[ScanDependencies] Fix a memory leak in dependency graph

Fix a memory leak from #75134.

(cherry picked from commit 180e8d4)

Author: cachemeifyoucan

lib/DependencyScan/ScanDependencies.cpp

@@ -591,12 +591,10 @@ static void bridgeDependencyIDs(const ArrayRef<ModuleDependencyID> dependencies,
 
 static swiftscan_macro_dependency_set_t *createMacroDependencySet(
     const std::map<std::string, MacroPluginDependency> &macroDeps) {
+  if (macroDeps.empty())
+    return nullptr;
+
   swiftscan_macro_dependency_set_t *set = new swiftscan_macro_dependency_set_t;
-  if (macroDeps.empty()) {
-    set->count = 0;
-    set->macro_dependencies = nullptr;
-    return set;
-  }
   set->count = macroDeps.size();
   set->macro_dependencies = new swiftscan_macro_dependency_t[set->count];
   unsigned SI = 0;

tools/libSwiftScan/libSwiftScan.cpp

@@ -31,12 +31,16 @@ DEFINE_SIMPLE_CONVERSION_FUNCTIONS(DependencyScanningTool, swiftscan_scanner_t)
 //=== Private Cleanup Functions -------------------------------------------===//
 void swiftscan_macro_dependency_dispose(
     swiftscan_macro_dependency_set_t *macro) {
+  if (!macro)
+    return;
+
   for (unsigned i = 0; i < macro->count; ++i) {
     swiftscan_string_dispose(macro->macro_dependencies[i]->moduleName);
     swiftscan_string_dispose(macro->macro_dependencies[i]->libraryPath);
     swiftscan_string_dispose(macro->macro_dependencies[i]->executablePath);
     delete macro->macro_dependencies[i];
   }
+  delete[] macro->macro_dependencies;
   delete macro;
 }