Disable the import of private dependencies when using precise invocations.

ModuleFileSharedCore::getTransitiveLoadingBehavior() has a
best-effort mode that is enabled when debugger support is turned
on that will try to import implementation-only imports of Swift
modules, but won't treat import failures as errors. When explicit
modules are on, this has the unwanted side-effect of potentially
triggering an implicit Clang module build if one of the internal
dependencies of a library was not used to build the target.

I previously fixed this problem by turning off implicit modules while
loading the context dependencies. However, we discovered that the
transitive loading of private dependencies can also lead to additional
Swift modules being pulled in that through their dependencies can lead
to dependency cycles that were not a problem at build time.

Therefore, a simpler solution to both problem is turning of private
dependency import altogether when using precise compiler invocations.

Note that private dependencies can still sneak into a context via type
reconstruction, which can also trigger module imports.

rdar://132360374

Author: adrian-prantl

lldb/source/Plugins/TypeSystem/Swift/SwiftASTContext.cpp

@@ -1018,6 +1018,20 @@ void SwiftASTContext::SetCompilerInvocationLLDBOverrides() {
   swift::LangOptions &lang_opts = m_compiler_invocation_ap->getLangOptions();
   lang_opts.AllowDeserializingImplementationOnly = true;
   lang_opts.DebuggerSupport = true;
+
+  // ModuleFileSharedCore::getTransitiveLoadingBehavior() has a
+  // best-effort mode that is enabled when debugger support is turned
+  // on that will try to import implementation-only imports of Swift
+  // modules, but won't treat import failures as errors. When explicit
+  // modules are on, this has the unwanted side-effect of potentially
+  // triggering an implicit Clang module build if one of the internal
+  // dependencies of a library was not used to build the target. It
+  // can also lead to additional Swift modules being pulled in that
+  // through their dependencies can lead to dependency cycles that
+  // were not a problem at build time.
+  bool is_precise = ModuleList::GetGlobalModuleListProperties()
+                        .GetUseSwiftPreciseCompilerInvocation();
+  lang_opts.ImportNonPublicDependencies = is_precise ? false : true;
   // When loading Swift types that conform to ObjC protocols that have
   // been renamed with NS_SWIFT_NAME the DwarfImporterDelegate will crash
   // during protocol conformance checks as the underlying type cannot be
@@ -9212,42 +9226,6 @@ bool SwiftASTContext::GetCompileUnitImportsImpl(
 
   LOG_PRINTF(GetLog(LLDBLog::Types), "Importing dependencies of current CU");
 
-  // Turn off implicit clang modules while importing CU dependencies.
-  // ModuleFileSharedCore::getTransitiveLoadingBehavior() has a
-  // best-effort mode that is enabled when debugger support is turned
-  // on that will try to import implementation-only imports of Swift
-  // modules, but won't treat import failures as errors. When explicit
-  // modules are on, this has the unwanted side-effect of potentially
-  // triggering an implicit Clang module build if one of the internal
-  // dependencies of a library was not used to build the target. To
-  // avoid these costly and potentially dangerous imports we turn off
-  // implicit modules while importing the CU imports only. If a user
-  // manually evaluates an expression that contains an import
-  // statement that can still trigger an implict import.  Implicit
-  // imports can be dangerous if an implicit module depends on a
-  // module that also exists as an explicit input: In this case, a
-  // subsequent explicit import of said dependency will error because
-  // Clang now knows about two versions of the same module.
-  clang::LangOptions *clang_lang_opts = nullptr;
-  auto reset = llvm::make_scope_exit([&] {
-    if (clang_lang_opts) {
-      LOG_PRINTF(GetLog(LLDBLog::Types), "Turning on implicit Clang modules");
-      clang_lang_opts->ImplicitModules = true;
-    }
-  });
-  if (auto *clang_importer = GetClangImporter()) {
-    if (m_has_explicit_modules) {
-      auto &clang_instance = const_cast<clang::CompilerInstance &>(
-          clang_importer->getClangInstance());
-      clang_lang_opts = &clang_instance.getLangOpts();
-      // AddExtraArgs is supposed to always turn implicit modules on.
-      assert(clang_lang_opts->ImplicitModules &&
-             "ClangImporter implicit module support is off");
-      LOG_PRINTF(GetLog(LLDBLog::Types), "Turning off implicit Clang modules");
-      clang_lang_opts->ImplicitModules = false;
-    }
-  }
-  
   std::string category = "Importing Swift module dependencies for ";
   category += compile_unit->GetPrimaryFile().GetFilename();
   Progress progress(category, "", cu_imports.size());

lldb/test/API/lang/swift/clangimporter/explict_noimplicit/TestSwiftClangImporterExplicitNoImplicit.py

@@ -30,6 +30,4 @@ def test(self):
                     substrs=["hidden"])
         self.filecheck('platform shell cat "%s"' % log, __file__)
 #       CHECK-NOT: IMPLICIT-CLANG-MODULE-CACHE/{{.*}}/SwiftShims-{{.*}}.pcm
-#       CHECK: Turning off implicit Clang modules
 #       CHECK: IMPLICIT-CLANG-MODULE-CACHE/{{.*}}/Hidden-{{.*}}.pcm
-#       CHECK: Turning on implicit Clang modules

lldb/test/API/lang/swift/private_import/TestSwiftPrivateImport.py

@@ -16,17 +16,24 @@ def test_private_import(self):
         os.unlink(self.getBuildArtifact("Invisible.swiftmodule"))
         os.unlink(self.getBuildArtifact("Invisible.swiftinterface"))
 
-        if lldb.remote_platform:
-            wd = lldb.remote_platform.GetWorkingDirectory()
-            filename = 'libInvisible.dylib'
-            err = lldb.remote_platform.Put(
-                lldb.SBFileSpec(self.getBuildArtifact(filename)),
-                lldb.SBFileSpec(os.path.join(wd, filename)))
-            self.assertFalse(err.Fail(), 'Failed to copy ' + filename)
-
+        log = self.getBuildArtifact("types.log")
+        self.expect('log enable lldb types -f "%s"' % log)
         lldbutil.run_to_source_breakpoint(
             self, 'break here', lldb.SBFileSpec('main.swift'),
-            extra_images=['Library'])
+            extra_images=['Library', 'Invisible'])
+
+        precise = self.dbg.GetSetting('symbols.swift-precise-compiler-invocation').GetBooleanValue()
+        if precise:
+            # Test that importing the expression context (i.e., the module
+            # "a") pulls in the explicit dependencies, but not their
+            # private imports.  This comes before the other checks,
+            # because type reconstruction will still trigger an import of
+            # the "Invisible" module that we can't prevent later one.
+            self.expect("expression 1+1")
+            self.filecheck('platform shell cat "%s"' % log, __file__)
+#           CHECK:  Module import remark: loaded module 'Library'
+#           CHECK-NOT: Module import remark: loaded module 'Invisible'
+
         self.expect("fr var -d run -- x", substrs=["(Invisible.InvisibleStruct)"])
-        # FIXME: This crashes LLDB with a Swift DESERIALIZATION FAILURE.
-        # self.expect("fr var -d run -- y", substrs=["(Any)"])
+        self.expect("fr var -d run -- y", substrs=["(Library.Conforming)",
+                                                   "conforming"])