           debugLog(`native alias: ${mangled} -> ${aliasTarget}`);
           nativeAliases[mangled] = aliasTarget;
@@ -884,6 +886,15 @@ function(${args}) {
             .filter((x) => x != '')
             .join('\n') + '\n'
         : '';
+      // Defer direct JS value aliases (`var _alias = _target;`) to `libraryAliases`
+      // so the target symbol is guaranteed to be defined first. Skip native
+      // aliases (which emit no code here) and signature-mismatch aliases (where
+      // `isFunction` is set because they are emitted as forwarding wrapper
+      // functions rather than immediate value assignments).
+      if (aliasTarget && !isNativeAlias && !isFunction) {
+        libraryAliases.push(commentText + contentText);
+        return depsText.trim();
+      }
       return depsText + commentText + contentText;
     }
 
@@ -928,7 +939,7 @@ function(${args}) {
     includeSystemFile(preFile);
 
     writeOutput('// Begin JS library code\n');
-    for (const item of libraryItems.concat(postSets)) {
+    for (const item of [...libraryItems, ...libraryAliases, ...postSets]) {
       writeOutput(indentify(item ?? '', 2));
     }
     writeOutput('// End JS library code\n');

test/codesize/test_codesize_hello_dylink_all.json

@@ -1,7 +1,7 @@
 {
-  "a.out.js": 272709,
+  "a.out.js": 272705,
   "a.out.nodebug.wasm": 588152,
-  "total": 860861,
+  "total": 860857,
   "sent": [
     "IMG_Init",
     "IMG_Load",

test/test_jslib.py

@@ -604,7 +604,15 @@ def test_jslib_include(self):
   def test_jslib_aliases(self, args):
     create_file('foo.js', '''
       addToLibrary({
-        foo: () => 42,
+        // Create a dependency cycle (foo -> $call_alias -> foo_alias -> foo)
+        // to test that `var _foo_alias = _foo;` is still emitted after `_foo`.
+        $call_alias__deps: ['foo_alias'],
+        $call_alias: () => _foo_alias(),
+        foo__deps: ['$call_alias'],
+        foo: () => {
+          if (!call_alias) return 0;
+          return 42;
+        },
         foo__sig: 'i',
 
         foo_alias: 'foo',