[clang] Replace Member Expressions During Instantiation If Necessary

[lime]

Summary

This patch replaces member accesses to declaration references during template
instantiation if the context is the unevaluated context and the class does not
contain the declaration.

The replacement fixes the issue #58674. Unlike previous fixes such as D143840,
it checks the membership during instantiation rather than right after parsing,
so the check is more accurate and efficient.

This patch also includes cases that previous fixes had once failed on.

[erichkeane]

Other than the two auto's missing a *, I think this is alright. I want to think about it/give others a chance to review, so please ping this in a few days if it hasn't been accepted by then.

clang/lib/Sema/TreeTransform.h

2808

2812

[lime]

Update and ping.

[erichkeane]

Thanks for the ping. I don't have any better ideas/other thoughts, so LGTM.

clang/docs/ReleaseNotes.rst

 ^^^^^^^^^^^^^^^^^^^^^^^^
 
 - Fix crash on invalid code when looking up a destructor in a templated class
   inside a namespace.
   (`#59446 <https://github.com/llvm/llvm-project/issues/59446>`_)
 - Fix crash when evaluating consteval constructor of derived class whose base
   has more than one field.
   (`#60166 <https://github.com/llvm/llvm-project/issues/60166>`_)
+- Fix an issue about ``decltype`` in the members of class templates derived from
+  templates with related parameters.
+  (`#58674 <https://github.com/llvm/llvm-project/issues/58674>`_)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Miscellaneous Bug Fixes
 ^^^^^^^^^^^^^^^^^^^^^^^
 
 Miscellaneous Clang Crashes Fixed

clang/lib/Sema/TreeTransform.h

if (isArrow && !BaseType->isPointerType())
       return ExprError();
 
     // FIXME: this involves duplicating earlier analysis in a lot of
     // cases; we should avoid this when possible.
     LookupResult R(getSema(), MemberNameInfo, Sema::LookupMemberName);
     R.addDecl(FoundDecl);
     R.resolveKind();
 
+    if (getSema().isUnevaluatedContext() && Base->isImplicitCXXThis() &&
+        isa<FieldDecl, IndirectFieldDecl, MSPropertyDecl>(Member)) {
+      if (auto *ThisClass = cast<CXXThisExpr>(Base)
+                                ->getType()
+                                ->getPointeeType()
+                                ->getAsCXXRecordDecl()) {
+        auto *Class = cast<CXXRecordDecl>(Member->getDeclContext());
+        // In unevaluated contexts, an expression supposed to be a member access
+        // might reference a member in an unrelated class.
+        if (!ThisClass->Equals(Class) && !ThisClass->isDerivedFrom(Class))
+          return getSema().BuildDeclRefExpr(Member, Member->getType(),
+                                            VK_LValue, Member->getLocation());
+      }
+    }
+
     return getSema().BuildMemberReferenceExpr(Base, BaseType, OpLoc, isArrow,
                                               SS, TemplateKWLoc,
                                               FirstQualifierInScope,
                                               R, ExplicitTemplateArgs,
                                               /*S*/nullptr);
   }
 
   /// Build a new binary operator expression.

clang/test/CodeGenCXX/decl-ref-inheritance.cpp

+// RUN: %clang_cc1 -triple=x86_64-unknown-linux -emit-llvm %s -o - | FileCheck \
+// RUN: -check-prefix=CHECK-1 %s
+// RUN: %clang_cc1 -triple=x86_64-unknown-linux -emit-llvm %s -o - | FileCheck \
+// RUN: -check-prefix=CHECK-2 %s
+// RUN: %clang_cc1 -triple=x86_64-unknown-linux -emit-llvm %s -o - | FileCheck \
+// RUN: -check-prefix=CHECK-3 %s
+
+// CHECK-1: [[FOO:%.+]] = type { float }
+struct foo {
+  float val;
+};
+
+template <typename T> struct bar : T {
+};
+
+struct baz : bar<foo> {
+  // CHECK-1: define{{.*}} float @_ZN3baz3getEv
+  // CHECK-1: {{%.+}} = getelementptr inbounds [[FOO]], ptr {{%.+}}, i32 0, i32 0
+  float get() {
+    return val;
+  }
+};
+
+int qux() {
+  auto f = baz{};
+  return f.get();
+}
+
+// CHECK-2: [[F:%.+]] = type { ptr }
+struct f {
+  void *g;
+};
+
+template <typename j> struct k : j {
+  // CHECK-2: define{{.*}} void @_ZN1kI1fE1lEv
+  // CHECK-2: {{%.+}} = getelementptr inbounds [[F]], ptr {{%.+}}, i32 0, i32 0
+  virtual void l(){ (void)f::g; }
+};
+
+k<f> q;
+
+// CHECK-3: [[BASE:%.+]] = type { i32 }
+class Base {
+protected:
+  int member;
+};
+
+template <typename Parent>
+struct Subclass : public Parent {
+  // CHECK-3: define{{.*}} i32 @_ZN8SubclassI4BaseE4funcEv
+  // CHECK-3: {{%.+}} = getelementptr inbounds [[BASE]], ptr {{%.+}}, i32 0, i32 0
+  int func() { return Base::member; }
+};
+
+using Impl = Subclass<Base>;
+
+int use() {
+  Impl i;
+  return i.func();
+}

clang/test/SemaCXX/decltype.cpp

namespace D5789 {
   void foo(decltype(T(LP1{ .p1 = { "foo" }, .p1.x[1] = 'x'}))) {} // okay
 
   // expected-warning@+3 {{initializer partially overrides}}
   // expected-note@+2 {{previous initialization}}
   // expected-error@+1 {{redefinition of 'foo'}}
   template<class T> void foo(decltype(T(LP1{ .p1 = g1, .p1.x[1] = 'x' }))) {}
 }
 
+namespace GH58674 {
+  struct Foo {
+    float value_;
+    struct nested {
+      float value_;
+    };
+  };
+
+  template <typename T>
+  struct TemplateFoo {
+    float value_;
+  };
+
+  float bar;
+
+  template <typename T>
+  struct Animal{};
+
+  template <typename T>
+  class Cat : Animal<T> {
+    using okay = decltype(Foo::value_);
+    using also_okay = decltype(bar);
+    using okay2 = decltype(Foo::nested::value_);
+    using okay3 = decltype(TemplateFoo<T>::value_);
+  public:
+    void meow() {
+      using okay = decltype(Foo::value_);
+      using also_okay = decltype(bar);
+      using okay2 = decltype(Foo::nested::value_);
+      using okay3 = decltype(TemplateFoo<T>::value_);
+    }
+  };
+
+  void baz() {
+      Cat<void>{}.meow();
+  }
+}
+
 template<typename>
 class conditional {
 };
 
 // FIXME: The diagnostics here are produced twice.
 void foo(conditional<decltype((1),int>) {  // expected-note 2 {{to match this '('}} expected-error {{expected ')'}} expected-note 2{{to match this '<'}}
 } // expected-error {{expected function body after function declarator}} expected-error 2 {{expected '>'}} expected-error {{expected ')'}}