[clang] [clang] Add C++26 diagnostics to compatibility diagnosic groups (PR #97806)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Vlad Serebrennikov (Endilll)

<details>
<summary>Changes</summary>

This patch adds `CXXPre26Compat` and `CXXPre26CompatPedantic` groups (which are concerned with new features not available in older language modes) to `CXX98Compat`, etc. This way, if user has `-Wc++20-compat` and they use pack indexing, they will be warned.

Ideally this should have been done when C++26 groups were created, but we shipped two releases of Clang since then.

---
Full diff: https://github.com/llvm/llvm-project/pull/97806.diff


2 Files Affected:

- (modified) clang/docs/ReleaseNotes.rst (+4) 
- (modified) clang/include/clang/Basic/DiagnosticGroups.td (+20-10) 


``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 36cf615a4287c..cf1b529eb7321 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -476,6 +476,10 @@ Modified Compiler Flags
   evaluating to ``true`` and an empty body such as ``while(1);``)
   are considered infinite, even when the ``-ffinite-loop`` flag is set.
 
+- Diagnostics groups about compatibility with a particular C++ Standard version
+  now include dianostics about C++26 features that are not present in older
+  versions.
+
 Removed Compiler Flags
 -------------------------
 
diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 9431eea1f6be2..a4496431e46e4 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -344,7 +344,8 @@ def CXX98Compat : DiagGroup<"c++98-compat",
                              CXXPre14Compat,
                              CXXPre17Compat,
                              CXXPre20Compat,
-                             CXXPre23Compat]>;
+                             CXXPre23Compat,
+                             CXXPre26Compat]>;
 // Warnings for C++11 features which are Extensions in C++98 mode.
 def CXX98CompatPedantic : DiagGroup<"c++98-compat-pedantic",
                                     [CXX98Compat,
@@ -353,7 +354,8 @@ def CXX98CompatPedantic : DiagGroup<"c++98-compat-pedantic",
                                      CXXPre14CompatPedantic,
                                      CXXPre17CompatPedantic,
                                      CXXPre20CompatPedantic,
-                                     CXXPre23CompatPedantic]>;
+                                     CXXPre23CompatPedantic,
+                                     CXXPre26CompatPedantic]>;
 
 def CXX11NarrowingConstReference : DiagGroup<"c++11-narrowing-const-reference">;
 def CXX11Narrowing : DiagGroup<"c++11-narrowing", [CXX11NarrowingConstReference]>;
@@ -384,39 +386,47 @@ def CXX11Compat : DiagGroup<"c++11-compat",
                              CXXPre14Compat,
                              CXXPre17Compat,
                              CXXPre20Compat,
-                             CXXPre23Compat]>;
+                             CXXPre23Compat,
+                             CXXPre26Compat]>;
 def : DiagGroup<"c++0x-compat", [CXX11Compat]>;
 def CXX11CompatPedantic : DiagGroup<"c++11-compat-pedantic",
                                     [CXX11Compat,
                                      CXXPre14CompatPedantic,
                                      CXXPre17CompatPedantic,
                                      CXXPre20CompatPedantic,
-                                     CXXPre23CompatPedantic]>;
+                                     CXXPre23CompatPedantic,
+                                     CXXPre26CompatPedantic]>;
 
 def CXX14Compat : DiagGroup<"c++14-compat", [CXXPre17Compat,
                                              CXXPre20Compat,
-                                             CXXPre23Compat]>;
+                                             CXXPre23Compat,
+                                             CXXPre26Compat]>;
 def CXX14CompatPedantic : DiagGroup<"c++14-compat-pedantic",
                                     [CXX14Compat,
                                      CXXPre17CompatPedantic,
                                      CXXPre20CompatPedantic,
-                                     CXXPre23CompatPedantic]>;
+                                     CXXPre23CompatPedantic,
+                                     CXXPre26CompatPedantic]>;
 
 def CXX17Compat : DiagGroup<"c++17-compat", [DeprecatedRegister,
                                              DeprecatedIncrementBool,
                                              CXX17CompatMangling,
                                              CXXPre20Compat,
-                                             CXXPre23Compat]>;
+                                             CXXPre23Compat,
+                                             CXXPre26Compat]>;
 def CXX17CompatPedantic : DiagGroup<"c++17-compat-pedantic",
                                     [CXX17Compat,
                                      CXXPre20CompatPedantic,
-                                     CXXPre23CompatPedantic]>;
+                                     CXXPre23CompatPedantic,
+                                     CXXPre26CompatPedantic]>;
 def : DiagGroup<"c++1z-compat", [CXX17Compat]>;
 
-def CXX20Compat : DiagGroup<"c++20-compat", [CXXPre23Compat]>;
+def CXX20Compat : DiagGroup<"c++20-compat", [CXXPre23Compat,
+                                             CXXPre26Compat]>;
 def CXX20CompatPedantic : DiagGroup<"c++20-compat-pedantic",
                                     [CXX20Compat,
-                                     CXXPre23CompatPedantic]>;
+                                     CXXPre23CompatPedantic,
+                                     CXXPre26CompatPedantic]>;
 def : DiagGroup<"c++2a-compat", [CXX20Compat]>;
 def : DiagGroup<"c++2a-compat-pedantic", [CXX20CompatPedantic]>;
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/97806