[llvm] [llvm] replace static_assert with std::enable_if_t in ilist_node_impl (PR #127722)

[Andrew Rogers via llvm-commits]

https://github.com/andrurogerz updated https://github.com/llvm/llvm-project/pull/127722

>From 28224ca715b4a7370152099303e0e6e674220500 Mon Sep 17 00:00:00 2001
From: Andrew Rogers <andrurogerz at gmail.com>
Date: Tue, 18 Feb 2025 14:45:43 -0800
Subject: [PATCH 1/4] replace static_assert with std::enable_if_t

---
 llvm/include/llvm/ADT/ilist_node.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/llvm/include/llvm/ADT/ilist_node.h b/llvm/include/llvm/ADT/ilist_node.h
index bfd50f8b3fb71..2148d6fde9be0 100644
--- a/llvm/include/llvm/ADT/ilist_node.h
+++ b/llvm/include/llvm/ADT/ilist_node.h
@@ -18,6 +18,8 @@
 #include "llvm/ADT/ilist_node_base.h"
 #include "llvm/ADT/ilist_node_options.h"
 
+#include <type_traits>
+
 namespace llvm {
 
 namespace ilist_detail {
@@ -147,9 +149,8 @@ class ilist_node_impl
   ///
   /// This requires sentinel tracking to be explicitly enabled.  Use the
   /// ilist_sentinel_tracking<true> option to get this API.
+  template <typename = std::enable_if_t<OptionsT::is_sentinel_tracking_explicit>>
   bool isSentinel() const {
-    static_assert(OptionsT::is_sentinel_tracking_explicit,
-                  "Use ilist_sentinel_tracking<true> to enable isSentinel()");
     return node_base_type::isSentinel();
   }
 };

>From 31544b68bedbfc4e52ea90e9e362bbe0dc09cc0c Mon Sep 17 00:00:00 2001
From: Andrew Rogers <andrurogerz at gmail.com>
Date: Tue, 18 Feb 2025 16:02:57 -0800
Subject: [PATCH 2/4] clang-format

---
 llvm/include/llvm/ADT/ilist_node.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/llvm/include/llvm/ADT/ilist_node.h b/llvm/include/llvm/ADT/ilist_node.h
index 2148d6fde9be0..8b3bc8ce50aa2 100644
--- a/llvm/include/llvm/ADT/ilist_node.h
+++ b/llvm/include/llvm/ADT/ilist_node.h
@@ -149,7 +149,8 @@ class ilist_node_impl
   ///
   /// This requires sentinel tracking to be explicitly enabled.  Use the
   /// ilist_sentinel_tracking<true> option to get this API.
-  template <typename = std::enable_if_t<OptionsT::is_sentinel_tracking_explicit>>
+  template <
+      typename = std::enable_if_t<OptionsT::is_sentinel_tracking_explicit>>
   bool isSentinel() const {
     return node_base_type::isSentinel();
   }

>From 30da81deb9725509bf9ee296aa1bd84b3314acd9 Mon Sep 17 00:00:00 2001
From: Andrew Rogers <andrurogerz at gmail.com>
Date: Tue, 18 Feb 2025 18:10:36 -0800
Subject: [PATCH 3/4] use std::enable_if_t for the return type to compile
 properly with clang

---
 llvm/include/llvm/ADT/ilist_node.h | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/llvm/include/llvm/ADT/ilist_node.h b/llvm/include/llvm/ADT/ilist_node.h
index 8b3bc8ce50aa2..a23f00613c2a3 100644
--- a/llvm/include/llvm/ADT/ilist_node.h
+++ b/llvm/include/llvm/ADT/ilist_node.h
@@ -149,9 +149,8 @@ class ilist_node_impl
   ///
   /// This requires sentinel tracking to be explicitly enabled.  Use the
   /// ilist_sentinel_tracking<true> option to get this API.
-  template <
-      typename = std::enable_if_t<OptionsT::is_sentinel_tracking_explicit>>
-  bool isSentinel() const {
+  template <typename T = OptionsT>
+  std::enable_if_t<T::is_sentinel_tracking_explicit, bool> isSentinel() const {
     return node_base_type::isSentinel();
   }
 };

>From 00ea38992441cdd65c23bcc6af2bc38e3f934f86 Mon Sep 17 00:00:00 2001
From: Andrew Rogers <andrurogerz at gmail.com>
Date: Wed, 19 Feb 2025 09:53:10 -0800
Subject: [PATCH 4/4] add a comment explainin why std::enable_if is used on
 this method

---
 llvm/include/llvm/ADT/ilist_node.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/llvm/include/llvm/ADT/ilist_node.h b/llvm/include/llvm/ADT/ilist_node.h
index a23f00613c2a3..67384546a9275 100644
--- a/llvm/include/llvm/ADT/ilist_node.h
+++ b/llvm/include/llvm/ADT/ilist_node.h
@@ -149,6 +149,11 @@ class ilist_node_impl
   ///
   /// This requires sentinel tracking to be explicitly enabled.  Use the
   /// ilist_sentinel_tracking<true> option to get this API.
+  ///
+  /// Rather than using static_assert to enforce the API is not called when
+  /// configured with is_sentinel_tracking_explicit=false, the method is
+  /// conditionally provided using std::enable_if.  This way, clients of
+  /// ilist_node_impl can be fully instantiated for DLLExport on Windows.
   template <typename T = OptionsT>
   std::enable_if_t<T::is_sentinel_tracking_explicit, bool> isSentinel() const {
     return node_base_type::isSentinel();