[lldb] Expand background symbol download (#80890)

LLDB has a setting (symbols.enable-background-lookup) that calls
dsymForUUID on a background thread for images as they appear in the
current backtrace. Originally, the laziness of only looking up symbols
for images in the backtrace only existed to bring the number of
dsymForUUID calls down to a manageable number.

Users have requesting the same functionality but blocking. This gives
them the same user experience as enabling dsymForUUID globally, but
without the massive upfront cost of having to download all the images,
the majority of which they'll likely not need.

This patch renames the setting to have a more generic name
(symbols.auto-download) and changes its values from a boolean to an
enum. Users can now specify "off", "background" and "foreground". The
default remains "off" although I'll probably change that in the near
future.

lldb/include/lldb/Core/ModuleList.h

@@ -47,6 +47,26 @@ class UUID;
 class VariableList;
 struct ModuleFunctionSearchOptions;
 
+static constexpr OptionEnumValueElement g_auto_download_enum_values[] = {
+    {
+        lldb::eSymbolDownloadOff,
+        "off",
+        "Disable automatically downloading symbols.",
+    },
+    {
+        lldb::eSymbolDownloadBackground,
+        "background",
+        "Download symbols in the background for images as they appear in the "
+        "backtrace.",
+    },
+    {
+        lldb::eSymbolDownloadForeground,
+        "foreground",
+        "Download symbols in the foreground for images as they appear in the "
+        "backtrace.",
+    },
+};
+
 class ModuleListProperties : public Properties {
   mutable llvm::sys::RWMutex m_symlink_paths_mutex;
   PathMappingList m_symlink_paths;
@@ -60,7 +80,6 @@ public:
   bool SetClangModulesCachePath(const FileSpec &path);
   bool GetEnableExternalLookup() const;
   bool SetEnableExternalLookup(bool new_value);
-  bool GetEnableBackgroundLookup() const;
   bool GetEnableLLDBIndexCache() const;
   bool SetEnableLLDBIndexCache(bool new_value);
   uint64_t GetLLDBIndexCacheMaxByteSize();
@@ -71,6 +90,8 @@ public:
 
   bool GetLoadSymbolOnDemand();
 
+  lldb::SymbolDownload GetSymbolAutoDownload() const;
+
   PathMappingList GetSymlinkMappings() const;
 };
 

lldb/include/lldb/lldb-enumerations.h

@@ -1314,6 +1314,12 @@ enum class ChildCacheState {
               ///< re-use what we computed the last time we called Update.
 };
 
+enum SymbolDownload {
+  eSymbolDownloadOff = 0,
+  eSymbolDownloadBackground = 1,
+  eSymbolDownloadForeground = 2,
+};
+
 } // namespace lldb
 
 #endif // LLDB_LLDB_ENUMERATIONS_H

lldb/source/Core/CoreProperties.td

@@ -8,7 +8,12 @@ let Definition = "modulelist" in {
   def EnableBackgroundLookup: Property<"enable-background-lookup", "Boolean">,
     Global,
     DefaultFalse,
-    Desc<"On macOS, enable calling dsymForUUID (or an equivalent script/binary) in the background to locate symbol files that weren't found.">;
+    Desc<"Alias for backward compatibility: when enabled this is the equivalent to 'symbols.download background'.">;
+  def AutoDownload: Property<"auto-download", "Enum">,
+    Global,
+    DefaultEnumValue<"eSymbolDownloadOff">,
+    EnumValues<"OptionEnumValues(g_auto_download_enum_values)">,
+    Desc<"On macOS, automatically download symbols with dsymForUUID (or an equivalent script/binary) for relevant images in the debug session.">;
   def ClangModulesCachePath: Property<"clang-modules-cache-path", "FileSpec">,
     Global,
     DefaultStringValue<"">,

lldb/source/Core/ModuleList.cpp

@@ -104,10 +104,15 @@ bool ModuleListProperties::SetEnableExternalLookup(bool new_value) {
   return SetPropertyAtIndex(ePropertyEnableExternalLookup, new_value);
 }
 
-bool ModuleListProperties::GetEnableBackgroundLookup() const {
-  const uint32_t idx = ePropertyEnableBackgroundLookup;
-  return GetPropertyAtIndexAs<bool>(
-      idx, g_modulelist_properties[idx].default_uint_value != 0);
+SymbolDownload ModuleListProperties::GetSymbolAutoDownload() const {
+  // Backward compatibility alias.
+  if (GetPropertyAtIndexAs<bool>(ePropertyEnableBackgroundLookup, false))
+    return eSymbolDownloadBackground;
+
+  const uint32_t idx = ePropertyAutoDownload;
+  return GetPropertyAtIndexAs<lldb::SymbolDownload>(
+      idx, static_cast<lldb::SymbolDownload>(
+               g_modulelist_properties[idx].default_uint_value));
 }
 
 FileSpec ModuleListProperties::GetClangModulesCachePath() const {

lldb/source/Host/common/Host.cpp

@@ -550,6 +550,8 @@ llvm::Error Host::OpenFileInExternalEditor(llvm::StringRef editor,
 }
 
 bool Host::IsInteractiveGraphicSession() { return false; }
+
+bool Host::IsNetworkLimited() { return false; }
 #endif
 
 std::unique_ptr<Connection> Host::CreateDefaultConnection(llvm::StringRef url) {

lldb/source/Symbol/SymbolLocator.cpp

@@ -10,6 +10,7 @@
 
 #include "lldb/Core/Debugger.h"
 #include "lldb/Core/PluginManager.h"
+#include "lldb/Host/Host.h"
 
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/Support/ThreadPool.h"
@@ -18,12 +19,10 @@ using namespace lldb;
 using namespace lldb_private;
 
 void SymbolLocator::DownloadSymbolFileAsync(const UUID &uuid) {
-  if (!ModuleList::GetGlobalModuleListProperties().GetEnableBackgroundLookup())
-    return;
-
   static llvm::SmallSet<UUID, 8> g_seen_uuids;
   static std::mutex g_mutex;
-  Debugger::GetThreadPool().async([=]() {
+
+  auto lookup = [=]() {
     {
       std::lock_guard<std::mutex> guard(g_mutex);
       if (g_seen_uuids.count(uuid))
@@ -36,12 +35,23 @@ void SymbolLocator::DownloadSymbolFileAsync(const UUID &uuid) {
     module_spec.GetUUID() = uuid;
     if (!PluginManager::DownloadObjectAndSymbolFile(module_spec, error,
                                                     /*force_lookup=*/true,
-                                                    /*copy_executable=*/false))
+                                                    /*copy_executable=*/true))
       return;
 
     if (error.Fail())
       return;
 
     Debugger::ReportSymbolChange(module_spec);
-  });
+  };
+
+  switch (ModuleList::GetGlobalModuleListProperties().GetSymbolAutoDownload()) {
+  case eSymbolDownloadOff:
+    break;
+  case eSymbolDownloadBackground:
+    Debugger::GetThreadPool().async(lookup);
+    break;
+  case eSymbolDownloadForeground:
+    lookup();
+    break;
+  };
 }