Expose loadStructInfo JS macro function add additional struct/macro definitions. (#22251)

Eventually it would be nice to enable external use of the
gen_struct_info.py script to generate these things, but this is a step
in that direction.

Author: sbc100

src/modules.mjs

@@ -285,15 +285,23 @@ function addToLibrary(obj, options = null) {
 let structs = {};
 let defines = {};
 
+/**
+ * Read JSON file containing struct and macro/define information
+ * that can then be used in JavaScript via macros.
+ */
+function loadStructInfo(filename) {
+  const temp = JSON.parse(read(filename));
+  Object.assign(structs, temp.structs);
+  Object.assign(defines, temp.defines);
+}
+
 if (!BOOTSTRAPPING_STRUCT_INFO) {
-  let structInfoFile = 'struct_info_generated.json';
+  // Load struct and define information.
   if (MEMORY64) {
-    structInfoFile = 'struct_info_generated_wasm64.json';
+    loadStructInfo('struct_info_generated_wasm64.json');
+  } else {
+    loadStructInfo('struct_info_generated.json');
   }
-  // Load struct and define information.
-  const temp = JSON.parse(read(structInfoFile));
-  structs = temp.structs;
-  defines = temp.defines;
 }
 
 // Use proxy objects for C_DEFINES and C_STRUCTS so that we can give useful
@@ -510,6 +518,7 @@ function exportRuntime() {
 
 addToCompileTimeContext({
   exportRuntime,
+  loadStructInfo,
   LibraryManager,
   librarySymbols,
   addToLibrary,

src/utility.mjs

@@ -328,6 +328,8 @@ export function loadSettingsFile(f) {
 }
 
 export function runInMacroContext(code, options) {
+  compileTimeContext['__filename'] = options.filename;
+  compileTimeContext['__dirname'] = path.dirname(options.filename);
   return vm.runInNewContext(code, compileTimeContext, options);
 }
 

test/other/test_extra_struct_info.js

@@ -0,0 +1,6 @@
+console.error("(before) AF_INET=" + {{{ cDefs.AF_INET }}});
+
+/* Loading this struct info file will override the default AF_INET value */
+{{{ loadStructInfo(__dirname + '/test_extra_struct_info.json'), null }}}
+
+console.error("(after) AF_INET=" + {{{ cDefs.AF_INET }}});

test/other/test_extra_struct_info.json

@@ -0,0 +1,5 @@
+{
+    "defines": {
+        "AF_INET": 42
+    }
+}

test/test_other.py

@@ -15010,3 +15010,8 @@ def test_save_temp(self):
     self.assertExists('hello_world.bc')
     # emcc takes care of creating the .o
     self.assertExists('hello_world.o')
+
+  def test_extra_struct_info(self):
+    stderr = self.run_process([EMCC, test_file('hello_world.c'), '--js-library', test_file('other/test_extra_struct_info.js')], stderr=PIPE).stderr
+    self.assertContained('(before) AF_INET=2', stderr)
+    self.assertContained('(after) AF_INET=42', stderr)