[Clang][NFC] Consolidate the parameter check for the requires expression parameter. (#110773)

This patch is a follow-up to #109831. In the discussion, we agreed that
having parameter checks scattered across different areas isn't ideal.
Therefore, I suggest merging the check from #88974 into the void
parameter check. This change won't impact functionality and will enhance
maintainability.

Author: c8ef

clang/lib/Parse/ParseDecl.cpp

@@ -7950,21 +7950,8 @@ 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_expr_explicit_object_parameter);
-    }
 
     ParsedTemplateInfo TemplateInfo;
     ParseDeclarationSpecifiers(DS, TemplateInfo, AS_none,

clang/lib/Sema/SemaExprCXX.cpp

@@ -9519,15 +9519,28 @@ Sema::ActOnStartRequiresExpr(SourceLocation RequiresKWLoc,
       } else if (Param->getType().hasQualifiers()) {
         Diag(Param->getBeginLoc(), diag::err_void_param_qualified);
       }
-    }
-
-    if (Param->hasDefaultArg())
+    } else if (Param->hasDefaultArg()) {
       // C++2a [expr.prim.req] p4
       //     [...] A local parameter of a requires-expression shall not have a
       //     default argument. [...]
       Diag(Param->getDefaultArgRange().getBegin(),
            diag::err_requires_expr_local_parameter_default_argument);
-    // Ignore default argument and move on
+      // Ignore default argument and move on
+    } else if (Param->isExplicitObjectParameter()) {
+      // 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.
+      Diag(Param->getExplicitObjectParamThisLoc(),
+           diag::err_requires_expr_explicit_object_parameter);
+      Param->setExplicitObjectParameterLoc(SourceLocation());
+    }
 
     Param->setDeclContext(Body);
     // If this has an identifier, add it to the scope stack.