Graphml: unnecessary dependency on graphviz (and thus Boost.Regex)

[francoisk]

Context/background

We have packaged Boost for build2 and are about to release changes that reduce the number of dependencies on Boost.Regex.

The way we have done this in our Boost.Graph package is to make the graphviz "submodule"---which is the only part that logically depends on Boost.Regex---optional and disabled by default. When it is disabled none of the graphviz-related headers are installed.

The problem

However, graphml.hpp includes graphviz.hpp, making it impossible to disable graphviz without also disabling graphml, and this for nothing but a few exception structs.

Suggested solution

Our package's patch breaks this dependency by moving these exception structs to exception.hpp (which already contains exceptions that look similar/related to the ones in question) and including exception.hpp from graphml.hpp and graphviz.hpp.

[jeremy-murphy]

Sounds great! Can you make a pull request with your patch here?

[jeremy-murphy]

That Boost.Regex dependency has been a pain for a while, but I haven't had time to look into it.

[boris-kolpackov]

That Boost.Regex dependency has been a pain for a while, but I haven't had time to look into it.

FYI, the direct dependency on Boost.Regex is only half of the problem: a number of other dependencies (I see Boost.Algorithm, Boost.Range, and Boost.Serialization right away) will pull Boost.Regex indirectly. But it's a step in the right direction.

[jeremy-murphy]

That PR was merged, so does that resolve this particular issue?

[francoisk]

Yes it does, thanks!