[ASTContext] Add setter for LLDB callback

`PreModuleImportCallback` is a variable for a callback function used
specifically by LLDB to report progress updates on importing Swift
modules in LLDB. This commit adds a setter for `PreModuleImportCallback`
for greater flexibility in LLDB and removes the reference to this
variable in the constructor.

Related to swiftlang/llvm-project#7769

rdar://105286354

Author: chelcassanova

include/swift/AST/ASTContext.h

@@ -239,8 +239,8 @@ class ASTContext final {
       ClangImporterOptions &ClangImporterOpts,
       symbolgraphgen::SymbolGraphOptions &SymbolGraphOpts,
       SourceManager &SourceMgr, DiagnosticEngine &Diags,
-      llvm::IntrusiveRefCntPtr<llvm::vfs::OutputBackend> OutBackend = nullptr,
-      std::function<bool(llvm::StringRef, bool)> PreModuleImportCallback = {});
+      llvm::IntrusiveRefCntPtr<llvm::vfs::OutputBackend> OutBackend = nullptr
+      );
 
 public:
   // Members that should only be used by ASTContext.cpp.
@@ -257,8 +257,8 @@ class ASTContext final {
       ClangImporterOptions &ClangImporterOpts,
       symbolgraphgen::SymbolGraphOptions &SymbolGraphOpts,
       SourceManager &SourceMgr, DiagnosticEngine &Diags,
-      llvm::IntrusiveRefCntPtr<llvm::vfs::OutputBackend> OutBackend = nullptr,
-      std::function<bool(llvm::StringRef, bool)> PreModuleImportCallback = {});
+      llvm::IntrusiveRefCntPtr<llvm::vfs::OutputBackend> OutBackend = nullptr
+      );
   ~ASTContext();
 
   /// Optional table of counters to report, nullptr when not collecting.
@@ -294,6 +294,8 @@ class ASTContext final {
   /// OutputBackend for writing outputs.
   llvm::IntrusiveRefCntPtr<llvm::vfs::OutputBackend> OutputBackend;
 
+  void SetPreModuleImportCallback(std::function<bool(llvm::StringRef ModuleName, bool IsOverlay)> callback);
+
   /// If the shared pointer is not a \c nullptr and the pointee is \c true,
   /// all operations working on this ASTContext should be aborted at the next
   /// possible opportunity.

lib/AST/ASTContext.cpp

@@ -629,8 +629,8 @@ ASTContext *ASTContext::get(
     ClangImporterOptions &ClangImporterOpts,
     symbolgraphgen::SymbolGraphOptions &SymbolGraphOpts,
     SourceManager &SourceMgr, DiagnosticEngine &Diags,
-    llvm::IntrusiveRefCntPtr<llvm::vfs::OutputBackend> OutputBackend,
-    std::function<bool(llvm::StringRef, bool)> PreModuleImportCallback) {
+    llvm::IntrusiveRefCntPtr<llvm::vfs::OutputBackend> OutputBackend
+    ) {
   // If more than two data structures are concatentated, then the aggregate
   // size math needs to become more complicated due to per-struct alignment
   // constraints.
@@ -644,7 +644,7 @@ ASTContext *ASTContext::get(
   return new (mem)
       ASTContext(langOpts, typecheckOpts, silOpts, SearchPathOpts,
                  ClangImporterOpts, SymbolGraphOpts, SourceMgr, Diags,
-                 std::move(OutputBackend), PreModuleImportCallback);
+                 std::move(OutputBackend));
 }
 
 ASTContext::ASTContext(
@@ -653,16 +653,15 @@ ASTContext::ASTContext(
     ClangImporterOptions &ClangImporterOpts,
     symbolgraphgen::SymbolGraphOptions &SymbolGraphOpts,
     SourceManager &SourceMgr, DiagnosticEngine &Diags,
-    llvm::IntrusiveRefCntPtr<llvm::vfs::OutputBackend> OutBackend,
-    std::function<bool(llvm::StringRef, bool)> PreModuleImportCallback)
+    llvm::IntrusiveRefCntPtr<llvm::vfs::OutputBackend> OutBackend
+    )
     : LangOpts(langOpts), TypeCheckerOpts(typecheckOpts), SILOpts(silOpts),
       SearchPathOpts(SearchPathOpts), ClangImporterOpts(ClangImporterOpts),
       SymbolGraphOpts(SymbolGraphOpts), SourceMgr(SourceMgr), Diags(Diags),
       OutputBackend(std::move(OutBackend)), evaluator(Diags, langOpts),
       TheBuiltinModule(createBuiltinModule(*this)),
       StdlibModuleName(getIdentifier(STDLIB_NAME)),
       SwiftShimsModuleName(getIdentifier(SWIFT_SHIMS_NAME)),
-      PreModuleImportCallback(PreModuleImportCallback),
       TheErrorType(new (*this, AllocationArena::Permanent) ErrorType(
           *this, Type(), RecursiveTypeProperties::HasError)),
       TheUnresolvedType(new(*this, AllocationArena::Permanent)
@@ -715,6 +714,10 @@ ASTContext::~ASTContext() {
   getImpl().~Implementation();
 }
 
+void ASTContext::SetPreModuleImportCallback(std::function<bool(llvm::StringRef ModuleName, bool IsOverlay)> callback) {
+  ASTContext::PreModuleImportCallback = callback;
+}
+
 llvm::BumpPtrAllocator &ASTContext::getAllocator(AllocationArena arena) const {
   switch (arena) {
   case AllocationArena::Permanent: