[Clang][Parse] Diagnose requires expressions with explicit object parameters

[sdkrystian]

Clang currently allows the following:

auto x = requires (this int) { true; };

This patch addresses that.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Krystian Stasiowski (sdkrystian)

Changes

Clang currently allows the following:

auto x = requires (this int) { true; };

This patch addresses that.

---

Full diff: https://github.com/llvm/llvm-project/pull/88974.diff

4 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+2)
• (modified) clang/include/clang/Basic/DiagnosticParseKinds.td (+2)
• (modified) clang/lib/Parse/ParseDecl.cpp (+14-1)
• (added) clang/test/CXX/dcl.decl/dcl.meaning/dcl.fct/p6-cxx23.cpp (+4)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 76701dc723b6c3..8a90c45a9b3638 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -366,6 +366,8 @@ Improvements to Clang's diagnostics
 - Clang now uses the correct type-parameter-key (``class`` or ``typename``) when printing
   template template parameter declarations.
 
+- Clang now diagnoses requires expressions with explicit object parameters.
+
 Improvements to Clang's time-trace
 ----------------------------------
 
diff --git a/clang/include/clang/Basic/DiagnosticParseKinds.td b/clang/include/clang/Basic/DiagnosticParseKinds.td
index bb9ca2a50cc06c..217ea9380f3b99 100644
--- a/clang/include/clang/Basic/DiagnosticParseKinds.td
+++ b/clang/include/clang/Basic/DiagnosticParseKinds.td
@@ -373,6 +373,8 @@ def err_requires_clause_must_appear_after_trailing_return : Error<
   "trailing return type must appear before trailing requires clause">;
 def err_requires_clause_on_declarator_not_declaring_a_function : Error<
   "trailing requires clause can only be used when declaring a function">;
+def err_requires_clause_explicit_object_parameter: Error<
+  "a requires clause cannot have an explicit object parameter">;
 def err_requires_clause_inside_parens : Error<
   "trailing requires clause should be placed outside parentheses">;
 def ext_auto_storage_class : ExtWarn<
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 2b934234b7cf5d..f9e2ab073e9719 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -7659,8 +7659,21 @@ void Parser::ParseParameterDeclarationClause(
     // Parse a C++23 Explicit Object Parameter
     // We do that in all language modes to produce a better diagnostic.
     SourceLocation ThisLoc;
-    if (getLangOpts().CPlusPlus && Tok.is(tok::kw_this))
+    if (getLangOpts().CPlusPlus && Tok.is(tok::kw_this)) {
       ThisLoc = ConsumeToken();
+      // C++23 [dcl.fct]p6:
+      //   An explicit-object-parameter-declaration is a parameter-declaration
+      //   with a this specifier. An explicit-object-parameter-declaration
+      //   shall appear only as the first parameter-declaration of a
+      //   parameter-declaration-list of either:
+      //   - a member-declarator that declares a member function, or
+      //   - a lambda-declarator.
+      //
+      // The parameter-declaration-list of a requires-expression is not such
+      // a context.
+      if (DeclaratorCtx == DeclaratorContext::RequiresExpr)
+        Diag(ThisLoc, diag::err_requires_clause_explicit_object_parameter);
+    }
 
     ParseDeclarationSpecifiers(DS, /*TemplateInfo=*/ParsedTemplateInfo(),
                                AS_none, DeclSpecContext::DSC_normal,
diff --git a/clang/test/CXX/dcl.decl/dcl.meaning/dcl.fct/p6-cxx23.cpp b/clang/test/CXX/dcl.decl/dcl.meaning/dcl.fct/p6-cxx23.cpp
new file mode 100644
index 00000000000000..d31e68acb64ac5
--- /dev/null
+++ b/clang/test/CXX/dcl.decl/dcl.meaning/dcl.fct/p6-cxx23.cpp
@@ -0,0 +1,4 @@
+// RUN: %clang_cc1 -std=c++23 -fsyntax-only -verify %s
+
+auto x0 = requires (this int) { true; }; // expected-error {{a requires clause cannot have an explicit object parameter}}
+auto x1 = requires (int, this int) { true; }; // expected-error {{a requires clause cannot have an explicit object parameter}}

[cor3ntin]

Thanks for spotting that. I think there are further cases that I'm not sure we protect against

[cor3ntin]

Can you add a test for template <this auto> void f() ?

[sdkrystian]

@cor3ntin sure, but non-type template parameter parsing doesn't use ParseParameterDeclarationClause -- it is done in ParseNonTypeTemplateParameter

[cor3ntin]

LGTM