[PATCH] D117603: [clang] Don't typo-fix an expression in a SFINAE context

[Arthur O'Dwyer via Phabricator via cfe-commits]

Quuxplusone created this revision.
Quuxplusone added reviewers: ldionne, rsmith, leonardchan, mizvekov.
Quuxplusone added a project: clang.
Quuxplusone requested review of this revision.
Herald added a subscriber: cfe-commits.

If this is a SFINAE context, then continuing to look up names (in particular, to treat a non-function as a function, and then do ADL) might too-eagerly complete a type that it's not safe to complete right now. We should just say "okay, that's a substitution failure" and not do any more work than absolutely required.

Fixes https://github.com/llvm/llvm-project/issues/52970

      


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D117603

Files:
  clang/lib/Sema/Sema.cpp
  clang/lib/Sema/SemaExprMember.cpp
  clang/test/SemaCXX/PR52970.cpp


Index: clang/test/SemaCXX/PR52970.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/PR52970.cpp
@@ -0,0 +1,59 @@
+// RUN: %clang_cc1 -fsyntax-only -std=c++11 -verify %s
+// RUN: %clang_cc1 -fsyntax-only -std=c++14 -verify %s
+// RUN: %clang_cc1 -fsyntax-only -std=c++17 -verify %s
+// RUN: %clang_cc1 -fsyntax-only -std=c++20 -verify %s
+// expected-no-diagnostics
+
+struct Incomplete;
+template<class T> struct Holder { T t; };
+
+namespace DotFollowingFunctionName {
+  struct Good {
+    struct Nested {
+      int b;
+    } a;
+  };
+
+  struct Bad {
+    Holder<Incomplete> a();
+  };
+
+  template<class T>
+  constexpr auto f(T t) -> decltype((t.a.b, true))
+    { return true; }
+  constexpr bool f(...) { return false; }
+
+  static_assert(DotFollowingFunctionName::f(Good{}), "");
+  static_assert(!DotFollowingFunctionName::f(Bad{}), "");
+
+#if __cplusplus >= 202002L
+  template<class T>
+  concept C = requires (T t) { t.a.b; };
+
+  static_assert(C<Good>);
+  static_assert(!C<Bad>);
+#endif
+}
+
+namespace DotFollowingPointer {
+  struct Good {
+    int begin();
+  };
+  using Bad = Holder<Incomplete>*;
+
+  template<class T>
+  constexpr auto f(T t) -> decltype((t.begin(), true))
+    { return true; }
+  constexpr bool f(...) { return false; }
+
+  static_assert(DotFollowingPointer::f(Good{}), "");
+  static_assert(!DotFollowingPointer::f(Bad{}), "");
+
+#if __cplusplus >= 202002L
+  template<class T>
+  concept C = requires (T t) { t.begin(); };
+
+  static_assert(C<Good>);
+  static_assert(!C<Bad>);
+#endif
+}
Index: clang/lib/Sema/SemaExprMember.cpp
===================================================================
--- clang/lib/Sema/SemaExprMember.cpp
+++ clang/lib/Sema/SemaExprMember.cpp
@@ -1645,6 +1645,9 @@
           << BaseType << int(IsArrow) << BaseExpr.get()->getSourceRange()
           << FixItHint::CreateReplacement(OpLoc, "->");
 
+      if (S.isSFINAEContext())
+        return ExprError();
+
       // Recurse as an -> access.
       IsArrow = true;
       return LookupMemberExpr(S, R, BaseExpr, IsArrow, OpLoc, SS,
Index: clang/lib/Sema/Sema.cpp
===================================================================
--- clang/lib/Sema/Sema.cpp
+++ clang/lib/Sema/Sema.cpp
@@ -2552,6 +2552,10 @@
 bool Sema::tryToRecoverWithCall(ExprResult &E, const PartialDiagnostic &PD,
                                 bool ForceComplain,
                                 bool (*IsPlausibleResult)(QualType)) {
+  if (isSFINAEContext()) {
+    // If this is a SFINAE context, don't try anything that might trigger ADL prematurely.
+    return false;
+  }
   SourceLocation Loc = E.get()->getExprLoc();
   SourceRange Range = E.get()->getSourceRange();
 


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