metadata: add --no-deps option

[matklad]

closes #2356. The output is not exactly the same as with read-manifest, because I wanted to include the version field.

Tests and implementation is a copy-paste from read-manifest except that this line is omited, because root_package does update anyway.

[rust-highfive]

r? @huonw

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[matklad]

r? @alexcrichton

[alexcrichton]

Instead of different encodable formats, perhaps we could tweak the existing one to look like:

 pub struct ExportInfo {
     packages: Vec<Package>,
     resolve: Option<MetadataResolve>,
     version: u32,
 } 

That way with --no-deps you'd just have one package in the array and a null resolve?

[matklad]

That way with --no-deps you'd just have one package in the array and a null resolve?

Makes perfect sense, PR updated.

[alexcrichton]

Oh actually, while you're at it, can you change this assertion to a nicer error? For example something along the lines of:

if opt.version != VERSION {
    bail!("metadata version {} not supported, only {} is currently supported", opt.version, VERSION);
}

[alexcrichton]

(and add a test while you're at it)

[matklad]

Huh, I somehow thought that docopt should check the version automatically. Fixed.

[alexcrichton]

@bors: r+ 80e3c05

[bors]

⌛️ Testing commit 80e3c05 with merge ff0d51b...

[bors]

💔 Test failed - cargo-win-msvc-64

[alexcrichton]

@bors: retry

On Fri, Feb 5, 2016 at 12:50 PM, bors notifications@github.com wrote:

[image: 💔] Test failed - cargo-win-msvc-64
http://buildbot.rust-lang.org/builders/cargo-win-msvc-64/builds/296

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#2359 (comment).

[bors]

⌛️ Testing commit 80e3c05 with merge b5e0a45...

[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