Strange error message with features on dependencies

[ExpHP]

Problem

cargo build produces a bizarre error message in a workspace with many generated internal dependencies, with features that activate features on their internal dependencies.

I've actually had this issue for a long time (a year?), but my prior attempts to minimize the code ended up causing the bug to disappear! Today I finally succeeded by making a very conservative minimization.

Steps

1. Download: cargo-strange-error.tar.gz.
2. The minimize branch will already be checked out. Run cargo build:

error: failed to select a version for `rsp2-array-types`.
    ... required by package `rsp2 v0.1.0 (/home/lampam/cpp/throwaway/cargo-strange-error)`
versions that meet the requirements `= 0.1.0` are: 0.1.0

the package `rsp2` depends on `rsp2-array-types`, with features: `rsp2-assert-close` but `rsp2-array-types` does not have these features.

3. Observe that rsp2-assert-close never appears as a feature name in any Cargo.toml file. The error message is clearly nonsense!

rg '["/]rsp2-assert-close"'

Bonus round!

Here is an additional thing you can do that may help debug the issue:

Additional repro case

Now try checking out the master branch. This is the code prior to minimization. Observe the following:

• On this branch, cargo build successfully begins building. (Just ctrl-c it; it will take a long time)
• ...but now cargo build --features=nightly produces the exact same error message as above!

The only differences between minimize and master that I would imagine should affect cargo are the removal of build scripts, binaries, integration tests, and the changes listed here (which are mostly just removing external dependencies):

git diff master..minimize -- $(find . -name Cargo.toml)

Notes

The Cargo.toml files in this workspace contain some intimidating-looking [features] that look like this:

nightly = ["beta", "rsp2-array-types/nightly", "rsp2-array-utils/nightly", "rsp2-assert-close/nightly", "rsp2-minimize/nightly", "rsp2-newtype-indices/nightly", "rsp2-structure-io/nightly", "rsp2-structure/nightly", "rsp2-util-macros/nightly"]
beta = ["rsp2-array-types/beta", "rsp2-array-utils/beta", "rsp2-assert-close/beta", "rsp2-minimize/beta", "rsp2-newtype-indices/beta", "rsp2-structure-io/beta", "rsp2-structure/beta", "rsp2-util-macros/beta"]

These lines are programmatically generated. beta activates the /beta feature of every path dependency. nightly activates beta and the /nightly feature of every path dependency.

Cargo version

Tested on:

cargo 1.32.0 (8610973aa 2019-01-02)
cargo 1.36.0-nightly (759b6161a 2019-05-06)

[ehuss]

I think this is the same as #6915. There's something weird about passing a feature through to a dev-dependency.

[ExpHP]

Yep. I tried moving all of my internal dev-dependencies to regular dependencies and the error vanishes.

(well, a different error appears, but one that is correct; "rsp2-structure" mistakenly activates "rsp2-array-types/serde" instead of "rsp2-array-types/serde-support")