[llvm] [LLVM][CodingStandard] Extend namespace qualifier rule to variables (PR #163588)

[Rahul Joshi via llvm-commits]

https://github.com/jurahul updated https://github.com/llvm/llvm-project/pull/163588

>From b75122e8a543031f09d693270af5a6032e69ffd0 Mon Sep 17 00:00:00 2001
From: Rahul Joshi <rjoshi at nvidia.com>
Date: Wed, 15 Oct 2025 09:36:26 -0700
Subject: [PATCH 1/3] [LLVM][CodingStandard] Extend namespace qualifier rule to
 variables

Extend CS rule to use namespace qialifiers to define previously
declared functions to variables as well.
---
 llvm/docs/CodingStandards.rst | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/llvm/docs/CodingStandards.rst b/llvm/docs/CodingStandards.rst
index 65dd794103ac3..128892edf0772 100644
--- a/llvm/docs/CodingStandards.rst
+++ b/llvm/docs/CodingStandards.rst
@@ -860,23 +860,28 @@ your private interface remains private and undisturbed by outsiders.
     It's okay to put extra implementation methods in a public class itself. Just
     make them private (or protected) and all is well.
 
-Use Namespace Qualifiers to Implement Previously Declared Functions
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Use Namespace Qualifiers to Define Previously Declared Variables and Functions
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-When providing an out-of-line implementation of a function in a source file, do
-not open namespace blocks in the source file. Instead, use namespace qualifiers
-to help ensure that your definition matches an existing declaration. Do this:
+When providing an out-of-line definition of a variable or a function in a source
+file, do not open namespace blocks in the source file. Instead, use namespace
+qualifiers to help ensure that your definition matches an existing declaration.
+Do this:
 
 .. code-block:: c++
 
   // Foo.h
   namespace llvm {
+  extern int FooVal;
   int foo(const char *s);
   }
 
   // Foo.cpp
   #include "Foo.h"
   using namespace llvm;
+
+  int llvm::FooVal;
+
   int llvm::foo(const char *s) {
     // ...
   }

>From d8c19ec4760344a356af67ba758178b6773298bc Mon Sep 17 00:00:00 2001
From: Rahul Joshi <rjoshi at nvidia.com>
Date: Wed, 15 Oct 2025 15:30:14 -0700
Subject: [PATCH 2/3] Add example of opaque class

---
 llvm/docs/CodingStandards.rst | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/llvm/docs/CodingStandards.rst b/llvm/docs/CodingStandards.rst
index 128892edf0772..fdb1932e09a48 100644
--- a/llvm/docs/CodingStandards.rst
+++ b/llvm/docs/CodingStandards.rst
@@ -860,13 +860,13 @@ your private interface remains private and undisturbed by outsiders.
     It's okay to put extra implementation methods in a public class itself. Just
     make them private (or protected) and all is well.
 
-Use Namespace Qualifiers to Define Previously Declared Variables and Functions
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Use Namespace Qualifiers to Define Previously Declared Entities
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-When providing an out-of-line definition of a variable or a function in a source
-file, do not open namespace blocks in the source file. Instead, use namespace
-qualifiers to help ensure that your definition matches an existing declaration.
-Do this:
+When providing an out-of-line definition for various entities (variables,
+functions, opaque classes) in a source file, do not open namespace blocks in the
+source file. Instead, use namespace qualifiers to help ensure that your
+definition matches an existing declaration. Do this:
 
 .. code-block:: c++
 
@@ -874,7 +874,11 @@ Do this:
   namespace llvm {
   extern int FooVal;
   int foo(const char *s);
-  }
+
+  namespace detail {
+  class FooImpl;
+  } // namespace detail
+  } // namespace llvm
 
   // Foo.cpp
   #include "Foo.h"
@@ -886,6 +890,10 @@ Do this:
     // ...
   }
 
+  class detail::FooImpl {
+    // ...
+  }
+
 Doing this helps to avoid bugs where the definition does not match the
 declaration from the header. For example, the following C++ code defines a new
 overload of ``llvm::foo`` instead of providing a definition for the existing

>From 444896cbe5d8c79a41db81fd52bc51c4e2b8a521 Mon Sep 17 00:00:00 2001
From: Rahul Joshi <rjoshi at nvidia.com>
Date: Mon, 20 Oct 2025 09:26:49 -0700
Subject: [PATCH 3/3] Review feedback

---
 llvm/docs/CodingStandards.rst | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/llvm/docs/CodingStandards.rst b/llvm/docs/CodingStandards.rst
index fdb1932e09a48..8677d894a94a6 100644
--- a/llvm/docs/CodingStandards.rst
+++ b/llvm/docs/CodingStandards.rst
@@ -860,10 +860,10 @@ your private interface remains private and undisturbed by outsiders.
     It's okay to put extra implementation methods in a public class itself. Just
     make them private (or protected) and all is well.
 
-Use Namespace Qualifiers to Define Previously Declared Entities
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Use Namespace Qualifiers to Define Previously Declared Symbols
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-When providing an out-of-line definition for various entities (variables,
+When providing an out-of-line definition for various symbols (variables,
 functions, opaque classes) in a source file, do not open namespace blocks in the
 source file. Instead, use namespace qualifiers to help ensure that your
 definition matches an existing declaration. Do this: