Failed to build sdist when using python first src layout

[messense]

#1185 was merged too soon, opening an issue to track this.

$ maturin sdist -o dist
🍹 Building a mixed python/rust project
🔗 Found pyo3 bindings
🐍 Found CPython 3.10 at /Users/messense/.pyenv/versions/3.10.6/bin/python3
💥 maturin failed
  Caused by: Failed to build source distribution
  Caused by: Failed to add 340 bytes to sdist as /Users/messense/Projects/maturin/test-crates/pyo3-mixed-src/rust/Cargo.toml
  Caused by: paths in archives must be relative when setting path for

It's actually a general issue when Cargo.toml isn't located at the top level directory since we use cargo package --list --allow-dirty to get the list of files that should be included in sdist.

[konstin]

It's actually a general issue when Cargo.toml isn't located at the top level directory since we use cargo package --list --allow-dirty to get the list of files that should be included in sdist.

oh i've never thought about that :/

[messense]

That was partially resolved in #1099 already, so just need a few tweaks to make src layout work.