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

Michael137 · 2025-02-12T12:33:00Z

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

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

llvmbot · 2025-02-12T12:33:44Z

@llvm/pr-subscribers-lldb

Author: Michael Buch (Michael137)

Changes

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

Full diff: https://github.com/llvm/llvm-project/pull/126901.diff

8 Files Affected:

(modified) lldb/include/lldb/API/SBTarget.h (+1)
(modified) lldb/include/lldb/API/SBType.h (+7)
(modified) lldb/include/lldb/API/SBValue.h (+1)
(modified) lldb/source/API/SBType.cpp (+34)
(modified) lldb/test/API/lang/cpp/class-template-parameter-pack/TestTemplatePackArgs.py (+17-2)
(modified) lldb/test/API/lang/cpp/template-arguments/Makefile (+1)
(modified) lldb/test/API/lang/cpp/template-arguments/TestCppTemplateArguments.py (+30-2)
(modified) lldb/test/API/lang/cpp/template-arguments/main.cpp (+5)

diff --git a/lldb/include/lldb/API/SBTarget.h b/lldb/include/lldb/API/SBTarget.h
index 9b97359d49cf9..bb912ab41d0fe 100644
--- a/lldb/include/lldb/API/SBTarget.h
+++ b/lldb/include/lldb/API/SBTarget.h
@@ -964,6 +964,7 @@ class LLDB_API SBTarget {
   friend class SBSection;
   friend class SBSourceManager;
   friend class SBSymbol;
+  friend class SBType;
   friend class SBTypeStaticField;
   friend class SBValue;
   friend class SBVariablesOptions;
diff --git a/lldb/include/lldb/API/SBType.h b/lldb/include/lldb/API/SBType.h
index 63ba91082d576..9ad3244686328 100644
--- a/lldb/include/lldb/API/SBType.h
+++ b/lldb/include/lldb/API/SBType.h
@@ -221,6 +221,13 @@ class SBType {
 
   lldb::SBType GetTemplateArgumentType(uint32_t idx);
 
+  /// Returns the value of the non-type template parameter at index \c idx.
+  /// If \c idx is out-of-bounds or the template parameter doesn't have
+  /// a value, returns an empty SBValue.
+  ///
+  /// This function will expand parameter packs.
+  lldb::SBValue GetTemplateArgumentValue(lldb::SBTarget target, uint32_t idx);
+
   /// Return the TemplateArgumentKind of the template argument at index idx.
   /// Variadic argument packs are automatically expanded.
   lldb::TemplateArgumentKind GetTemplateArgumentKind(uint32_t idx);
diff --git a/lldb/include/lldb/API/SBValue.h b/lldb/include/lldb/API/SBValue.h
index 9090cece80f7c..46ef6daa95264 100644
--- a/lldb/include/lldb/API/SBValue.h
+++ b/lldb/include/lldb/API/SBValue.h
@@ -446,6 +446,7 @@ class LLDB_API SBValue {
   friend class SBModule;
   friend class SBTarget;
   friend class SBThread;
+  friend class SBType;
   friend class SBTypeStaticField;
   friend class SBTypeSummary;
   friend class SBValueList;
diff --git a/lldb/source/API/SBType.cpp b/lldb/source/API/SBType.cpp
index 4cc16c64e4756..8d04e9650b781 100644
--- a/lldb/source/API/SBType.cpp
+++ b/lldb/source/API/SBType.cpp
@@ -687,6 +687,40 @@ lldb::TemplateArgumentKind SBType::GetTemplateArgumentKind(uint32_t idx) {
   return eTemplateArgumentKindNull;
 }
 
+lldb::SBValue SBType::GetTemplateArgumentValue(lldb::SBTarget target,
+                                               uint32_t idx) {
+  LLDB_INSTRUMENT_VA(this, target, idx);
+
+  if (!IsValid())
+    return SBValue();
+
+  std::optional<CompilerType::IntegralTemplateArgument> arg;
+  const bool expand_pack = true;
+  switch (GetTemplateArgumentKind(idx)) {
+  case eTemplateArgumentKindIntegral:
+    arg = m_opaque_sp->GetCompilerType(false).GetIntegralTemplateArgument(
+        idx, expand_pack);
+    break;
+  default:
+    break;
+  }
+
+  if (!arg)
+    return {};
+
+  Scalar value{arg->value};
+
+  if (!value.IsValid())
+    return {};
+
+  DataExtractor data;
+  value.GetData(data);
+
+  auto value_obj_sp = ValueObjectConstResult::Create(
+      target.GetSP().get(), arg->type, ConstString("value"), data);
+  return SBValue(std::move(value_obj_sp));
+}
+
 SBType SBType::FindDirectNestedType(const char *name) {
   LLDB_INSTRUMENT_VA(this, name);
 
