Turn off PCM validation by default.

These diagnostics are useful when debugging LLDB and project
configurations, but in a live debug session they mostly get in the
way. Especially when using explicit modules mismatches in warning
options caused by implicitly triggered imports are not really
actionable fo users outside of clearing their module cache and trying
again.

rdar://130284825
(cherry picked from commit babe4b2)

Author: adrian-prantl

lldb/include/lldb/Target/Target.h

@@ -188,6 +188,8 @@ class TargetProperties : public Properties {
 
   bool GetSwiftAllowExplicitModules() const;
 
+  AutoBool GetSwiftPCMValidation() const;
+
   Args GetSwiftPluginServerForPath() const;
 
   bool GetSwiftAutoImportFrameworks() const;

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

@@ -57,7 +57,9 @@
 #include "clang/Basic/TargetOptions.h"
 #include "clang/Driver/Driver.h"
 #include "clang/Frontend/CompilerInstance.h"
+#include "clang/Lex/Preprocessor.h"
 
+#include "clang/Lex/PreprocessorOptions.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
@@ -9225,6 +9227,38 @@ bool SwiftASTContext::GetCompileUnitImportsImpl(
   if (cu_imports.size() == 0)
     return true;
 
+  // Set PCM validation. This is not a great place to do this, but it
+  // needs to happen after ClangImporter was created and
+  // m_has_explicit_modules has been initialized.
+  {
+    // Read the setting.
+    AutoBool validate_pcm_setting = AutoBool::Auto;
+    TargetSP target_sp = GetTargetWP().lock();
+    if (target_sp)
+      validate_pcm_setting = target_sp->GetSwiftPCMValidation();
+
+    // If the setting is explicit, honor it.
+    bool validate_pcm = validate_pcm_setting != AutoBool::False;
+    if (validate_pcm_setting == AutoBool::Auto) {
+      // Disable validation for explicit modules.
+      validate_pcm = m_has_explicit_modules ? false : true;
+      // Enable validation in asserts builds.
+#ifndef NDEBUG
+      validate_pcm = true;
+#endif
+    }
+    
+    auto &pp_opts = m_clangimporter->getClangPreprocessor()
+      .getPreprocessorOpts();
+    pp_opts.DisablePCHOrModuleValidation =
+        validate_pcm ? clang::DisableValidationForModuleKind::None
+                     : clang::DisableValidationForModuleKind::All;
+    pp_opts.ModulesCheckRelocated = validate_pcm;
+
+    LOG_PRINTF(GetLog(LLDBLog::Types), "PCM validation is %s",
+               validate_pcm ? "disabled" : "enabled");
+  }
+  
   LOG_PRINTF(GetLog(LLDBLog::Types), "Importing dependencies of current CU");
 
   std::string category = "Importing Swift module dependencies for ";

lldb/source/Target/Target.cpp

@@ -4625,6 +4625,13 @@ static constexpr OptionEnumValueElement g_memory_module_load_level_values[] = {
     },
 };
 
+static constexpr OptionEnumValueElement g_swift_pcm_validation_values[] = {
+    {llvm::to_underlying(AutoBool::Auto), "auto",
+     "Turned on when explicit modules are enabled"},
+    {llvm::to_underlying(AutoBool::True), "true", "Enable validation."},
+    {llvm::to_underlying(AutoBool::False), "false", "Disable validation."},
+};
+
 
 #define LLDB_PROPERTIES_target
 #include "TargetProperties.inc"
@@ -4856,6 +4863,19 @@ bool TargetProperties::GetSwiftAllowExplicitModules() const {
   return true;
 }
 
+AutoBool TargetProperties::GetSwiftPCMValidation() const {
+  const Property *exp_property =
+      m_collection_sp->GetPropertyAtIndex(ePropertyExperimental);
+  OptionValueProperties *exp_values =
+      exp_property->GetValue()->GetAsProperties();
+  if (exp_values)
+    return exp_values
+        ->GetPropertyAtIndexAs<AutoBool>(ePropertySwiftPCMValidation)
+      .value_or(AutoBool::Auto);
+
+  return AutoBool::Auto;
+}
+
 Args TargetProperties::GetSwiftPluginServerForPath() const {
   const uint32_t idx = ePropertySwiftPluginServerForPath;
 

lldb/source/Target/TargetProperties.td

@@ -26,6 +26,11 @@ let Definition = "target_experimental" in {
   def SwiftAllowExplicitModules: Property<"swift-allow-explicit-modules", "Boolean">,
     DefaultTrue,
     Desc<"Allows explicit module flags to be passed through to ClangImporter.">;
+  def SwiftPCMValidation: Property<"swift-pcm-validation", "Enum">,
+    Global,
+    DefaultEnumValue<"llvm::to_underlying(AutoBool::Auto)">,
+    EnumValues<"OptionEnumValues(g_swift_pcm_validation_values)">,
+    Desc<"Enable validation when loading Clang PCM files (-fvalidate-pch, -fmodules-check-relocated).">;
 }
 
 let Definition = "target" in {

lldb/test/API/lang/swift/clangimporter/fmodule_flags/TestSwiftFModuleFlags.py

@@ -24,3 +24,4 @@ def test(self):
 #       CHECK-NOT: -fno-implicit-modules
 #       CHECK-NOT: -fno-implicit-module-maps
 #       CHECK: -DMARKER2
+#       CHECK: PCM validation is