[lldb] Don't print IRForTarget errors directly to the console

[teemperor]

Summary

When we get an error back from IRForTarget we directly print that error to the debugger output
stream instead of putting it in the result object. The result object only gets a vague
"The expression could not be prepared to run in the target" error message that doesn't actually
tell the user what went wrong.

This patch just puts the IRForTarget errors into the status object that is returned to the caller instead
of directly printing it to the debugger. Also updates one test that now can actually check
for the error message it is supposed to check for (instead of the default error which is all we had before).

[JDevlieghere]

Nice

lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionParser.cpp

1330–1331

Drive-by nit: the value doesn't seem used anywhere else and the variable name doesn't add a lot of value, so I'd rewrite this as:

if (!ir_for_target.runOnModule(*execution_unit_sp->GetModule())) {
  ..
}

lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionParser.cpp

execution_unit_sp = std::make_shared<IRExecutionUnit>(
       m_compiler->getTargetOpts().Features);
 
   ClangExpressionHelper *type_system_helper =
       dyn_cast<ClangExpressionHelper>(m_expr.GetTypeSystemHelper());
   ClangExpressionDeclMap *decl_map =
       type_system_helper->DeclMap(); // result can be NULL
 
   if (decl_map) {
-    Target *target = exe_ctx.GetTargetPtr();
-    auto &error_stream = target->GetDebugger().GetErrorStream();
+    StreamString error_stream;
     IRForTarget ir_for_target(decl_map, m_expr.NeedsVariableResolution(),
                               *execution_unit_sp, error_stream,
                               function_name.AsCString());
 
-    bool ir_can_run =
-        ir_for_target.runOnModule(*execution_unit_sp->GetModule());
-
-    if (!ir_can_run) {
-      err.SetErrorString(
-          "The expression could not be prepared to run in the target");
+    if (!ir_for_target.runOnModule(*execution_unit_sp->GetModule())) {
+      err.SetErrorString(error_stream.GetString());
       return err;
     }
 
     Process *process = exe_ctx.GetProcessPtr();
 
     if (execution_policy != eExecutionPolicyAlways &&
         execution_policy != eExecutionPolicyTopLevel) {
       lldb_private::Status interpret_error;

lldb/test/API/lang/objc/modules-non-objc-target/TestObjCModulesNonObjCTarget.py

def test(self):
 
         # Import foundation to get some ObjC types.
         self.expect("expr --lang objc -- @import Foundation")
         # Do something with NSString (which requires special handling when
         # preparing to run in the target). The expression most likely can't
         # be prepared to run in the target but it should at least not crash LLDB.
         self.expect('expr --lang objc -- [NSString stringWithFormat:@"%d", 1];',
                     error=True,
-                    substrs=["error: The expression could not be prepared to run in the target"])
+                    substrs=["Rewriting an Objective-C constant string requires CFStringCreateWithBytes"])