Clang-Change-Namespace — Extra Clang Tools 22.1.1 documentation

# Extra Clang Tools 22.1.1 documentation

## Clang-Change-Namespace

clang-change-namespace can be used to change the surrounding namespaces of class/function definitions.

Classes/functions in the moved namespace will have new namespaces while references to symbols (e.g. types, functions) which are not defined in the changed namespace will be correctly qualified by prepending namespace specifiers before them. This will try to add shortest namespace specifiers possible.

When a symbol reference needs to be fully-qualified, this adds a :: prefix to the namespace specifiers unless the new namespace is the global namespace. For classes, only classes that are declared/defined in the given namespace in specified files will be moved: forward declarations will remain in the old namespace. The will be demonstrated in the next example.

## Example usage

For example, consider this test.cc example here with the forward declared class FWD and the defined class A, both in the namespace a.

    namespace a {
    class FWD;
    class A {
      FWD *fwd;
    };
    } // namespace a

And now let’s change the namespace a to x.

    clang-change-namespace \
      --old_namespace "a" \
      --new_namespace "x" \
      --file_pattern "test.cc" \
      --i \
      test.cc

Note that in the code below there’s still the forward decalred class FWD that stayed in the namespace a. It wasn’t moved to the new namespace because it wasn’t defined/declared here in a but only forward declared.

    namespace a {
    class FWD;
    } // namespace a
    namespace x {

    class A {
      a::FWD *fwd;
    };
    } // namespace x

## Another example

Consider this test.cc file:

    namespace na {
    class X {};
    namespace nb {
    class Y {
      X x;
    };
    } // namespace nb
    } // namespace na

To move the definition of class Y from namespace na::nb to x::y, run:

    clang-change-namespace \
      --old_namespace "na::nb" \
      --new_namespace "x::y" \
      --file_pattern "test.cc" \
      --i \
      test.cc

This will overwrite test.cc to look like this:

    namespace na {
    class X {};

    } // namespace na
    namespace x {
    namespace y {
    class Y {
      na::X x;
    };
    } // namespace y
    } // namespace x

Note, that we’ve successfully moved the class Y from namespace na::nb to namespace x::y.

### Caveats

## Content already exists in new namespace

Consider this test.cc example that defines two class A one inside the namespace a and one in namespace b:

    namespace a {
    class A {
        int classAFromWithinNamespace_a;
    };
    } // namespace a

    namespace b {
    class A {
        int classAFromWithinNamespace_b;
    };
    } //namespace b

Let’s move everything from namespace a to namespace b:

    clang-change-namespace \
      --old_namespace "a" \
      --new_namespace "b" \
      --file_pattern test.cc \
      test.cc

As expected we now have to definitions of class A inside the namespace b:

    namespace b {
    class A {
      int classAFromWithinNamespace_a;
    };
    } // namespace b

    namespace b {
    class A {
        int classAFromWithinNamespace_b;
    };
    } //namespace b

The re-factoring looks correct but the code will not compile due to the name duplication. It is not up to the tool to ensure compilability in that sense. But one has to be aware of that.

## Inline namespace doesn’t work

Consider this usage of two versions of implementations for a greet function:

    #include <cstdio>

    namespace Greeter {
    inline namespace Version1 {
      const char* greet() { return "Hello from version 1!"; }
    } // namespace Version1
    namespace Version2 {
      const char* greet() { return "Hello from version 2!"; }
    } // namespace Version2
    } // namespace Greeter

    int main(int argc, char* argv[]) {
      printf("%s\n", Greeter::greet());
      return 0;
    }

Note, that currently Greeter::greet() will result in a call to Greeter::Version1::greet() because that’s the inlined namespace.

Let’s say you want to move one and make Version2 the default now and remove the inline from the Version1. First let’s try to turn namespace Version2 into inline namespace Version2:

    clang-change-namespace \
      --old_namespace "Greeter::Version2" \
      --new_namespace "inline Version2" \
      --file_pattern main.cc main.cc

But this will put the inline keyword in the wrong place resulting in:

    #include <cstdio>

    namespace Greeter {
    inline namespace Version1 {
            const char* greet() { return "Hello from version 1!"; }
    } // namespace Version1

    } // namespace Greeter
    namespace inline Greeter {
    namespace Version2 {
    const char *greet() { return "Hello from version 2!"; }
    } // namespace Version2
    } // namespace inline Greeter

    int main(int argc, char* argv[]) {
            printf("%s\n", Greeter::greet());
            return 0;
    }

One cannot use :program:`clang-change-namespace to inline a namespace.

## Symbol references not updated

Consider this test.cc file:

    namespace old {
    struct foo {};
    }  // namespace old

    namespace b {
    old::foo g_foo;
    }  // namespace b

Notice that namespace b defines a global variable of type old::foo. If we now change the name of the old namespace to modern, the reference will not be updated:

    clang-change-namespace \
      --old_namespace "old" \
      --new_namespace "modern" \
      --file_pattern test.cc \
      test.cc

    namespace modern {
    struct foo {};
    } // namespace modern

    namespace b {
    old::foo g_foo;
    }  // namespace b

g_foo is still of the no longer existing type old::foo while instead it should use modern::foo.

Only symbol references in the moved namespace are updated, not outside of it.

### clang-change-namespace Command Line Options

--allowed_file=<string>

  A file containing regexes of symbol names that are not expected to be updated when changing namespaces around them.

--dump_result

  Dump new file contents in YAML, if specified.

--extra-arg=<string>

  Additional argument to append to the compiler command line

--extra-arg-before=<string>

  Additional argument to prepend to the compiler command line

--file_pattern=<string>

  Only rename namespaces in files that match the given regular expression pattern.

-i

  Inplace edit <file>s, if specified.

--new_namespace=<string>

  New namespace. Use “” when you target the global namespace.

--old_namespace=<string>

  Old namespace.

-p <string>

  Build path

--style=<string>

  The style name used for reformatting.