Workspace `exclude` doesn't work if nested under a `member` path

[acfoltzer]

Problem

It doesn't appear as though the workspace.exclude key works for paths that are nested under a path included in workspace.members

Steps

1. Create a nested package structure:

/tmp % cargo new outer
     Created binary (application) `outer` package
/tmp % cd outer
/tmp/outer % cargo new middle      
     Created binary (application) `middle` package
/tmp/outer % cd middle
/tmp/outer/middle % cargo new inner
     Created binary (application) `inner` package

2. Add a workspace.members key to the outermost level, and observe that the workspace build succeeds:

/tmp/outer/middle % cd /tmp/outer
/tmp/outer % echo "[workspace]\n  members = [\".\", \"middle\"]" >> Cargo.toml
/tmp/outer % cargo build --all
   Compiling middle v0.1.0 (/tmp/outer/middle)                                                                                                                                                                                                                                            
   Compiling outer v0.1.0 (/tmp/outer)                                                                                                                                                                                                                                                    
    Finished dev [unoptimized + debuginfo] target(s) in 0.34s

3. Now go to the inner package and observe that the build fails:

/tmp/outer % cd /tmp/outer/middle/inner 
/tmp/outer/middle/inner % cargo build
error: current package believes it's in a workspace when it's not:
current:   /tmp/outer/middle/inner/Cargo.toml
workspace: /tmp/outer/Cargo.toml

this may be fixable by adding `middle/inner` to the `workspace.members` array of the manifest located at: /tmp/outer/Cargo.toml

4. Fair enough; let's explicitly exclude this package instead, and try again:

/tmp/outer/middle/inner % cd /tmp/outer
/tmp/outer % echo "exclude = [\"middle/inner\"]" >> Cargo.toml
/tmp/outer % cd /tmp/outer/middle/inner
/tmp/outer/middle/inner % cargo build
error: current package believes it's in a workspace when it's not:
current:   /tmp/outer/middle/inner/Cargo.toml
workspace: /tmp/outer/Cargo.toml

this may be fixable by adding `middle/inner` to the `workspace.members` array of the manifest located at: /tmp/outer/Cargo.toml

It still wants to be in the workspace! We're stuck.

Possible Solution(s)

If there's overlap between paths in members and exclude, I would expect the more-specific path to win. In this case, the excluded path "middle/inner" is more specific than the member paths "." or "middle", so the exclusion should win. This is probably not so simple if the paths contain globs, though.

Notes

Output of cargo version:

% cargo version
cargo 1.31.0 (339d9f9c8 2018-11-16)

Thanks for your looking into this 🦀

[ehuss]

As a workaround, in "inner" you can include an empty [workspace] table, and it will work.

I definitely see some wonkiness with checking paths "starts_with".

[acfoltzer]

Yeah, that's the workaround I'm using for now; I can imagine situations where it will be painful to change the inner package, though.

[Michael-F-Bryan]

I just encountered this when creating a dummy crate inside my examples/ directory and originally thought it had something to do with #6009.

The crate is only ever meant to be compiled as WASM so I don't want to include it in the normal workspace. Fortunately I have control over the source code so I can use the workaround proposed by @ehuss for now.

[felipesere]

In my case the top-most Cargo.toml has:

[workspace]
members = [".", "crates/*", "commands/*"]
default-members = [".", "crates/*", "commands/*"]

and I want to exclude crates/README.md and commands/README.md with

exclude = ["crates/README.md", "commands/README.md"]

but I get failures that

$ cargo build                                                                                                                                        
error: failed to read `/Users/felipesere/Development/rust/orogene/crates/README.md/Cargo.toml`

Caused by:
  Not a directory (os error 20)

I was expecting anything listed in exclude (whether its heardcoded or a glob) to be removed from the members

[iitalics]

Any chances this bug can be resolved, or are there any workarounds? Currently running into this problem since I want to create a binary for testing, and put it under the directory for the library it tests.