Perform access checking to private members in simple requirement.

> Dependent access checks.

Fixes: https://github.com/llvm/llvm-project/issues/53364

We previously ignored dependent access checks to private members.
These are visible only to the `RequiresExprBodyExpr` (through `PerformDependentDiagnositcs`) and not to the individual requirements.

---

> Non-dependent access checks.
Fixes: https://github.com/llvm/llvm-project/issues/53334
Access to members in a non-dependent context would always yield an
invalid expression. When it appears in a requires-expression, then this
is a hard error as this would always result in a substitution failure.

https://eel.is/c++draft/expr.prim.req#general-note-1
> Note 1: If a requires-expression contains invalid types or expressions in its requirements, and it does not appear within the declaration of a templated entity, then the program is ill-formed. — end note]
> If the substitution of template arguments into a requirement would always result in a substitution failure, the program is ill-formed; no diagnostic required.

The main issue here is the delaying of the diagnostics.
Use a `ParsingDeclRAIIObject` creates a separate diagnostic pool for diagnositcs associated to the `RequiresExprBodyDecl`.
This is important because dependent diagnostics should not be leaked/delayed to higher scopes (Eg. inside a template function or in a trailing requires). These dependent diagnostics must be attached to the `DeclContext` of the parameters of `RequiresExpr` (which is the `RequiresExprBodyDecl` in this case).
Non dependent diagnostics, on the other hand, should not delayed and surfaced as hard errors.

Differential Revision: https://reviews.llvm.org/D140547

4 files changed, 25 insertions, 1 deletions

diff --git a/clang/lib/Parse/ParseExprCXX.cpp b/clang/lib/Parse/ParseExprCXX.cpp
index 5017f31..7f09120 100644
--- a/clang/lib/Parse/ParseExprCXX.cpp
+++ b/clang/lib/Parse/ParseExprCXX.cpp
@@ -3509,6 +3509,10 @@ ExprResult Parser::ParseRequiresExpression() {
       Actions, Sema::ExpressionEvaluationContext::Unevaluated);
 
   ParseScope BodyScope(this, Scope::DeclScope);
+  // Create a separate diagnostic pool for RequiresExprBodyDecl.
+  // Dependent diagnostics are attached to this Decl and non-depenedent
+  // diagnostics are surfaced after this parse.
+  ParsingDeclRAIIObject ParsingBodyDecl(*this, ParsingDeclRAIIObject::NoParent);
   RequiresExprBodyDecl *Body = Actions.ActOnStartRequiresExpr(
       RequiresKWLoc, LocalParameterDecls, getCurScope());
 
@@ -3746,6 +3750,7 @@ ExprResult Parser::ParseRequiresExpression() {
   }
   Braces.consumeClose();
   Actions.ActOnFinishRequiresExpr();
+  ParsingBodyDecl.complete(Body);
   return Actions.ActOnRequiresExpr(RequiresKWLoc, Body, LocalParameterDecls,
                                    Requirements, Braces.getCloseLocation());
 }
diff --git a/clang/lib/Sema/SemaAccess.cpp b/clang/lib/Sema/SemaAccess.cpp
index 00d3efd..cbda624 100644
--- a/clang/lib/Sema/SemaAccess.cpp
+++ b/clang/lib/Sema/SemaAccess.cpp
@@ -1493,6 +1493,8 @@ void Sema::HandleDelayedAccessCheck(DelayedDiagnostic &DD, Decl *D) {
   } else if (TemplateDecl *TD = dyn_cast<TemplateDecl>(D)) {
     if (isa<DeclContext>(TD->getTemplatedDecl()))
       DC = cast<DeclContext>(TD->getTemplatedDecl());
+  } else if (auto *RD = dyn_cast<RequiresExprBodyDecl>(D)) {
+    DC = RD;
   }
 
   EffectiveContext EC(DC);
diff --git a/clang/lib/Sema/SemaConcept.cpp b/clang/lib/Sema/SemaConcept.cpp
index cab013d..af92069 100644
--- a/clang/lib/Sema/SemaConcept.cpp
+++ b/clang/lib/Sema/SemaConcept.cpp
@@ -1002,6 +1002,7 @@ static void diagnoseWellFormedUnsatisfiedConstraintExpr(Sema &S,
     S.DiagnoseUnsatisfiedConstraint(CSE->getSatisfaction());
     return;
   } else if (auto *RE = dyn_cast<RequiresExpr>(SubstExpr)) {
+    // FIXME: RequiresExpr should store dependent diagnostics.
     for (concepts::Requirement *Req : RE->getRequirements())
       if (!Req->isDependent() && !Req->isSatisfied()) {
         if (auto *E = dyn_cast<concepts::ExprRequirement>(Req))
diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index 9757183..b43a754 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -15,6 +15,7 @@
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/ASTLambda.h"
 #include "clang/AST/ASTMutationListener.h"
+#include "clang/AST/DeclBase.h"
 #include "clang/AST/DeclTemplate.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/ExprConcepts.h"
@@ -1362,7 +1363,22 @@ namespace {
 
     ExprResult TransformRequiresExpr(RequiresExpr *E) {
       LocalInstantiationScope Scope(SemaRef, /*CombineWithOuterScope=*/true);
-      return inherited::TransformRequiresExpr(E);
+      auto TransReq = inherited::TransformRequiresExpr(E);
+      if (TransReq.isInvalid())
+        return TransReq;
+      assert(TransReq.get() != E &&
+             "Do not change value of isSatisfied for the existing expression. "
+             "Create a new expression instead.");
+      if (E->getBody()->isDependentContext()) {
+        Sema::SFINAETrap Trap(SemaRef);
+        // We recreate the RequiresExpr body, but not by instantiating it.
+        // Produce pending diagnostics for dependent access check.
+        SemaRef.PerformDependentDiagnostics(E->getBody(), TemplateArgs);
+        // FIXME: Store SFINAE diagnostics in RequiresExpr for diagnosis.
+        if (Trap.hasErrorOccurred())
+          TransReq.getAs<RequiresExpr>()->setSatisfied(false);
+      }
+      return TransReq;
     }
 
     bool TransformRequiresExprRequirements(