[lldb] Redefine p alias to dwim-print command

[kastiglione]

Summary

Redefine the p alias to the dwim-print command instead of expression.

See https://reviews.llvm.org/D138315 for the introduction of dwim-print.

To summarize, dwim-print is, as the name suggests, a command for printing. How a value
gets printed, is decided by dwim-print. In some cases, dwim-print will print values
using the same means as frame variable (because it's generally more reliable and
faster that expression evaluation), and in other cases dwim-print uses the same code
path as expression.

This change has been tested in two different ways:

1. Re-aliasing p to dwim-print, as in this patch
2. Redefinining the expression command to CommandObjectDWIMPrint

Previously, many of the lldb's tests used p, and which meant a test run with p
aliases to dwim-print was a good way to test dwim-print. However most of those tests
were updated to use expression explicitly (in anticipation of this change). Now, the
best way to test dwim-print is the second approach:

diff --git a/lldb/source/Interpreter/CommandInterpreter.cpp b/lldb/source/Interpreter/CommandInterpreter.cpp
index 373c894f34f5..9c943cd30c7c 100644
--- a/lldb/source/Interpreter/CommandInterpreter.cpp
+++ b/lldb/source/Interpreter/CommandInterpreter.cpp
@@ -539,7 +539,7 @@ void CommandInterpreter::LoadCommandDictionary() {
   REGISTER_COMMAND_OBJECT("diagnostics", CommandObjectDiagnostics);
   REGISTER_COMMAND_OBJECT("disassemble", CommandObjectDisassemble);
   REGISTER_COMMAND_OBJECT("dwim-print", CommandObjectDWIMPrint);
-  REGISTER_COMMAND_OBJECT("expression", CommandObjectExpression);
+  REGISTER_COMMAND_OBJECT("expression", CommandObjectDWIMPrint);
   REGISTER_COMMAND_OBJECT("frame", CommandObjectMultiwordFrame);
   REGISTER_COMMAND_OBJECT("gui", CommandObjectGUI);
   REGISTER_COMMAND_OBJECT("help", CommandObjectHelp);

When the test suite is run with this change, there are two main categories of test
failures for specific to features that dwim-print intentionally doesn't support:

1. Top level expressions (--top-level/-p)
2. Multiline expressions

In cases where the behavior of expression is needed, users can use expression at
those times.

[aprantl]

So, one could say that (right now) this patch is NFC for end-users, because dwim-print supports all use-cases that the old p alias supported?

[aprantl]

So from my point of view, this is a good path forward, so assuming that the other reviewers agree, this LGTM.

[kastiglione]

So, one could say that (right now) this patch is NFC for end-users, because dwim-print supports all use-cases that the old p alias supported?

Correct.

lldb/source/Interpreter/CommandInterpreter.cpp

if (cmd_obj_sp)
     AddAlias("file", cmd_obj_sp);
 
   cmd_obj_sp = GetCommandSPExact("target modules");
   if (cmd_obj_sp)
     AddAlias("image", cmd_obj_sp);
 
   alias_arguments_vector_sp = std::make_shared<OptionArgVector>();
 
-  cmd_obj_sp = GetCommandSPExact("expression");
+  cmd_obj_sp = GetCommandSPExact("dwim-print");
   if (cmd_obj_sp) {
     AddAlias("p", cmd_obj_sp, "--")->SetHelpLong("");
     AddAlias("print", cmd_obj_sp, "--")->SetHelpLong("");
-    AddAlias("call", cmd_obj_sp, "--")->SetHelpLong("");
     if (auto *po = AddAlias("po", cmd_obj_sp, "-O --")) {
       po->SetHelp("Evaluate an expression on the current thread.  Displays any "
                   "returned value with formatting "
                   "controlled by the type's author.");
       po->SetHelpLong("");
     }
+  }
+
+  cmd_obj_sp = GetCommandSPExact("expression");
+  if (cmd_obj_sp) {
+    AddAlias("call", cmd_obj_sp, "--")->SetHelpLong("");
     CommandAlias *parray_alias =
         AddAlias("parray", cmd_obj_sp, "--element-count %1 --");
     if (parray_alias) {
         parray_alias->SetHelp
           ("parray <COUNT> <EXPRESSION> -- lldb will evaluate EXPRESSION "
            "to get a typed-pointer-to-an-array in memory, and will display "
            "COUNT elements of that type from the array.");
         parray_alias->SetHelpLong("");