[lldb][SBAPI] Add new SBType::GetTemplateParameterValue API (#126901)

This patch adds a new API to `SBType` to retrieve the value of a
template parameter given an index. We re-use the
`TypeSystemClang::GetIntegralTemplateArgument` for this and thus
currently only supports integral non-type template parameters. Types
like float/double are not supported yet.

rdar://144395216

3 files changed, 40 insertions, 2 deletions

diff --git a/lldb/test/API/lang/cpp/template-arguments/Makefile b/lldb/test/API/lang/cpp/template-arguments/Makefile
index 99998b20bcb0..4f79c0a900c3 100644
--- a/lldb/test/API/lang/cpp/template-arguments/Makefile
+++ b/lldb/test/API/lang/cpp/template-arguments/Makefile
@@ -1,3 +1,4 @@
 CXX_SOURCES := main.cpp
+CXXFLAGS_EXTRAS := -std=c++20
 
 include Makefile.rules
diff --git a/lldb/test/API/lang/cpp/template-arguments/TestCppTemplateArguments.py b/lldb/test/API/lang/cpp/template-arguments/TestCppTemplateArguments.py
index 7b63a6cca8db..f1b3d7a9806f 100644
--- a/lldb/test/API/lang/cpp/template-arguments/TestCppTemplateArguments.py
+++ b/lldb/test/API/lang/cpp/template-arguments/TestCppTemplateArguments.py
@@ -8,7 +8,7 @@ class TestCase(TestBase):
     @no_debug_info_test
     def test(self):
         self.build()
-        self.dbg.CreateTarget(self.getBuildArtifact("a.out"))
+        target = self.dbg.CreateTarget(self.getBuildArtifact("a.out"))
 
         value = self.expect_expr("temp1", result_type="C<int, 2>")
         template_type = value.GetType()
@@ -27,10 +27,42 @@ class TestCase(TestBase):
         self.assertEqual(
             template_type.GetTemplateArgumentType(1).GetName(), "unsigned int"
         )
-        # FIXME: There is no way to get the actual value of the parameter.
+
+        # Template parameter isn't a NTTP.
+        self.assertFalse(template_type.GetTemplateArgumentValue(target, 0))
+
+        # Template parameter index out-of-bounds.
+        self.assertFalse(template_type.GetTemplateArgumentValue(target, 2))
+
+        # Template parameter is a NTTP.
+        param_val = template_type.GetTemplateArgumentValue(target, 1)
+        self.assertEqual(param_val.GetTypeName(), "unsigned int")
+        self.assertEqual(param_val.GetValueAsUnsigned(), 2)
 
         # Try to get an invalid template argument.
         self.assertEqual(
             template_type.GetTemplateArgumentKind(2), lldb.eTemplateArgumentKindNull
         )
         self.assertEqual(template_type.GetTemplateArgumentType(2).GetName(), "")
+
+        value = self.expect_expr("temp2", result_type="Foo<short, -2>")
+
+        # Can't get template parameter value with invalid target.
+        self.assertFalse(value.GetType().GetTemplateArgumentValue(lldb.SBTarget(), 1))
+
+        template_param_value = value.GetType().GetTemplateArgumentValue(target, 1)
+        self.assertTrue(template_param_value)
+        self.assertEqual(template_param_value.GetTypeName(), "short")
+        self.assertEqual(template_param_value.GetValueAsSigned(), -2)
+
+        value = self.expect_expr("temp3", result_type="Foo<char, 'v'>")
+        template_param_value = value.GetType().GetTemplateArgumentValue(target, 1)
+        self.assertTrue(template_param_value)
+        self.assertEqual(template_param_value.GetTypeName(), "char")
+        self.assertEqual(chr(template_param_value.GetValueAsSigned()), "v")
+
+        # FIXME: type should be Foo<float, 2.0f>
+        # FIXME: double/float NTTP parameter values currently not supported.
+        value = self.expect_expr("temp4", result_type="Foo<float, float>")
+        template_param_value = value.GetType().GetTemplateArgumentValue(target, 1)
+        self.assertFalse(template_param_value)
diff --git a/lldb/test/API/lang/cpp/template-arguments/main.cpp b/lldb/test/API/lang/cpp/template-arguments/main.cpp
index 728bd400c258..0c0eb97cbc85 100644
--- a/lldb/test/API/lang/cpp/template-arguments/main.cpp
+++ b/lldb/test/API/lang/cpp/template-arguments/main.cpp
@@ -5,4 +5,9 @@ struct C {
 
 C<int, 2> temp1;
 
+template <typename T, T value> struct Foo {};
+Foo<short, -2> temp2;
+Foo<char, 'v'> temp3;
+Foo<float, 2.0f> temp4;
+
 int main() {}