About how to add an attribute to clang on the 14th day of llvm

The content is mainly from the document "Clang" CFE internals manual address: Workshop. I am not talking about it here. I just want to combine some of the code and documents in this example to present them to you. How to add an Attribute before ¶

To add an attribute, you'll have to add it to the list of attributes, add it tothe parsing phase, and look for it in the ast scan. r124217 has a good example
Of adding a warning attribute.

(Beware that this hasn't been reviewed/fixed by the people who designed theattributes system yet .)

Include/clang/basic/ATTR. TD

First, add your attribute to
Include/clang/basic/ATTR. TD file.

Each attribute getsDefInheriting fromATTROr one of itssubclasses.Inheritableattr
Means that the attribute also applies tosubsequent declarations of the same name.

SpellingsLists the strings that can appear in_ Attribute _ (here ))Or[[Here].
All such strings will be synonymous. If you want to allow[[]C ++ 11 syntax, You have to define a listNamespaces, Which willlet users
Write[[Namespace: spelling]. Using the empty string for anamespace will allow users to write just the spelling with no"::". Attributes which
G ++-4.8 accepts shoshould also haveCxx11 <"GNU", "spelling">Spelling.

SubjectsRestricts what kinds of AST node to which this attribute canappertain (roughly, attach ).

ARGsNames the arguments the attribute takes, in order. IfARGsIs
[Stringargument <"arg1">,
Intargument <"arg2">]Then_ Attribute _ (myattribute ("hello", 3 )))Will be a valid use.

--- cfe/trunk/include/clang/Basic/Attr.td2011/01/25 19:39:31124216+++ cfe/trunk/include/clang/Basic/Attr.td2011/01/25 20:08:12124217@@ -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">,

Boilerplate

Write a newHandleyourattr ()Function inlib/SEMA/semadeclattr. cpp, and
Add a case to the switch inProcessnoninheritabledeclattr ()Or
Processinheritabledeclattr ()Forwarding to it.

If your attribute causes extra warnings to fire, define
DiaggroupIn
Include/clang/basic/diagnosticgroups. TD named after the attribute's
SpellingWith "_" S replaced by "-" S. If you're 'reonly defining one diagnostic, you can skip Diagnosticgroups. TDAnd use Ingroup <diaggroup <"Your-attribute">
Directly indiagnosticsemakinds. TD

--- cfe/trunk/lib/Sema/SemaDeclAttr.cpp2011/01/25 19:39:31124216+++ cfe/trunk/lib/Sema/SemaDeclAttr.cpp2011/01/25 20:08:12124217@@ -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;

The meat of your attribute

Find an appropriate place in clang to do whatever your attribute needs to do. Check for the attribute's presence usingDecl: getattr <yourattr> ().

Update
Clang language extensionsDocument to describe your new attribute.