no prelude rust example mysteriously fails

[steveklabnik]

If I am in the "no prelude" example directory, building the Rust project works just fine.

buck2\examples\no_prelude〉buck2 build //rust:main
Build ID: 08d04cf1-ec8f-4450-87ec-b5674348fdce
Jobs completed: 3. Time elapsed: 0.0s.
BUILD SUCCEEDED

If I copy that entire subdirectory into a new project:

buck-rust-hello〉git status
On branch main
Changes to be committed:
  (use "git restore --staged <file>..." to unstage)
        modified:   .buckconfig
        new file:   .buckroot
        deleted:    .gitmodules
        modified:   BUCK
        new file:   README.md
        new file:   cpp/hello_world/BUCK
        new file:   cpp/hello_world/func.cpp
        new file:   cpp/hello_world/func.hpp
        new file:   cpp/hello_world/main.cpp
        new file:   cpp/library/BUCK
        new file:   cpp/library/library.cpp
        new file:   cpp/library/library.hpp
        new file:   cpp/rules.bzl
        new file:   go/BUCK
        new file:   go/go_binary.bzl
        new file:   go/main.go
        new file:   go/rules.bzl
        deleted:    prelude
        new file:   prelude.bzl
        new file:   prelude/prelude.bzl
        new file:   rust/BUCK
        new file:   rust/main.rs
        new file:   rust/rules.bzl
        modified:   toolchains/BUCK
        new file:   toolchains/cpp_toolchain.bzl
        new file:   toolchains/export_file.bzl
        new file:   toolchains/go_toolchain.bzl
        new file:   toolchains/rust_toolchain.bzl
        new file:   toolchains/symlink.bat

I get a failure:

buck2\examples\no_prelude〉buck2 build //rust:main
File changed: root//cpp/hello_world
File changed: root//cpp/library
File changed: root//.git/index.lock
70 additional file change events
Action failed: root//rust:main (compile)
Required outputs are missing: Action failed to produce outputs: `buck-out/v2/gen/root/6dd044292ff31ae1/rust/__main__/main`
Reproduce locally: `rustc "--crate-type=bin" "rust\\main.rs" -o "buck-out\\v2\\gen\\root\\6dd044292ff31ae1\\rust\\__main__\\main"`
stdout:
stderr:
Build ID: 0efa591f-0382-4df5-b9a5-bd623bf4a3b5
Jobs completed: 3. Time elapsed: 0.7s. Cache hits: 0%. Commands: 1 (cached: 0, remote: 0, local: 1)
BUILD FAILED
Failed to build 'root//rust:main (<unspecified>)'

Now, why this is failing is very interesting: it's looking for a binary named main, but rustc will be producing one called main.exe. What's extra confusing to me, after scouring all of these rules for the past few hours, is that:

main.exe is being produced by the compiler in the new repo:

buck-rust-hello〉ls buck-out\\v2\\gen\\root\\6dd044292ff31ae1\\rust\\__main__\\
╭───┬──────────────────────────────────────────────────────────────┬──────┬─────────┬──────────────╮
│ # │                             name                             │ type │  size   │   modified   │
├───┼──────────────────────────────────────────────────────────────┼──────┼─────────┼──────────────┤
│ 0 │ buck-out\v2\gen\root\6dd044292ff31ae1\rust\__main__\main.exe │ file │ 5.0 MiB │ a minute ago │
│ 1 │ buck-out\v2\gen\root\6dd044292ff31ae1\rust\__main__\main.pdb │ file │ 1.2 MiB │ 2 hours ago  │
╰───┴──────────────────────────────────────────────────────────────┴──────┴─────────┴──────────────╯

but it is producing main with no extension in the demo sub-repo:

buck2\examples\no_prelude〉ls buck-out\v2\gen\root\6dd044292ff31ae1\rust\__main__\╭───┬──────────────────────────────────────────────────────────────┬──────┬───────────┬─────────────╮
│ # │                             name                             │ type │   size    │  modified   │
├───┼──────────────────────────────────────────────────────────────┼──────┼───────────┼─────────────┤
│ 0 │ buck-out\v2\gen\root\6dd044292ff31ae1\rust\__main__\main     │ file │ 159.5 KiB │ 2 hours ago │
│ 1 │ buck-out\v2\gen\root\6dd044292ff31ae1\rust\__main__\main.pdb │ file │   1.2 MiB │ 2 hours ago │
╰───┴──────────────────────────────────────────────────────────────┴──────┴───────────┴─────────────╯

Does this behavior make sense? Is there some other bit of ambient configuration that I'm missing?

[ndmitchell]

I wouldn't think too hard about the no_prelude rules. The don't use the Prelude rust rules, so they aren't really complete enough to be expected to work.

[steveklabnik]

Yeah, I was just trying to get something going on my local machine, and given that this example does build for me in-tree, was hoping it would be a bit simpler to get started with before trying to figure out what's up with the prelude :)

Given that's a longer-term solution anyways, seems good! I'll not chase down this thread. Thanks :)