Improve error message displayed when a string is used instead of an array for 'authors' in the manifest

[ptdecker]

Problem

Currently, if one uses a string instead of an array of strings as the value for the authors field an error message is displayed which is not helpful for a new Rust developer to identify the cause of the problem.

Example of an incorrect Cargo.toml:

[package]
name = "alenandbarb"
version = "0.1.0"
edition = "2021"
authors = "Todd Decker"
description = "A toy application for crustatian exploration along network and applications seafloor"

[features]
desktop = ["dioxus/desktop"]
web = ["dioxus/web"]

[dependencies]
dioxus = "0.2.4"

The error message displayed is:

Execution failed (exit code 101).
/Users/ptdecker/.cargo/bin/cargo metadata --verbose --format-version 1 --all-features
stdout : error: failed to parse manifest at `/Users/ptdecker/CLionProjects/alenandbarb/Cargo.toml`

Caused by:
  data did not match any variant of untagged enum MaybeWorkspace for key `package.authors`

stderr : 

Proposed Solution

An error message along the lines of the below would be more informative:

Execution failed (exit code 101).
/Users/ptdecker/.cargo/bin/cargo metadata --verbose --format-version 1 --all-features
stdout : error: failed to parse manifest at `/Users/ptdecker/CLionProjects/alenandbarb/Cargo.toml`

Caused by:
  value of `package.authors` is a string, while an array was expected

stderr : 

Notes

I also submitted the PR below to update the Cargo documentation to better explain the requirements of the field:

#10938

@epage saw my post on the forum about my problem (link) and suggested that I also submit an issue to improve the error message itself.

Thank you

P. Todd Decker

[Rustin170506]

For now, I think it's challenging to improve it because the internal error will ignore by MaybeWorkspace.
Also, publish: Option<MaybeWorkspace<VecStringOrBool>> affect by it, you can not get the VecStringOrBool inner error.

[package]
name = "cargo"
version = "0.65.0"
edition = "2021"
license = "MIT OR Apache-2.0"
homepage = "https://crates.io"
repository = "https:/rust-lang/cargo"
documentation = "https://docs.rs/cargo"
readme = "README.md"
description = """
Cargo, a package manager for Rust.
"""
publish = "a"

➜  cargo git:(master) ✗ ./target/debug/cargo test
error: failed to parse manifest at `/Users/rustin/ClionProjects/cargo/Cargo.toml`

Caused by:
  data did not match any variant of untagged enum MaybeWorkspace for key `package.publish`

It should be invalid type: string "a", expected a boolean or vector of strings.

See more: serde-rs/serde#1544.

@epage Do you have any thoughts about how to work around it?

[Rustin170506]

I saw #10944 try to fix it. Maybe it's a good way.