[cfe-dev] [PATCH] Add an attribute to forbid temporary instances of a type (issue3745045)
jyasskin at gmail.com
jyasskin at gmail.com
Tue Dec 28 18:00:32 PST 2010
Reviewers: ,
Message:
This is the first attribute I've added, so please let me know about
anything I could have done better.
Current diff at
http://codereview.appspot.com/download/issue3745045_1.diff
Description:
This allows class authors to write "class
__attribute__((no_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.
Please review this at http://codereview.appspot.com/3745045/
Affected files:
M docs/LanguageExtensions.html
include/clang/Basic/Attr.td
M include/clang/Basic/DiagnosticSemaKinds.td
M include/clang/Sema/AttributeList.h
lib/Sema/AttributeList.cpp
lib/Sema/SemaDeclAttr.cpp
lib/Sema/SemaExprCXX.cpp
A test/SemaCXX/no-temporaries.cpp
Index: test/SemaCXX/no-temporaries.cpp
===================================================================
--- test/SemaCXX/no-temporaries.cpp (revision 0)
+++ test/SemaCXX/no-temporaries.cpp (revision 0)
@@ -0,0 +1,23 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+#if !__has_attribute(no_temporaries)
+#error "Should support no_temporaries attribute"
+#endif
+
+class __attribute__((no_temporaries)) NotATemporary {
+};
+
+class __attribute__((no_temporaries(1))) ShouldntHaveArguments { //
expected-error {{attribute requires 0 argument(s)}}
+};
+
+void bad_function() __attribute__((no_temporaries)); // expected-warning
{{'no_temporaries' attribute only applies to class types}}
+
+int var __attribute__((no_temporaries)); // expected-warning
{{'no_temporaries' attribute only applies to class types}}
+
+void bar(const NotATemporary&);
+
+void foo() {
+ NotATemporary this_is_fine;
+ bar(NotATemporary()); // expected-error {{Must not create temporaries
of type 'NotATemporary'}}
+ NotATemporary(); // expected-error {{Must not create temporaries of
type 'NotATemporary'}}
+}
Index: include/clang/Basic/Attr.td
===================================================================
--- include/clang/Basic/Attr.td (revision 122515)
+++ include/clang/Basic/Attr.td (working copy)
@@ -328,6 +328,11 @@
let Subjects = [Function];
}
+def NoTemporaries : Attr {
+ let Spellings = ["no_temporaries"];
+ let Subjects = [CXXRecord];
+}
+
def NoThrow : Attr {
let Spellings = ["nothrow"];
}
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td (revision 122515)
+++ include/clang/Basic/DiagnosticSemaKinds.td (working copy)
@@ -839,6 +839,8 @@
"of type %1 invokes deleted constructor">;
def err_temp_copy_incomplete : Error<
"copying a temporary object of incomplete type %0">;
+def err_no_temporaries_allowed : Error<
+ "Must not create temporaries of type %0">;
// C++0x decltype
def err_cannot_determine_declared_type_of_overloaded_function : Error<
Index: include/clang/Sema/AttributeList.h
===================================================================
--- include/clang/Sema/AttributeList.h (revision 122515)
+++ include/clang/Sema/AttributeList.h (working copy)
@@ -119,6 +119,7 @@
AT_nodebug,
AT_noinline,
AT_no_instrument_function,
+ AT_no_temporaries,
AT_nocommon,
AT_nonnull,
AT_noreturn,
Index: docs/LanguageExtensions.html
===================================================================
--- docs/LanguageExtensions.html (revision 122515)
+++ docs/LanguageExtensions.html (working copy)
@@ -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="#no-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>
@@ -342,6 +343,32 @@
<p>Query for this feature with
<tt>__has_feature(enumerator_attributes)</tt>.</p>
<!--
======================================================================= -->
+<h2 id="no-temporaries-attribute">Attribute to forbid temporaries of a
type</h2>
+<!--
======================================================================= -->
+
+<p>Clang provides a <tt>no_temporaries</tt> attribute to forbid
+temporaries of a particular type.</p>
+
+<blockquote>
+<pre>class __attribute__((no_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(no_temporaries)</tt>.</p>
+
+<!--
======================================================================= -->
<h2 id="checking_language_features">Checks for Standard Language
Features</h2>
<!--
======================================================================= -->
Index: lib/Sema/SemaExprCXX.cpp
===================================================================
--- lib/Sema/SemaExprCXX.cpp (revision 122515)
+++ lib/Sema/SemaExprCXX.cpp (working copy)
@@ -3179,9 +3179,12 @@
}
}
+ CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
+ if (RD->getAttr<NoTemporariesAttr>())
+ Diag(E->getExprLoc(), diag::err_no_temporaries_allowed) <<
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);
Index: lib/Sema/SemaDeclAttr.cpp
===================================================================
--- lib/Sema/SemaDeclAttr.cpp (revision 122515)
+++ lib/Sema/SemaDeclAttr.cpp (working copy)
@@ -860,6 +860,24 @@
d->addAttr(::new (S.Context) VecReturnAttr(Attr.getLoc(), S.Context));
}
+static void HandleNoTemporariesAttr(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) NoTemporariesAttr(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)
@@ -2648,6 +2666,8 @@
HandleOwnershipAttr (D, Attr, S); break;
case AttributeList::AT_naked: HandleNakedAttr (D, Attr, S);
break;
case AttributeList::AT_noreturn: HandleNoReturnAttr (D, Attr, S);
break;
+ case AttributeList::AT_no_temporaries:
+ HandleNoTemporariesAttr(D, Attr, S); break;
case AttributeList::AT_nothrow: HandleNothrowAttr (D, Attr, S);
break;
case AttributeList::AT_override: HandleOverrideAttr (D, Attr, S);
break;
case AttributeList::AT_shared: HandleSharedAttr (D, Attr, S);
break;
Index: lib/Sema/AttributeList.cpp
===================================================================
--- lib/Sema/AttributeList.cpp (revision 122515)
+++ lib/Sema/AttributeList.cpp (working copy)
@@ -118,6 +118,7 @@
.Case("reqd_work_group_size", AT_reqd_wg_size)
.Case("init_priority", AT_init_priority)
.Case("no_instrument_function", AT_no_instrument_function)
+ .Case("no_temporaries", AT_no_temporaries)
.Case("thiscall", AT_thiscall)
.Case("pascal", AT_pascal)
.Case("__cdecl", AT_cdecl)
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