CMake: How to tell where transitive dependency is coming from?

Question

I'm in the process of rewriting a legacy CMake setup to use modern features like automatic dependency propagation. (i.e. using things like target_include_directories(<target> PUBLIC <dir>) instead of include_directories(<dir>).) Currently, we manually handle all project dependency information by setting a bunch of global directory properties.

In my testing, I've found a few examples where a target in the new build will link to a library that the old build would not. I'm not linking to it explicitly, so I know this is coming from the target's dependencies, but in order to find which one(s) I have to recursively look through all of the project's CMakeLists.txts, following up the dependency hierarchy until I find one that pulls in the library in question. We have dozens of libraries so this is not a trivial process.

Does CMake provide any way to see, for each target, which of its dependencies were added explicitly, and which ones were propagated through transitive dependencies?

It looks like the --graphviz output does show this distinction, so clearly CMake knows the context internally. However, I'd like to write a tree-like script to show dependency information on the command line, and parsing Graphviz files sounds like both a nightmare and a hack.

As far as I can tell, cmake-file-api does not include this information. I thought the codemodel/target/dependencies field might work, but it lists both local and transitive dependencies mixed together. And the backtrace field of each dependency only ties back to the add_executable/add_library call for the current target.

Answer 1

You can parse dot file generated by graphviz and extract details which you want. Below is sample python script to do that.

import pydot
import sys

graph = pydot.graph_from_dot_file(sys.argv[1])
result = {}

for g in graph:
    # print(g)
    for node in g.get_node_list():
        if node.get("label") != None:
            result[node.get("label")] = []

    for edge in g.get_edges():
        result[g.get_node(edge.get_source())[0].get("label")].append(g.get_node(edge.get_destination())[0].get("label"))

for r in result:
    print(r+":"+",".join(result[r]))

You can also add this script to run from cmake as custom target, so you can call it from you build system. You can find sample cmake project here