[ADT] Deprecate ArrayRef(std::nullopt)

[kazutakahirata]

Since the use of std::nullopt outside the context of std::optional is
kind of abuse and not intuitive to new comers, this patch deprecates
the constructor. All known uses within the LLVM codebase have been
migrated to other constructors.

[llvmbot]

@llvm/pr-subscribers-llvm-adt

Author: Kazu Hirata (kazutakahirata)

Changes

Since the use of std::nullopt outside the context of std::optional is
kind of abuse and not intuitive to new comers, this patch deprecates
the constructor. All known uses within the LLVM codebase have been
migrated to other constructors.

---

Full diff: https://github.com/llvm/llvm-project/pull/146011.diff

1 Files Affected:

• (modified) llvm/include/llvm/ADT/ArrayRef.h (+1-1)

diff --git a/llvm/include/llvm/ADT/ArrayRef.h b/llvm/include/llvm/ADT/ArrayRef.h
index 892482d64e4a1..7a228d9915cde 100644
--- a/llvm/include/llvm/ADT/ArrayRef.h
+++ b/llvm/include/llvm/ADT/ArrayRef.h
@@ -67,7 +67,7 @@ namespace llvm {
     /*implicit*/ ArrayRef() = default;
 
     /// Construct an empty ArrayRef from std::nullopt.
-    /*implicit*/ ArrayRef(std::nullopt_t) {}
+    /*implicit*/ [[deprecated]] ArrayRef(std::nullopt_t) {}
 
     /// Construct an ArrayRef from a single element.
     /*implicit*/ ArrayRef(const T &OneElt LLVM_LIFETIME_BOUND)

[github-actions]

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

[erichkeane]

This patch missed a few uses in MLIR and CIR as well, so those probably need updating @andykaylor @mmha