Duplicate lang item in crate `core`

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1

I have a workspace with 3 members, a binary "BIN" that depends on one lib "LIB_A" that depends on lib "LIB_B".

They are all no_std. I can currently compile and run my program on my device. I wanted to see if I could work with alloc but as soon as I simply added extern crate alloc, building generates this error:

   Compiling LIB_B v0.1.0 (/Users/me/Documents/project/LIB_B)
error[E0152]: duplicate lang item in crate `core` (which `alloc` depends on): `sized`.
  |
  = note: the lang item is first defined in crate `core` (which `LIB_B` depends on)
  = note: first definition in `core` loaded from /Users/me/Documents/project/target/riscv32imc-unknown-none-elf/release/deps/libcore-54eb2ad189681e1d.rmeta
  = note: second definition in `core` loaded from /Users/me/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/riscv32imc-unknown-none-elf/lib/libcore-17d8084b0bca7cc0.rlib

Adding extern crate alloc is the ONLY difference between compiling+running and this error. I cannot figure out how to fix this. I've tried cleaning, deleting cargo.lock, ran rustup update.

I am compiling for an esp32-c3 (riscv32imac-unknown-none-elf)

config.toml

[target.riscv32imc-unknown-none-elf]
runner = "espflash flash --monitor"

[build]
rustflags = [
  "-C", "link-arg=-Tlinkall.x",
  "-C", "force-frame-pointers",
]

target = "riscv32imc-unknown-none-elf"

[unstable]
build-std = ["core"]

in the BIN folder, rust-toolchain.toml

[toolchain]
channel = "nightly"
components = ["rust-src"]
targets = ["riscv32imc-unknown-none-elf"]

The other workspace members do not have a rust-toolchain.toml file.

2

Did you try including alloc in build-std?

[unstable]
build-std = ["core", "alloc"]
3

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