[cfe-commits] r124217 - in /cfe/trunk: docs/LanguageExtensions.html include/clang/Basic/Attr.td include/clang/Basic/DiagnosticSemaKinds.td include/clang/Sema/AttributeList.h lib/Sema/AttributeList.cpp lib/Sema/SemaDeclAttr.cpp lib/Sema/SemaExprCXX.cpp test/SemaCXX/forbid-temporaries.cpp
Jeffrey Yasskin
jyasskin at google.com
Tue Jan 25 12:08:13 PST 2011
Author: jyasskin
Date: Tue Jan 25 14:08:12 2011
New Revision: 124217
URL: http://llvm.org/viewvc/llvm-project?rev=124217&view=rev
Log:
Add an attribute to forbid temporary instances of a type. This allows class
authors to write
class __attribute__((forbid_temporaries)) Name { ... };
when they want to force users to name all variables of the type. This protects
people from doing things like creating a scoped_lock that only lives for a
single statement instead of an entire scope.
The warning produced by this attribute can be disabled by
-Wno-forbid-temporaries.
Added:
cfe/trunk/test/SemaCXX/forbid-temporaries.cpp
Modified:
cfe/trunk/docs/LanguageExtensions.html
cfe/trunk/include/clang/Basic/Attr.td
cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
cfe/trunk/include/clang/Sema/AttributeList.h
cfe/trunk/lib/Sema/AttributeList.cpp
cfe/trunk/lib/Sema/SemaDeclAttr.cpp
cfe/trunk/lib/Sema/SemaExprCXX.cpp
Modified: cfe/trunk/docs/LanguageExtensions.html
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/docs/LanguageExtensions.html?rev=124217&r1=124216&r2=124217&view=diff
==============================================================================
--- cfe/trunk/docs/LanguageExtensions.html (original)
+++ cfe/trunk/docs/LanguageExtensions.html Tue Jan 25 14:08:12 2011
@@ -25,6 +25,7 @@
<li><a href="#vectors">Vectors and Extended Vectors</a></li>
<li><a href="#deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> attributes</a></li>
<li><a href="#attributes-on-enumerators">Attributes on enumerators</a></li>
+<li><a href="#forbid-temporaries-attribute">Attribute to forbid temporaries of a type</a></li>
<li><a href="#checking_language_features">Checks for Standard Language Features</a></li>
<ul>
<li><a href="#cxx_exceptions">C++ exceptions</a></li>
@@ -341,6 +342,33 @@
<p>Query for this feature with <tt>__has_feature(enumerator_attributes)</tt>.</p>
<!-- ======================================================================= -->
+<h2 id="forbid-temporaries-attribute">Attribute to forbid temporaries of a type</h2>
+<!-- ======================================================================= -->
+
+<p>Clang provides a <tt>forbid_temporaries</tt> attribute to forbid
+temporaries of a particular type.</p>
+
+<blockquote>
+<pre>class __attribute__((forbid_temporaries)) scoped_lock {
+ ...
+};</pre>
+</blockquote>
+
+<p>This prevents mistakes like</p>
+
+<blockquote>
+<pre>void foo() {
+ scoped_lock(my_mutex);
+ // Forgot the local variable name, so destructor runs here.
+ code_that_needs_lock_held();
+ // User expects destructor to run here.
+};</pre>
+</blockquote>
+
+<p>Query for this feature with <tt>__has_attribute(forbid_temporaries)</tt>.
+Use <tt>-Wno-forbid-temporaries</tt> to disable the resulting warning.</p>
+
+<!-- ======================================================================= -->
<h2 id="checking_language_features">Checks for Standard Language Features</h2>
<!-- ======================================================================= -->
Modified: cfe/trunk/include/clang/Basic/Attr.td
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/Attr.td?rev=124217&r1=124216&r2=124217&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/Attr.td (original)
+++ cfe/trunk/include/clang/Basic/Attr.td Tue Jan 25 14:08:12 2011
@@ -232,6 +232,11 @@
let Spellings = [];
}
+def ForbidTemporaries : Attr {
+ let Spellings = ["forbid_temporaries"];
+ let Subjects = [CXXRecord];
+}
+
def Format : InheritableAttr {
let Spellings = ["format"];
let Args = [StringArgument<"Type">, IntArgument<"FormatIdx">,
Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=124217&r1=124216&r2=124217&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
+++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Tue Jan 25 14:08:12 2011
@@ -856,6 +856,9 @@
"of type %1 invokes deleted constructor">;
def err_temp_copy_incomplete : Error<
"copying a temporary object of incomplete type %0">;
+def warn_temporaries_forbidden : Warning<
+ "must not create temporaries of type %0">,
+ InGroup<DiagGroup<"forbid-temporaries">>;
// C++0x decltype
def err_cannot_determine_declared_type_of_overloaded_function : Error<
Modified: cfe/trunk/include/clang/Sema/AttributeList.h
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Sema/AttributeList.h?rev=124217&r1=124216&r2=124217&view=diff
==============================================================================
--- cfe/trunk/include/clang/Sema/AttributeList.h (original)
+++ cfe/trunk/include/clang/Sema/AttributeList.h Tue Jan 25 14:08:12 2011
@@ -104,6 +104,7 @@
AT_dllimport,
AT_ext_vector_type,
AT_fastcall,
+ AT_forbid_temporaries,
