conan.io - header only package

I'm trying to create a simple demo header only library called foo and require it another library called bar.

The structure of foo is this:

foo/include/foo.hpp - just a test header file...

foo/conanfile.py

from conans import ConanFile, CMake

class FooConan(ConanFile):
    name = "foo"
    version = "0.0.1"
    exports = "*"

export it using:

conan export steazzalini/testing

bar/conanfile.txt

[requires]
foo/0.0.1@steazzalini/testing

[generators]
cmake

conan install fails saying:

ERROR: Can't find a 'foo/0.0.1@steazzalini/testing' package for the specified options and settings

- Try to build from sources with "--build foo" parameter
- If it fails, you could try to contact the package author , report your configuration and try to collaborate to support it.

Package configuration:
- Settings:
- Options:

Thanks in advance for the help!

Solution

Just a minor clarification, I guess you meant that library foo is required by bar.

Every package has to be created, even if it is a header only library. When you conan export it copies the source code into the recipe (the other alternative would be using the source() method to retrieve the source code), but the package still has to be created.

The build() method is not necessary, as there is nothing to build, but you should add the package() method to your recipe, something like:

def package(self):
   self.copy("*.h", dst="include", src="include")

Then you have to create the package. This can be done with several methods, one would be to install the foo package:

$ conan install foo/0.0.1@steazzalini/testing --build

But this is typically not necessary, as you can also build it when calling the install from the consumer project (the bar one):

$ conan install . --build

There is also an option, the build_policy that can be added to recipes, and is well suited for header only libraries. It can be missing or always. The latter is useful when creating packages from the latest git (master/head..) commit of a project. Using this policy, the consumers doesn't have to explicitely call --build to specify that the package has to be created. So the recipe could be something like:

from conans import ConanFile, CMake

class FooConan(ConanFile):
    name = "foo"
    version = "0.0.1"
    exports = "*"
    build_policy = "missing"

    def package(self):
       self.copy("*.h", dst="include", src="include")

Finally, you might be interested in the $ conan new foo/0.0.1@steazzalini/testing -i command, that will create a conanfile.py for you with some of these things. The -t option for such command is useful to create a test_package, a utility for creating and testing packages, to ensure the package is correct. Have a look at http://docs.conan.io/en/latest/packaging/testing.html#automatically-creating-and-testing-packages

UPDATE: conan docs got a new section specific for header-only libraries: http://docs.conan.io/en/latest/howtos/header_only.html