[lldb] Initialize a shared, blank SwiftASTContext in Objective-C frames

The result of an Objective-C expression can be a Swift
ValueObject. This means that `po foo` in Objective-C may run a Swift
expression to print the object description of the result of the
Objective-C expression `foo`. That expression has very few
dependencies:

```
Swift._DebuggerSupport.stringForPrintObject(Swift.unsafeBitCast(0x001234, to: AnyObject.self))
```

To avoid scanning potentially incompatible compiler flags and/or doing
implicit imports in anotherwise explicitly built project, this patch
ensures that one SwiftASTContext per triple is created, with no other
contextual information. This makes `po` in ObjC much faster and
reliable, the downside of this is that

```expr -l Swift -- import ModuleName```

will only work reliably for SDK modules outside of Swift frames.

rdar://153332037

Author: adrian-prantl

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

@@ -2707,17 +2707,18 @@ SwiftASTContext::CreateInstance(const SymbolContext &sc,
 
   CompileUnit *cu = sc.comp_unit;
   const char *key = TypeSystemSwiftTypeRef::DeriveKeyFor(sc);
+  bool swift_context = cu && cu->GetLanguage() == eLanguageTypeSwift;
   std::string m_description;
   {
     StreamString ss;
     ss << "SwiftASTContext";
     if (for_expressions)
       ss << "ForExpressions";
     ss << "(module: " << '"' << key << "\", " << "cu: " << '"';
-    if (cu)
+    if (cu && swift_context)
       ss << cu->GetPrimaryFile().GetFilename();
     else
-      ss << "null";
+      ss << "*";
     ss << '"' << ')';
     m_description = ss.GetString();
   }
@@ -2797,7 +2798,8 @@ SwiftASTContext::CreateInstance(const SymbolContext &sc,
   ModuleList module_module;
   if (!target_sp)
     module_module.Append(module_sp);
-  ModuleList &modules = target_sp ? target_sp->GetImages() : module_module;
+  ModuleList &modules =
+      (target_sp && swift_context) ? target_sp->GetImages() : module_module;
   const size_t num_images = modules.GetSize();
 
   // Set the SDK path prior to doing search paths.  Otherwise when we
@@ -3133,7 +3135,8 @@ SwiftASTContext::CreateInstance(const SymbolContext &sc,
           }
         }
       };
-  scan_module(module_sp, 0);
+  if (swift_context)
+    scan_module(module_sp, 0);
   for (size_t mi = 0; mi != num_images; ++mi) {
     auto image_sp = modules.GetModuleAtIndex(mi);
     if (!visited_modules.count(image_sp.get()))

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

@@ -2072,15 +2072,14 @@ ConstString TypeSystemSwiftTypeRef::GetSwiftModuleFor(const SymbolContext &sc) {
 }
 
 const char *TypeSystemSwiftTypeRef::DeriveKeyFor(const SymbolContext &sc) {
-  if (sc.function)
+  if (sc.comp_unit && sc.comp_unit->GetLanguage() == eLanguageTypeSwift)
     if (ConstString name = GetSwiftModuleFor(sc))
       return name.GetCString();
 
-  if (sc.module_sp) {
-    if (sc.module_sp->GetFileSpec())
-      return sc.module_sp->GetFileSpec().GetFilename().GetCString();
-    return sc.module_sp->GetObjectName().GetCString();
-  }
+  // Otherwise create a catch-all context per unique triple.
+  if (sc.module_sp)
+    return ConstString(sc.module_sp->GetArchitecture().GetTriple().str()).AsCString();
+
   return nullptr;
 }
 
@@ -2563,6 +2562,9 @@ template <> bool Equivalent<CompilerType>(CompilerType l, CompilerType r) {
   ConstString rhs = r.GetMangledTypeName();
   if (lhs == ConstString("$sSiD") && rhs == ConstString("$sSuD"))
     return true;
+  if (lhs.GetStringRef() == "$sSPySo0023unnamedstruct_hEEEdhdEaVGSgD" &&
+      rhs.GetStringRef() == "$ss13OpaquePointerVSgD")
+    return true;
   // Ignore missing sugar.
   swift::Demangle::Demangler dem;
   auto l_node = GetDemangledType(dem, lhs.GetStringRef());

lldb/test/API/lang/swift/po/objc/Base.h

@@ -0,0 +1,3 @@
+@import Foundation;
+@interface Base : NSObject
+@end

lldb/test/API/lang/swift/po/objc/Foo.swift

@@ -0,0 +1,15 @@
+import Foundation
+import Base
+
+private class Bar : Base {
+}
+
+extension Bar {
+  override var debugDescription : String { "Hello from Swift" }
+}
+
+@objc public class Foo : NSObject {
+  @objc public func getBase() -> Base? {
+    return Bar()
+  }
+}

lldb/test/API/lang/swift/po/objc/Makefile

@@ -0,0 +1,9 @@
+OBJC_SOURCES := main.m
+CFLAGS_EXTRAS = $(MANDATORY_MODULE_BUILD_CFLAGS) -I. -I$(BUILDDIR)
+
+SWIFT_SOURCES := Foo.swift
+SWIFTFLAGS_EXTRAS = -Xcc -I$(SRCDIR) -emit-objc-header-path Foo.h -parse-as-library
+
+all: Foo.swift.o $(EXE)
+
+include Makefile.rules

lldb/test/API/lang/swift/po/objc/TestSwiftPOObjC.py

@@ -0,0 +1,27 @@
+import lldb
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test.decorators import *
+import lldbsuite.test.lldbutil as lldbutil
+
+class TestSwiftPOObjC(TestBase):
+    #NO_DEBUG_INFO_TESTCASE = True
+    @skipUnlessDarwin
+    @swiftTest
+    def test(self):
+        """Test running po on a Swift object from Objective-C. This
+        should initialize a generic SwiftASTContext with no parsing of
+        Swift modules happening"""
+        self.build()
+
+        lldbutil.run_to_source_breakpoint(
+            self, "break here", lldb.SBFileSpec('main.m'))
+
+        log = self.getBuildArtifact("types.log")
+        self.expect('log enable lldb types -f "%s"' % log)
+        self.expect("expr -O -- base", substrs=["Hello from Swift"])
+        self.filecheck('platform shell cat "%s"' % log, __file__)
+### -cc1 should be round-tripped so there is no more `-cc1` in the extra args. Look for `-triple` which is a cc1 flag.
+#       CHECK-NOT: parsed module "a"
+#       CHECK:  SwiftASTContextForExpressions(module: "{{.*-.*-.*}}", cu: "*")::LogConfiguration()
+        self.expect("expr -- base", substrs=["a.Bar"])
+        self.expect("expr -- *base", substrs=["a.Bar"])

lldb/test/API/lang/swift/po/objc/main.m

@@ -0,0 +1,13 @@
+@import Foundation;
+@import Base;
+#import "Foo.h"
+
+@implementation Base
+@end
+
+int main(int argc, char **argv) {
+  Foo *foo = [[Foo alloc] init];
+  Base *base = [foo getBase];
+  return 0; // break here
+
+}

lldb/test/API/lang/swift/po/objc/module.modulemap

@@ -0,0 +1 @@
+module Base { header "Base.h" }