[clang] 5402948 - [Clang] Reject increment of bool value in unevaluated contexts after C++17

[via cfe-commits]

Author: yronglin
Date: 2023-06-06T23:58:37+08:00
New Revision: 540294845babbb2be909ea456323d7bc8a1763df

URL: https://github.com/llvm/llvm-project/commit/540294845babbb2be909ea456323d7bc8a1763df
DIFF: https://github.com/llvm/llvm-project/commit/540294845babbb2be909ea456323d7bc8a1763df.diff

LOG: [Clang] Reject increment of bool value in unevaluated contexts after C++17

Clang now incorrectly allowed increment of bool in unevaluated contexts, we set `diagnostic::ext_increment_bool` to be SFINAEFailure to fix this issue.

```
template<class T> auto f(T t) -> decltype(++t);
auto f(...) -> void;
void g() {
  f(true);  // Clang wrongly makes this a hard error
}
```

```
template <class T>
concept can_increment = requires(T t) { ++t; };

template <class T> void f() {
  static_assert(requires(T t) { ++t; }); // Incorrectly allowed
}

int main() {
  f<bool>();

  static_assert(!can_increment<bool>); // Incorrectly fails

  bool b = false;
  ++b; // Correctly rejected
}
```
Fix issue: https://github.com/llvm/llvm-project/issues/47517

Reviewed By: erichkeane

Differential Revision: https://reviews.llvm.org/D152259

Added: 
    clang/test/SemaCXX/bool-increment-SFINAE.cpp

Modified: 
    clang/docs/ReleaseNotes.rst
    clang/include/clang/Basic/DiagnosticSemaKinds.td

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 9bbf270c27476..6f582f584bdf6 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -476,6 +476,8 @@ Bug Fixes in This Version
 - Fix crash when passing a braced initializer list to a parentehsized aggregate
   initialization expression.
   (`#63008 <https://github.com/llvm/llvm-project/issues/63008>`_).
+- Reject increment of bool value in unevaluated contexts after C++17.
+  (`#47517 <https://github.com/llvm/llvm-project/issues/47517>`_).
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

diff  --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 90ecbd623ceef..5895888c175fa 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -7661,7 +7661,7 @@ def warn_increment_bool : Warning<
   "incompatible with C++17">, InGroup<DeprecatedIncrementBool>;
 def ext_increment_bool : ExtWarn<
   "ISO C++17 does not allow incrementing expression of type bool">,
-  DefaultError, InGroup<IncrementBool>;
+  DefaultError, SFINAEFailure, InGroup<IncrementBool>;
 def err_increment_decrement_enum : Error<
   "cannot %select{decrement|increment}0 expression of enum type %1">;
 

diff  --git a/clang/test/SemaCXX/bool-increment-SFINAE.cpp b/clang/test/SemaCXX/bool-increment-SFINAE.cpp
new file mode 100644
index 0000000000000..d3889293fc0b6
--- /dev/null
+++ b/clang/test/SemaCXX/bool-increment-SFINAE.cpp
@@ -0,0 +1,37 @@
+// RUN: %clang_cc1 %std_cxx98-14 -fsyntax-only -verify=precxx17 %s
+// RUN: %clang_cc1 -std=c++17 -fsyntax-only -verify=expected %s
+// RUN: %clang_cc1 -std=c++17 -DFAILED_CXX17 -fsyntax-only -verify=failcxx17 %s
+// RUN: %clang_cc1 %std_cxx20- -fsyntax-only -verify=cxx20 %s
+// expected-no-diagnostics
+
+template<class T> auto f(T t) -> decltype(++t); // precxx17-warning {{incrementing expression of type bool is deprecated}}
+
+auto f(...) -> void;
+void g() { f(true); }
+
+#ifdef FAILED_CXX17
+
+template<class T> auto f1(T t) -> decltype(++t); // failcxx17-note {{candidate template ignored: substitution failure [with T = bool]: ISO C++17 does not allow incrementing expression of type bool}}
+auto f1(void) -> void; // failcxx17-note {{candidate function not viable: requires 0 arguments, but 1 was provided}}
+void g1() { f1(true); } // failcxx17-error {{no matching function for call to 'f1'}}
+
+#endif
+
+#if __cplusplus >= 202002L
+template <class T>
+concept can_increment = requires(T t) {
+  ++t;
+};
+
+template <class T>
+void f() {
+  static_assert(requires(T t) { ++t; }); // cxx20-error {{static assertion failed due to requirement 'requires (bool t) { <<error-expression>>; }'}}
+}
+
+int main() {
+  f<bool>(); // cxx20-note {{in instantiation of function template specialization 'f<bool>' requested here}}
+  static_assert(!can_increment<bool>); 
+
+  return 0;
+}
+#endif