[clang] [Clang] Warn on deprecated specializations used in system headers. (PR #70353)
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Fri Nov 17 07:41:10 PST 2023
https://github.com/cor3ntin updated https://github.com/llvm/llvm-project/pull/70353
>From be2381c9e795af6dc6eec9a3eb9a0ef467edfe5c Mon Sep 17 00:00:00 2001
From: Corentin Jabot <corentinjabot at gmail.com>
Date: Thu, 26 Oct 2023 18:40:15 +0200
Subject: [PATCH 1/2] [Clang] Warn on deprecated specializations used in system
headers.
When the top of the instantiation stack is in user code.
Thge goal of this PR is to allow deprecation of some char_traits
specializations in libc++ as done in https://reviews.llvm.org/D157058
which was later reverted by
https://github.com/llvm/llvm-project/pull/66153#issuecomment-1719578384
As Clang never emitted the libc++ warnings.
Because Clang likes to eagerly instantiate, we
look for the location of the top of the instantiation stack,
and emit a warning if that location is in user code.
The warning emission is forced by temporarily instruct the diag
engine not to silence warning in system headers,
---
clang/docs/ReleaseNotes.rst | 2 ++
clang/include/clang/Sema/Sema.h | 2 ++
clang/lib/Sema/SemaAvailability.cpp | 23 +++++++++++++++
clang/lib/Sema/SemaTemplate.cpp | 22 +++++++++++++++
...ated-specializations-in-system-headers.cpp | 28 +++++++++++++++++++
5 files changed, 77 insertions(+)
create mode 100644 clang/test/SemaCXX/warn-deprecated-specializations-in-system-headers.cpp
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 08ffb08e341ab43..79534687139cc3a 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -444,6 +444,8 @@ Improvements to Clang's diagnostics
- ``-Wzero-as-null-pointer-constant`` diagnostic is no longer emitted when using ``__null``
(or, more commonly, ``NULL`` when the platform defines it as ``__null``) to be more consistent
with GCC.
+- Clang will warn on deprecated specializations used in system headers when their instantiation
+ is caused by user code.
Improvements to Clang's time-trace
----------------------------------
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 501dc01200a1c34..73981a4d657d49b 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -8464,6 +8464,8 @@ class Sema final {
ArrayRef<TemplateArgument> SugaredConverted,
ArrayRef<TemplateArgument> CanonicalConverted, bool &HasDefaultArg);
+ SourceLocation getTopMostPointOfInstantiation(const NamedDecl *) const;
+
/// Specifies the context in which a particular template
/// argument is being checked.
enum CheckTemplateArgumentKind {
diff --git a/clang/lib/Sema/SemaAvailability.cpp b/clang/lib/Sema/SemaAvailability.cpp
index 84c06566387ccbe..846a31a79673096 100644
--- a/clang/lib/Sema/SemaAvailability.cpp
+++ b/clang/lib/Sema/SemaAvailability.cpp
@@ -536,6 +536,29 @@ static void DoEmitAvailabilityWarning(Sema &S, AvailabilityResult K,
}
}
+ // We emit deprecation warning for deprecated specializations
+ // when their instantiation stacks originate outside
+ // of a system header, even if the diagnostics is suppresed at the
+ // point of definition.
+ SourceLocation InstantiationLoc =
+ S.getTopMostPointOfInstantiation(ReferringDecl);
+ bool ShouldAllowWarningInSystemHeader =
+ InstantiationLoc != Loc &&
+ !S.getSourceManager().isInSystemHeader(InstantiationLoc);
+ struct AllowWarningInSystemHeaders {
+ AllowWarningInSystemHeaders(DiagnosticsEngine &E,
+ bool AllowWarningInSystemHeaders)
+ : Engine(E), Prev(E.getSuppressSystemWarnings()) {
+ E.setSuppressSystemWarnings(!AllowWarningInSystemHeaders);
+ }
+ ~AllowWarningInSystemHeaders() { Engine.setSuppressSystemWarnings(Prev); }
+
+ private:
+ DiagnosticsEngine &Engine;
+ bool Prev;
+ } SystemWarningOverrideRAII(S.getDiagnostics(),
+ ShouldAllowWarningInSystemHeader);
+
if (!Message.empty()) {
S.Diag(Loc, diag_message) << ReferringDecl << Message << FixIts;
if (ObjCProperty)
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 766ebd90fded0c4..cbf63172a1e3052 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -11601,3 +11601,25 @@ void Sema::checkSpecializationReachability(SourceLocation Loc,
Sema::AcceptableKind::Reachable)
.check(Spec);
}
+
+/// Returns the top most location responsible for the definition of \p N.
