Change semantics of optional dependencies

[s-ludwig]

Currently, an optional dependency is satisfied once it is available locally. This doesn't allow the user to decide when to use an optional dependency on a per project basis, but rather will always be a per machine decision. The proposed new semantics are to satisfy an optional dependency iff:

• another package in the dependency graph has a non-optional dependency to the same package
• the optional package is explicitly listed in the dub.selections.json file

For the second option, there will also need to be a way to achieve this using the CLI, maybe simply by doing an explicit dub upgrade <name of optional dependency> within the project directory.

[luismarques]

Ah, this was driving me crazy. Finding this issue #361 finally explains the strange behaviors I was seeing, which seemed to be bugs. For what it's worth, I "vote" for this issue, because removing local packages to prevent their use (e.g., unwanted used of vibe.d, resulting in an error that I have two main() functions) is quite user unfriendly.

In any case, is this a bug?

{
    "name": "ddbtest",
    "description": "A test case for ddb.",
    "copyright": "Copyright © 2014, luismarques",
    "authors": ["luismarques"],
    "dependencies": {
        "ddb": "~>0.2.2",
        "vibe-d": "~>0.7.21"
    },
    "subConfigurations": {
        "vibe-d": "v2"
    },
    "configurations": [
        {
            "name": "v1",
            "targetType": "executable",
            "versions": ["v1"]
        },
        {
            "name": "v2",
            "targetType": "executable",
            "versions": ["v2", "VibeDefaultMain"]
        }
    ]
}

$ dub run --config=v1
Fetching vibe-d 0.7.21 (getting selected version)...

That is, I want to declare vibe.d a dependency, but only for configuration v2. Yet, when I try to build configuration v1 it fetches vibe.d, which is fatal in the presence of issue #361.

[s-ludwig]

The correct package description looks like this:

{
    "name": "ddbtest",
    "description": "A test case for ddb.",
    "copyright": "Copyright © 2014, luismarques",
    "authors": ["luismarques"],
    "dependencies": {
        "ddb": "~>0.2.2"
    },
    "configurations": [
        {
            "name": "v1",
            "targetType": "executable",
            "versions": ["v1"]
        },
        {
            "name": "v2",
            "targetType": "executable",
            "dependencies": {
                "vibe-d": "~>0.7.21"
            },
            "versions": ["v2", "VibeDefaultMain"]
        }
    ]
}

"subConfigurations" selects the configuration used for the dependency, not the configuration in which the dependency is used. But for the latter case, you can also declare a "dependencies" field inside of a configuration.