refactor Target serialization

[matklad]

@alexcrichton another preparation PR for #2196

I've removed obscure metadata field from Target. It is a breaking change (for read-manifest), but the field seemed cryptic, useless and untested :)

Target has a bunch of boolean fields:

    tested: bool,
    benched: bool,
    doc: bool,
    doctest: bool,
    harness: bool, // whether to use the test harness (--test)
    for_host: bool,

I guess they should not be included in serialized representation?

I will push commits for other Encodables here.

[rust-highfive]

r? @huonw

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[matklad]

r? @alexcrichton

[matklad]

I'm not sure what fields of dependency should I serialize:

pub struct DependencyInner {
    name: String, // already included
    source_id: SourceId, // should be included, but is `source_id` a good name? Maybe just `source`?
    req: VersionReq, // already included
    specified_req: Option<String>, // no sure about this one
    kind: Kind, // should be included?
    only_match_name: bool, // should be omitted

    optional: bool, // should be included
    default_features: bool, // should be omitted
    features: Vec<String>, // should be omitted

    // This dependency should be used only for this platform.
    // `None` means *all platforms*.
    only_for_platform: Option<String>, // should be omitted
}

Otherwise I'm ready to merge this

[alexcrichton]

Instead of using a regex for this, could this use .split_whitespace().collect()?

[alexcrichton]

I think it's ok to leave out the other Target fields for now, they generally meant for somewhat niche configurations that Cargo itself is likely the only one to care about.

For dependency information, here's what I think should happen:

pub struct DependencyInner {
    name: String, // include
    source_id: SourceId, // include (naming 'source' is fine)
    req: VersionReq, // include
    specified_req: Option<String>, // omit
    kind: Kind, // include
    only_match_name: bool, // omit

    optional: bool, // include
    default_features: bool, // include
    features: Vec<String>, // include

    only_for_platform: Option<String>, // include, probably call 'target'
}
``

[matklad]

only_for_platform: Option, // include, probably call 'target'

Should I make a custom encodable for this? Or "target": null, is clear enough. The custom encodable could do "target": "all_platforms",

[matklad]

Ok, I think this is done. It has about 0 tests, but I hope to improve this situation in the metadata PR =)

[alexcrichton]

This may want to just be called "dev" as that's what it's called in the manifest

[alexcrichton]

target encoding as null sounds good to me, just a few last nits and should be good to go!

[matklad]

@alexcrichton updated

[alexcrichton]

@bors: r+ 77e7273

[bors]

⌛ Testing commit 77e7273 with merge 3775b3f...

[bors]

☀️ Test successful - cargo-linux-32, cargo-linux-64, cargo-mac-32, cargo-mac-64, cargo-win-gnu-32, cargo-win-gnu-64, cargo-win-msvc-32, cargo-win-msvc-64