diff --git a/lldb/test/API/lang/cpp/class-template-parameter-pack/TestTemplatePackArgs.py b/lldb/test/API/lang/cpp/class-template-parameter-pack/TestTemplatePackArgs.py
index c571357ff6720..f2467cbea9439 100644
--- a/lldb/test/API/lang/cpp/class-template-parameter-pack/TestTemplatePackArgs.py
+++ b/lldb/test/API/lang/cpp/class-template-parameter-pack/TestTemplatePackArgs.py
@@ -11,7 +11,7 @@
 class TemplatePackArgsTestCase(TestBase):
     def test_template_argument_pack(self):
         self.build()
-        (_, _, thread, _) = lldbutil.run_to_source_breakpoint(
+        (target, _, thread, _) = lldbutil.run_to_source_breakpoint(
             self, "breakpoint here", lldb.SBFileSpec("main.cpp"), exe_name="a.out"
         )
         frame = thread.GetSelectedFrame()
@@ -33,10 +33,25 @@ def test_template_argument_pack(self):
         self.assertEqual(
             only_pack.GetType().GetTemplateArgumentType(2).GetName(), "double"
         )
-        # Access the C<double, 42> template parameter.
+
         nested_template = only_pack.GetType().GetTemplateArgumentType(3)
         self.assertEqual(nested_template.GetName(), "D<int, int, bool>")
         self.assertEqual(nested_template.GetNumberOfTemplateArguments(), 3)
         self.assertEqual(nested_template.GetTemplateArgumentType(0).GetName(), "int")
         self.assertEqual(nested_template.GetTemplateArgumentType(1).GetName(), "int")
         self.assertEqual(nested_template.GetTemplateArgumentType(2).GetName(), "bool")
+
+        my_c = frame.FindVariable("myC")
+        self.assertTrue(my_c.IsValid(), "make sure we find the myC variable")
+
+        # Out of bounds index.
+        self.assertFalse(my_c.GetType().GetTemplateArgumentValue(target, 3))
+
+        # Out of bounds index.
+        template_param_value = my_c.GetType().GetTemplateArgumentValue(target, 1)
+        self.assertEqual(template_param_value.GetTypeName(), "int")
+        self.assertEqual(template_param_value.GetValueAsSigned(), 16)
+
+        template_param_value = my_c.GetType().GetTemplateArgumentValue(target, 2)
+        self.assertEqual(template_param_value.GetTypeName(), "int")
+        self.assertEqual(template_param_value.GetValueAsSigned(), 32)
diff --git a/lldb/test/API/lang/cpp/template-arguments/Makefile b/lldb/test/API/lang/cpp/template-arguments/Makefile
index 99998b20bcb05..4f79c0a900c3a 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 7b63a6cca8db4..eb5959c2a3668 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 +27,38 @@ def test(self):
         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>")
+        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 728bd400c2586..0c0eb97cbc858 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() {}

Michael137 · 2025-02-12T12:35:03Z

We now have three APIs to query template parameters: GetTemplateParameterType/GetTemplateParameterKind/GetTemplateParameterValue. Perhaps we could just represent a template parameter as an SBValue instead? And return that via a SBType::GetTemplateParameter. Then the type/kind/name/value can be queried off of it?

I chose the simpler approach with this patch but happy to reconsider if others feel one way or the other

Michael137 · 2025-02-12T12:36:03Z

lldb/include/lldb/API/SBTarget.h

@@ -964,6 +964,7 @@ class LLDB_API SBTarget {
  friend class SBSection;
  friend class SBSourceManager;
  friend class SBSymbol;
+  friend class SBType;


This was only necessary to get access to SBTarget::GetSP

This is completely optional, it just seemed like a good opportunity to advertise my idea for avoiding these random criss-cross friend declarations.

Okay, sorry, this is my bad. I didn't mean to imply that it should be done in this patch. I do like this idea, but I think that if we do that, it should be done in a more wider fashion rather than a one-off.

