Clang tooling namespace issues

Clang Frontend
#1

Hi,

I’m trying to write a clang compiler tool that will change any functions that take an argument of type StringData by const ref to taking it by value. I would like to have the transformed argument have the same naming format as the original (i.e. if it’s declared without a namespace qualifier, then the rewritten argument should not have one and vice versa). StringData is my string wrapper class.

For example, I want to transform:

void example(const StringData& d);

into:

void example(StringData);

And I also want to be able to transform:

void example_ns(const ns::StringData& d);

into:

void example_ns(ns::StringData);

I’m using RecursiveASTVisitor, and in my VisitFunctionDecl function I check for arguments that match my criteria then use the Rewriter class to change the argument from const ref to a value. My problem is that the transformation always writes the full elaborated type, so for const StringData&, instead of changing the argument type to simply StringData, it changes it to class ns::StringData.

My code currently looks like this:

bool VisitFunctionDecl(FunctionDecl *f) {

for (unsigned int i=0; igetNumParams(); i++) {

ParmVarDecl* p = f->getParamDecl(i);

QualType original_type = p->getOriginalType();

QualType original_nr = original_type.getNonReferenceType();

const IdentifierInfo* id = original_type.getBaseTypeIdentifier();

if (id == NULL) { continue; }

if (!id->getName().compare(“StringData”) &&

original_type->isReferenceType() &&

original_nr.isConstQualified()) {

original_nr.removeLocalConst();

TheRewriter.ReplaceText(p->getSourceRange(), original_nr.getAsString());

}

}

return true;
}

If I run this code on the following example:

void example_ns(const ns::StringData& d);

using namespace ns;
void example(const StringData& d);

The result looks like:

void example_ns(ns::StringData);
using namespace ns;
void example(class ns::StringData);

But I want the result to look like:

void example_ns(ns::StringData);

using namespace ns;

void example(StringData);

Is there a way of finding out if a declaration is made with an explicit namespace qualifier? Is there any way to determine what the actual namespace of a type is? How can I extract the name of the argument type in the same format as it’s declared in the original source?

I am also working on another tool for identifying namespace dependencies so any advice involving namespaces and RecursiveASTVisitors is welcome :slight_smile:

Thank you!

Anna

#2

Hi Anna, if StringData is a C++ class you can call getAsCXXRecordDecl on QualType to get the class declaration. Call getQualifier (defined in TagDecl base class) on the declaration to access the NestedNameSpecifier.

#3

Also, your snippet looks light it could profit from the refactoring libs we have in clang.
A nice intro is:
http://eli.thegreenplace.net/2014/07/29/ast-matchers-and-clang-refactoring-tools

#4

Thank you for getting back to me! Unfortunately, when I call getQualifier() on the CXXRecordDecl it always returns null. I tried calling it for my own class, ns::StringData, but also std::String and both cases return null.

I ran:

QualType original_type = p->getOriginalType();

QualType nonref_type = original_type.getNonReferenceType();

nonref_type.removeLocalConst();

CXXRecordDecl* decl = nonref_type->getAsCXXRecordDecl();

NestedNameSpecifier* name = decl->getQualifier();

if( name == NULL ) {
printf(“null name: %s\n”, nonref_type.getAsString().c_str());
}

on:

void std_ns(const std::string& d);

void strdata_ns(const mongo::StringData& d);

name is always NULL. Any suggestions on why this might be happening?

Thank you!

#5

Thank you for getting back to me! Unfortunately, when I call
getQualifier() on the CXXRecordDecl it always returns null. I tried calling
it for my own class, ns::StringData, but also std::String and both cases
return null.

CXXRecordDecl::getQualifier gives you this:

struct ns::Foo {};
       ^^^^

You want ElaboratedType::getQualifier(), which gives you this:

void f(ns::Foo);
       ^^^^

#6

Thank you for the help!! That fixed my problem :slight_smile:

For anybody interested, what ended up working was:

bool VisitFunctionDecl(FunctionDecl *f) {
for (unsigned int i=0; igetNumParams(); i++) {

ParmVarDecl* p = f->getParamDecl(i);
QualType original_type = p->getOriginalType();
QualType original_nr = original_type.getNonReferenceType();
const IdentifierInfo* id = original_type.getBaseTypeIdentifier();
if (id == NULL) { continue; }

if (!id->getName().compare(“StringData”) &&
original_type->isReferenceType() &&
original_nr.isConstQualified()) {

original_nr.removeLocalConst();

Type::TypeClass t = original_nr->getTypeClass();

if( t == Type::Elaborated ) { // if namespace qualified

const ElaboratedType* etype = cast(orignal_nr);

NestedNameSpecifier* name = etype->getQualifier();

name->print(s, Policy);

}

s << id->getName().data();

TheRewriter.ReplaceText(p->getSourceRange(), s.str());

}

}

return true;
}

Note that this works with arguments declared as “const StringData&” and “const ns::StringData&” but not with something like “const class StringData&”.

Thanks again!