[lldb] Make expect_expr fall back to the dummy target if no target is selected

Summary:

Currently expect_expr will not run the expression if no target is selected. This
patch changes this behavior so that expect_expr will instead fall back to the
dummy target similar to what the `expression` command is doing. This way we
don't have to compile an empty executable to be able to use `expect_expr` (which
is a waste of resources for tests that just test generic type system features).

As a test I modernized the TestTypeOfDeclTypeExpr into a Python test +
expect_expr (as it relied on the dummy target fallback of the expression
command).

Reviewers: labath, JDevlieghere

Reviewed By: labath

Subscribers: abidh

Differential Revision: https://reviews.llvm.org/D83388

lldb/packages/Python/lldbsuite/test/lldbtest.py

@@ -2456,7 +2456,12 @@ FileCheck output:
             options.SetLanguage(frame.GuessLanguage())
             eval_result = self.frame().EvaluateExpression(expr, options)
         else:
-            eval_result = self.target().EvaluateExpression(expr, options)
+            target = self.target()
+            # If there is no selected target, run the expression in the dummy
+            # target.
+            if not target.IsValid():
+                target = self.dbg.GetDummyTarget()
+            eval_result = target.EvaluateExpression(expr, options)
 
         self.assertSuccess(eval_result.GetError())
 

lldb/test/API/lang/cpp/typeof/TestTypeOfDeclTypeExpr.py

@@ -0,0 +1,14 @@
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+class TestCase(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    @no_debug_info_test
+    def test(self):
+        self.expect_expr("int i; __typeof__(i) j = 1; j", result_type="typeof (i)", result_value="1")
+        self.expect_expr("int i; typeof(i) j = 1; j", result_type="typeof (i)", result_value="1")
+        self.expect_expr("int i; decltype(i) j = 1; j", result_type="decltype(i)", result_value="1")

lldb/test/Shell/Expr/TestTypeOfDeclTypeExpr.test

@@ -1,13 +0,0 @@
-# RUN: %lldb -b -s %s | FileCheck %s
-
-expression int i; __typeof__(i) j = 1; j
-# CHECK: (lldb) expression int i; __typeof__(i) j = 1; j
-# CHECK-NEXT: (typeof (i)) {{.*}} = 1
-
-expression int i; typeof(i) j = 1; j
-# CHECK: (lldb) expression int i; typeof(i) j = 1; j
-# CHECK-NEXT: (typeof (i)) {{.*}} = 1
-
-expression int i; decltype(i) j = 1; j
-# CHECK: (lldb) expression int i; decltype(i) j = 1; j
-# CHECK-NEXT: (decltype(i)) {{.*}} = 1