[clang] [llvm] [mlir] [ADT] Deprecate MutableArrayRef(std::nullopt) (PR #146113)

[Kazu Hirata via llvm-commits]

https://github.com/kazutakahirata created https://github.com/llvm/llvm-project/pull/146113

ArrayRef(std::nullopt) just got deprecated.  This patch does the same
to MutableArrayRef(std::nullopt).  Since there are only a couple of
uses, this patch does migration and deprecation at the same time.


>From 5fae8431a310e14bbfad65d61ef2fec8b4ed10e7 Mon Sep 17 00:00:00 2001
From: Kazu Hirata <kazu at google.com>
Date: Fri, 27 Jun 2025 01:13:00 -0700
Subject: [PATCH] [ADT] Deprecate MutableArrayRef(std::nullopt)

ArrayRef(std::nullopt) just got deprecated.  This patch does the same
to MutableArrayRef(std::nullopt).  Since there are only a couple of
uses, this patch does migration and deprecation at the same time.
---
 clang/lib/Serialization/ASTWriterDecl.cpp | 2 +-
 llvm/include/llvm/ADT/ArrayRef.h          | 3 ++-
 mlir/lib/IR/Diagnostics.cpp               | 2 +-
 3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index 2e390dbe79ec6..7457c4920dd10 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -302,7 +302,7 @@ namespace clang {
     }
     MutableArrayRef<FunctionTemplateSpecializationInfo>
     getPartialSpecializations(FunctionTemplateDecl::Common *) {
-      return std::nullopt;
+      return {};
     }
 
     template<typename DeclTy>
diff --git a/llvm/include/llvm/ADT/ArrayRef.h b/llvm/include/llvm/ADT/ArrayRef.h
index 3b05cfb326c82..247975cc2fb12 100644
--- a/llvm/include/llvm/ADT/ArrayRef.h
+++ b/llvm/include/llvm/ADT/ArrayRef.h
@@ -304,7 +304,8 @@ namespace llvm {
     /*implicit*/ MutableArrayRef() = default;
 
     /// Construct an empty MutableArrayRef from std::nullopt.
-    /*implicit*/ MutableArrayRef(std::nullopt_t) : ArrayRef<T>() {}
+    /*implicit*/ LLVM_DEPRECATED("Use {} or MutableArrayRef<T>() instead", "{}")
+    MutableArrayRef(std::nullopt_t) : ArrayRef<T>() {}
 
     /// Construct a MutableArrayRef from a single element.
     /*implicit*/ MutableArrayRef(T &OneElt) : ArrayRef<T>(OneElt) {}
diff --git a/mlir/lib/IR/Diagnostics.cpp b/mlir/lib/IR/Diagnostics.cpp
index 3a0f81d240336..3e337951bcd3f 100644
--- a/mlir/lib/IR/Diagnostics.cpp
+++ b/mlir/lib/IR/Diagnostics.cpp
@@ -727,7 +727,7 @@ SourceMgrDiagnosticVerifierHandlerImpl::computeExpectedDiags(
     raw_ostream &os, llvm::SourceMgr &mgr, const llvm::MemoryBuffer *buf) {
   // If the buffer is invalid, return an empty list.
   if (!buf)
-    return std::nullopt;
+    return {};
   auto &expectedDiags = expectedDiagsPerFile[buf->getBufferIdentifier()];
 
   // The number of the last line that did not correlate to a designator.