+/// If \p N is a a template specialization, this is the location
+/// of the top of the instantiation stack.
+/// Otherwise, the location of \p N is returned.
+SourceLocation Sema::getTopMostPointOfInstantiation(const NamedDecl *N) const {
+ if (!getLangOpts().CPlusPlus || CodeSynthesisContexts.empty())
+ return N->getLocation();
+ if (auto *FD = dyn_cast<FunctionDecl>(N)) {
+ if (!FD->isFunctionTemplateSpecialization())
+ return FD->getLocation();
+ } else if (!isa<ClassTemplateSpecializationDecl,
+ VarTemplateSpecializationDecl>(N)) {
+ return N->getLocation();
+ }
+ for (const CodeSynthesisContext &CSC : CodeSynthesisContexts) {
+ if (!CSC.isInstantiationRecord() || CSC.PointOfInstantiation.isInvalid())
+ continue;
+ return CSC.PointOfInstantiation;
+ }
+ return N->getLocation();
+}
diff --git a/clang/test/SemaCXX/warn-deprecated-specializations-in-system-headers.cpp b/clang/test/SemaCXX/warn-deprecated-specializations-in-system-headers.cpp
new file mode 100644
index 000000000000000..270e4292bf9a47b
--- /dev/null
+++ b/clang/test/SemaCXX/warn-deprecated-specializations-in-system-headers.cpp
@@ -0,0 +1,28 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+#ifdef BE_THE_HEADER
+#pragma clang system_header
+
+template <typename T>
+struct traits;
+
+template <>
+struct [[ deprecated]] traits<int> {}; // expected-note {{'traits<int>' has been explicitly marked deprecated here}}
+
+template<typename T, typename Trait = traits<T>> // expected-warning {{'traits<int>' is deprecated}}
+struct basic_string {};
+
+// should not warn, defined and used in system headers
+using __do_what_i_say_not_what_i_do = traits<int> ;
+
+template<typename T, typename Trait = traits<double>>
+struct should_not_warn {};
+
+#else
+#define BE_THE_HEADER
+#include __FILE__
+
+basic_string<int> test1; // expected-note {{in instantiation of default argument for 'basic_string<int>' required here}}
+should_not_warn<int> test2;
+
+#endif
>From 5a43d23957e0672f1207e7002f8eef71f67a9fec Mon Sep 17 00:00:00 2001
From: Corentin Jabot <corentinjabot at gmail.com>
Date: Fri, 17 Nov 2023 16:40:52 +0100
Subject: [PATCH 2/2] Address Aaron's feedback
---
clang/lib/Sema/SemaTemplate.cpp | 2 +-
.../warn-deprecated-specializations-in-system-headers.cpp | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index cbf63172a1e3052..c188dd34014a4b3 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -11609,7 +11609,7 @@ void Sema::checkSpecializationReachability(SourceLocation Loc,
SourceLocation Sema::getTopMostPointOfInstantiation(const NamedDecl *N) const {
if (!getLangOpts().CPlusPlus || CodeSynthesisContexts.empty())
return N->getLocation();
- if (auto *FD = dyn_cast<FunctionDecl>(N)) {
+ if (const auto *FD = dyn_cast<FunctionDecl>(N)) {
if (!FD->isFunctionTemplateSpecialization())
return FD->getLocation();
} else if (!isa<ClassTemplateSpecializationDecl,
diff --git a/clang/test/SemaCXX/warn-deprecated-specializations-in-system-headers.cpp b/clang/test/SemaCXX/warn-deprecated-specializations-in-system-headers.cpp
index 270e4292bf9a47b..79c9d339b6f2058 100644
--- a/clang/test/SemaCXX/warn-deprecated-specializations-in-system-headers.cpp
+++ b/clang/test/SemaCXX/warn-deprecated-specializations-in-system-headers.cpp
@@ -7,7 +7,7 @@ template <typename T>
struct traits;
template <>
-struct [[ deprecated]] traits<int> {}; // expected-note {{'traits<int>' has been explicitly marked deprecated here}}
+struct [[deprecated]] traits<int> {}; // expected-note {{'traits<int>' has been explicitly marked deprecated here}}
template<typename T, typename Trait = traits<T>> // expected-warning {{'traits<int>' is deprecated}}
struct basic_string {};
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