make ModulePassContext conform to CustomStringConvertible

and let its description return a dump of the whole module.
This is useful for debugging

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/PassManager/ModulePassContext.swift

@@ -18,9 +18,14 @@ import OptimizerBridging
 /// It provides access to all functions, v-tables and witness tables of a module,
 /// but it doesn't provide any APIs to modify functions.
 /// In order to modify a function, a module pass must use `transform(function:)`.
-struct ModulePassContext : Context {
+struct ModulePassContext : Context, CustomStringConvertible {
   let _bridged: BridgedPassContext
 
+  public var description: String {
+    let stdString = _bridged.getModuleDescription()
+    return String(_cxxString: stdString)
+  }
+
   struct FunctionList : CollectionLikeSequence, IteratorProtocol {
     private var currentFunction: Function?
 

include/swift/SILOptimizer/OptimizerBridging.h

@@ -149,6 +149,8 @@ struct BridgedPostDomTree {
 struct BridgedPassContext {
   swift::SwiftPassInvocation * _Nonnull invocation;
 
+  std::string getModuleDescription() const;
+
   SWIFT_IMPORT_UNSAFE
   BridgedChangeNotificationHandler asNotificationHandler() const {
     return {invocation};

lib/SILOptimizer/PassManager/PassManager.cpp

@@ -1417,6 +1417,14 @@ void BridgedChangeNotificationHandler::notifyChanges(Kind changeKind) const {
   }
 }
 
+std::string BridgedPassContext::getModuleDescription() const {
+  std::string str;
+  llvm::raw_string_ostream os(str);
+  invocation->getPassManager()->getModule()->print(os);
+  str.pop_back(); // Remove trailing newline.
+  return str;
+}
+
 bool BridgedPassContext::tryDeleteDeadClosure(BridgedInstruction closure) const {
   return ::tryDeleteDeadClosure(closure.getAs<SingleValueInstruction>(), InstModCallbacks());
 }