Pallet without try-runtime feature flag produces a compiler warning

[shawntabrizi]

Ran into this while making some tutorial content:

warning: unexpected `cfg` condition value: `try-runtime`
  --> src/lib.rs:11:12
   |
11 |     #[pallet::pallet]
   |               ^^^^^^
   |
   = note: expected values for `feature` are: `default`, `std`
   = help: consider adding `try-runtime` as a feature in `Cargo.toml`
   = note: see <https://doc.rust-lang.org/nightly/cargo/reference/build-scripts.html#rustc-check-cfg> for more information about checking conditional configuration
   = note: `#[warn(unexpected_cfgs)]` on by default

warning: `pallet-kitties` (lib) generated 1 warning

This is reproducible by taking a pallet without try-runtime feature in the Cargo.toml, and then running:

cargo +nightly build

The solution can be to add try-runtime = [] in the features, but probably better this is fixed within the macros and pallet code.

[gui1117]

I'm on it.

Also we could introduce 2 new attribute macros in frame-support:

• #[cfg_feature_try_runtime]
• and #[cfg_feature_runtime_benchmarks].

User could use them to have some code discarded/included depending on whether frame-support has try-runtime or runtime-benchmarks features.

This would allow people not to have to bother adding try-runtime nor runtime-benchmarks in their Cargo.toml for their pallet.
And avoid some miss when configuring the runtime as well.

If I'm correct runtime crate would only need:

runtime-benchmarks = [
	"frame-support/runtime-benchmarks",
]
try-runtime = [
	"frame-support/try-runtime",
]