[Clang] disallow attributes on void parameters

[a-tarasyuk]

Fixes #108819

---

This PR introduces diagnostics to disallow the use of attributes on void parameters

void f([[deprecated]] void) {}

[llvmbot]

@llvm/pr-subscribers-clang

Author: Oleksandr T. (a-tarasyuk)

Changes

Fixes #108819

---

This PR introduces diagnostics to disallow the use of attributes on void parameters

void f([[deprecated]] void) {}

---

Full diff: https://github.com/llvm/llvm-project/pull/124920.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+2)
• (modified) clang/lib/Parse/ParseDecl.cpp (+7)
• (modified) clang/test/Parser/cxx0x-attributes.cpp (+9)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 7fafe2807bd388..0c87e52007d546 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -100,6 +100,8 @@ Removed Compiler Flags
 Attribute Changes in Clang
 --------------------------
 
+- Clang now disallows the use of attributes on void parameters. (#GH108819)
+
 Improvements to Clang's diagnostics
 -----------------------------------
 
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index f136d5007e8a5f..0b88dd4449b1e2 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -7986,6 +7986,13 @@ void Parser::ParseParameterDeclarationClause(
     if (getLangOpts().HLSL)
       MaybeParseHLSLAnnotations(DS.getAttributes());
 
+    if (ParmDeclarator.getIdentifier() == nullptr &&
+        ParmDeclarator.getDeclarationAttributes().size() &&
+        ParmDeclarator.getDeclSpec().getTypeSpecType() == DeclSpec::TST_void) {
+      SourceRange AttrRange = ParmDeclarator.getDeclarationAttributes().Range;
+      Diag(AttrRange.getBegin(), diag::err_attributes_not_allowed) << AttrRange;
+    }
+
     if (Tok.is(tok::kw_requires)) {
       // User tried to define a requires clause in a parameter declaration,
       // which is surely not a function declaration.
diff --git a/clang/test/Parser/cxx0x-attributes.cpp b/clang/test/Parser/cxx0x-attributes.cpp
index fad3010c98b9c2..13fcdd142fa841 100644
--- a/clang/test/Parser/cxx0x-attributes.cpp
+++ b/clang/test/Parser/cxx0x-attributes.cpp
@@ -453,3 +453,12 @@ namespace P2361 {
 }
 
 alignas(int) struct AlignAsAttribute {}; // expected-error {{misplaced attributes; expected attributes here}}
+
+namespace GH108819 {
+void a([[maybe_unused]] void) {}                 // expected-error {{an attribute list cannot appear here}} \
+                                                 // expected-warning {{use of the 'maybe_unused' attribute is a C++17 extension}}
+void b([[deprecated]] void) {}                   // expected-error {{an attribute list cannot appear here}} \
+                                                 // expected-warning {{use of the 'deprecated' attribute is a C++14 extension}}
+void c([[clang::lifetimebound]] void) {}         // expected-error {{an attribute list cannot appear here}}
+void d([[clang::annotate("a", "b", 1)]] void) {} // expected-error {{an attribute list cannot appear here}}
+}

[erichkeane]

1 nit, else LGTM.

[AaronBallman]

This is a semantic restriction, not a parsing restriction, right?

[github-actions]

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

[AaronBallman]

LGTM, thank you for the fix!

[shafik]

This makes sense but we should have been coverage in testing.

[shafik]

Can we add a test for a member function. also a templated function, lambdas as well. Other combination if you can come up w/ them should also be tested. We need to do a better job of covering as much as possible.

[a-tarasyuk]

@shafik Thanks for the feedback. I've added more test cases. Could you take a look?

[AaronBallman]

LGTM!