Ah fair enough, reverted that for now

github-actions · 2025-02-12T12:36:31Z

✅ With the latest revision this PR passed the Python code formatter.

Michael137 · 2025-02-12T12:39:04Z

lldb/include/lldb/API/SBValue.h

@@ -446,6 +446,7 @@ class LLDB_API SBValue {
  friend class SBModule;
  friend class SBTarget;
  friend class SBThread;
+  friend class SBType;


This was necessary to get access to the SBValue constructor

labath

Perhaps we could just represent a template parameter as an SBValue instead?

I'm not sure I understand. Do you mean, even for type template template parameters? How would that work? By creating an empty value of the given type? And how would we pass the "kind" of the template parameter? I don't think it makes sense adding it to the SBValue class..

The current implementation seems okay to me, but if we wanted to create something fancier, then I think it'd be best to create a new SB class (SBTypeTemplateParameter?)

labath · 2025-02-12T12:45:42Z

lldb/source/API/SBType.cpp

+  DataExtractor data;
+  value.GetData(data);
+
+  return SBValue(ValueObjectConstResult::Create(target.GetSP().get(), arg->type,


How about ValueObject::CreateValueObjectFromData ? It looks like it calls the same function underneath, but it seem more correct.

labath · 2025-02-12T12:46:57Z

lldb/source/API/SBType.cpp

+
+  Scalar value{arg->value};
+
+  if (!value.IsValid())


Can this ever be not valid? What would that even mean?

Yea we don't need this

labath · 2025-02-12T12:55:48Z

lldb/include/lldb/API/SBTarget.h

@@ -964,6 +964,7 @@ class LLDB_API SBTarget {
  friend class SBSection;
  friend class SBSourceManager;
  friend class SBSymbol;
+  friend class SBType;


This is completely optional, it just seemed like a good opportunity to advertise my idea for avoiding these random criss-cross friend declarations.

Michael137 · 2025-02-12T13:08:20Z

Perhaps we could just represent a template parameter as an SBValue instead?

I'm not sure I understand. Do you mean, even for type template template parameters? How would that work? By creating an empty value of the given type? And how would we pass the "kind" of the template parameter? I don't think it makes sense adding it to the SBValue class..

The current implementation seems okay to me, but if we wanted to create something fancier, then I think it'd be best to create a new SB class (SBTypeTemplateParameter?)

Yea SBTypeTemplateParameter was more along the lines of what I was thinking, if we wanted to unify these APIs

… Scalar::IsValid check

Michael137 · 2025-02-12T13:42:08Z

This is completely optional, it just seemed like a good opportunity to advertise my idea for avoiding these random criss-cross friend declarations.

Tried it, let me know if this is what you were imagining or not

github-actions · 2025-02-12T13:44:43Z

✅ With the latest revision this PR passed the C/C++ code formatter.

labath

This looks okay to me (modulo the friend messup). Given this is a public API and whatnot, it might be a good idea to wait if folks in the US have any thoughts on this.

medismailben

LGTM!

) 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 (cherry picked from commit 3ad8657)

) 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

) 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 (cherry picked from commit 3ad8657)

…to-6.1 [lldb][SBAPI] Add new SBType::GetTemplateParameterValue API (llvm#126901)

Michael137 requested review from labath, medismailben and jimingham February 12, 2025 12:33

Michael137 requested a review from JDevlieghere as a code owner February 12, 2025 12:33

llvmbot added the lldb label Feb 12, 2025

Michael137 commented Feb 12, 2025

View reviewed changes

fixup! formatting

09205d7

labath reviewed Feb 12, 2025

View reviewed changes

fixup! use CreateValueObjectFromData; add test-case; remove redundant…

2ff8278

… Scalar::IsValid check

labath approved these changes Feb 12, 2025

View reviewed changes

Michael137 force-pushed the lldb/template-arg-value-api branch from 6a2c0d3 to 2ff8278 Compare February 12, 2025 15:29

medismailben approved these changes Feb 12, 2025

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Michael137 merged commit 3ad8657 into llvm:main Feb 13, 2025
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Michael137 deleted the lldb/template-arg-value-api branch February 13, 2025 09:53

adrian-prantl added a commit to swiftlang/llvm-project that referenced this pull request Feb 14, 2025

Merge pull request #10020 from swiftlang/lldb/template-arg-value-api-…

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…to-6.1 [lldb][SBAPI] Add new SBType::GetTemplateParameterValue API (llvm#126901)

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

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

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