AT_format,
AT_format_arg,
AT_global,
Modified: cfe/trunk/lib/Sema/AttributeList.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/AttributeList.cpp?rev=124217&r1=124216&r2=124217&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/AttributeList.cpp (original)
+++ cfe/trunk/lib/Sema/AttributeList.cpp Tue Jan 25 14:08:12 2011
@@ -85,6 +85,7 @@
.Case("deprecated", AT_deprecated)
.Case("visibility", AT_visibility)
.Case("destructor", AT_destructor)
+ .Case("forbid_temporaries", AT_forbid_temporaries)
.Case("format_arg", AT_format_arg)
.Case("gnu_inline", AT_gnu_inline)
.Case("weak_import", AT_weak_import)
Modified: cfe/trunk/lib/Sema/SemaDeclAttr.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDeclAttr.cpp?rev=124217&r1=124216&r2=124217&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaDeclAttr.cpp (original)
+++ cfe/trunk/lib/Sema/SemaDeclAttr.cpp Tue Jan 25 14:08:12 2011
@@ -885,6 +885,24 @@
d->addAttr(::new (S.Context) VecReturnAttr(Attr.getLoc(), S.Context));
}
+static void HandleForbidTemporariesAttr(Decl *d, const AttributeList &Attr,
+ Sema &S) {
+ assert(Attr.isInvalid() == false);
+
+ if (Attr.getNumArgs() != 0) {
+ S.Diag(Attr.getLoc(), diag::err_attribute_wrong_number_arguments) << 0;
+ return;
+ }
+
+ if (!isa<TypeDecl>(d)) {
+ S.Diag(Attr.getLoc(), diag::warn_attribute_wrong_decl_type)
+ << Attr.getName() << 9 /*class*/;
+ return;
+ }
+
+ d->addAttr(::new (S.Context) ForbidTemporariesAttr(Attr.getLoc(), S.Context));
+}
+
static void HandleDependencyAttr(Decl *d, const AttributeList &Attr, Sema &S) {
if (!isFunctionOrMethod(d) && !isa<ParmVarDecl>(d)) {
S.Diag(Attr.getLoc(), diag::err_attribute_wrong_decl_type)
@@ -2674,6 +2692,8 @@
case AttributeList::AT_ext_vector_type:
HandleExtVectorTypeAttr(scope, D, Attr, S);
break;
+ case AttributeList::AT_forbid_temporaries:
+ HandleForbidTemporariesAttr(D, Attr, S); break;
case AttributeList::AT_format: HandleFormatAttr (D, Attr, S); break;
case AttributeList::AT_format_arg: HandleFormatArgAttr (D, Attr, S); break;
case AttributeList::AT_global: HandleGlobalAttr (D, Attr, S); break;
Modified: cfe/trunk/lib/Sema/SemaExprCXX.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaExprCXX.cpp?rev=124217&r1=124216&r2=124217&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaExprCXX.cpp (original)
+++ cfe/trunk/lib/Sema/SemaExprCXX.cpp Tue Jan 25 14:08:12 2011
@@ -3188,9 +3188,12 @@
}
}
+ CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
+ if (RD->getAttr<ForbidTemporariesAttr>())
+ Diag(E->getExprLoc(), diag::warn_temporaries_forbidden) << E->getType();
+
// That should be enough to guarantee that this type is complete.
// If it has a trivial destructor, we can avoid the extra copy.
- CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
if (RD->isInvalidDecl() || RD->hasTrivialDestructor())
return Owned(E);
Added: cfe/trunk/test/SemaCXX/forbid-temporaries.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/forbid-temporaries.cpp?rev=124217&view=auto
==============================================================================
--- cfe/trunk/test/SemaCXX/forbid-temporaries.cpp (added)
+++ cfe/trunk/test/SemaCXX/forbid-temporaries.cpp Tue Jan 25 14:08:12 2011
@@ -0,0 +1,50 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+#if !__has_attribute(forbid_temporaries)
+#error "Should support forbid_temporaries attribute"
+#endif
+
+class __attribute__((forbid_temporaries)) NotATemporary {
+};
+
+class __attribute__((forbid_temporaries(1))) ShouldntHaveArguments { // expected-error {{attribute requires 0 argument(s)}}
+};
+
+void bad_function() __attribute__((forbid_temporaries)); // expected-warning {{'forbid_temporaries' attribute only applies to classes}}
+
+int var __attribute__((forbid_temporaries)); // expected-warning {{'forbid_temporaries' attribute only applies to classes}}
+
+void bar(const NotATemporary&);
+
+void foo() {
+ NotATemporary this_is_fine;
+ bar(NotATemporary()); // expected-warning {{must not create temporaries of type 'NotATemporary'}}
+ NotATemporary(); // expected-warning {{must not create temporaries of type 'NotATemporary'}}
+}
+
+
+// Check that the above restrictions work for templates too.
+template<typename T>
+class __attribute__((forbid_temporaries)) NotATemporaryTpl {
+};
+
+template<typename T>
+void bar_tpl(const NotATemporaryTpl<T>&);
+
+void tpl_user() {
+ NotATemporaryTpl<int> this_is_fine;
+ bar_tpl(NotATemporaryTpl<int>()); // expected-warning {{must not create temporaries of type 'NotATemporaryTpl<int>'}}
+ NotATemporaryTpl<int>(); // expected-warning {{must not create temporaries of type 'NotATemporaryTpl<int>'}}
+}
+
+
+// Test that a specialization can override the template's default.
+struct TemporariesOk;
+template<> class NotATemporaryTpl<TemporariesOk> {
+};
+
+void specialization_user() {
+ NotATemporaryTpl<TemporariesOk> this_is_fine;
+ bar_tpl(NotATemporaryTpl<TemporariesOk>());
+ NotATemporaryTpl<TemporariesOk>();
+}
More information about the cfe-commits
mailing list