FineModuleTrace: avoid emitting trace file when lazy type checking is enabled.

When lazy type checking is enabled, the generated AST to walk on may contain function bodies that
are not fully type-checked. Walking on these function bodies could expose latent bugs.

Resolves rdar://140818215

Author: nkcsgexi

lib/FrontendTool/LoadedModuleTrace.cpp

@@ -917,6 +917,10 @@ static void createFineModuleTraceFile(const InputFile &input, ModuleDecl *MD) {
 
 bool swift::emitFineModuleTraceIfNeeded(ModuleDecl *mainModule,
                                         const FrontendOptions &opts) {
+  // When lazy type checking is enabled, we may end up with a partial AST.
+  // Walking on these partial AST completely may expose latent bugs.
+  if (mainModule->getASTContext().TypeCheckerOpts.EnableLazyTypecheck)
+    return false;
   ASTContext &ctxt = mainModule->getASTContext();
   assert(!ctxt.hadError() &&
          "We should've already exited earlier if there was an error.");

test/IDE/objc_send_collector_1.swift

@@ -7,6 +7,9 @@
 // RUN: SWIFT_COMPILER_FINE_GRAINED_TRACE_PATH=%t/given_trace.json %target-swift-frontend  -I %t/lib/swift -typecheck %s %S/Inputs/objc_send_collector_2.swift -module-name main -swift-version 5 -F %S/Inputs/mock-sdk -emit-loaded-module-trace-path %t/.MODULE_TRACE
 // RUN: cat %t/given_trace.json | %{python} -c 'import json, sys; json.dump(json.loads(sys.stdin.read()), sys.stdout, sort_keys=True, indent=2)' | %FileCheck %s
 
+// RUN: SWIFT_COMPILER_FINE_GRAINED_TRACE_PATH=%t/given_trace_2.json %target-swift-frontend  -I %t/lib/swift -typecheck %s %S/Inputs/objc_send_collector_2.swift -module-name main -swift-version 5 -F %S/Inputs/mock-sdk -emit-loaded-module-trace-path %t/.MODULE_TRACE -enable-library-evolution -experimental-lazy-typecheck
+// RUN: not ls %t/given_trace_2.json
+
 // REQUIRES: objc_interop
 
 import Foo