Conditional Codegen for Messages, Constructors and Events

[SkymanOne]

This PR closes #1231

It allows constructors, messages and events to be conditionally compiled (i.e. have #[cfg(...)] attribute)

Example

/* --Snippet -- */
#[ink(message)]
#[cfg(feature = "foo")]
pub fn another_get(&self) -> String {
    self.value.clone()
}
/* --Snippet -- */

/* --Snippet -- */
#[ink(constructor)]
#[cfg(feature = "another_foo")]
pub fn another_new(val: String) -> Self {
    Self { value: val }
}
/* --Snippet -- */

/* --Snippet -- */
#[ink(event)]
#[cfg(feature = "foo")]
pub struct FeaturedAuctionEchoed {
    auction: Auction,
}
/* --Snippet -- */

[athei]

Just make cure it builds with the feature enabled cargo check --features foo.

[codecov-commenter]

Codecov Report

Merging #1458 (b83f0e6) into master (408a299) will increase coverage by 5.72%.
The diff coverage is 69.56%.

@@            Coverage Diff             @@
##           master    #1458      +/-   ##
==========================================
+ Coverage   64.39%   70.12%   +5.72%     
==========================================
  Files         200      200              
  Lines        6115     6133      +18     
==========================================
+ Hits         3938     4301     +363     
+ Misses       2177     1832     -345     

Impacted Files	Coverage Δ
crates/ink/codegen/src/generator/dispatch.rs	94.54% <ø> (ø)
crates/ink/ir/src/ir/item_impl/mod.rs	86.82% <45.45%> (+19.02%)	⬆️
crates/ink/ir/src/ir/item_mod.rs	89.71% <75.00%> (+27.64%)	⬆️
crates/ink/codegen/src/generator/events.rs	97.29% <100.00%> (+0.03%)	⬆️
crates/ink/ir/src/ir/item_impl/iter.rs	100.00% <100.00%> (ø)
crates/metadata/src/layout/mod.rs	75.63% <0.00%> (-1.69%)	⬇️
crates/allocator/src/bump.rs	86.77% <0.00%> (+0.22%)	⬆️
crates/ink/ir/src/ir/attrs.rs	81.99% <0.00%> (+0.55%)	⬆️
crates/ink/ir/src/ir/item_impl/callable.rs	91.83% <0.00%> (+4.08%)	⬆️
crates/ink/ir/src/ir/trait_def/item/mod.rs	90.08% <0.00%> (+4.95%)	⬆️
... and 21 more

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[SkymanOne]

Just make cure it builds with the feature enabled cargo check --features foo.

Checked. It works

[ascjones]

I believe this does not work

[ascjones]

A more natural place for this would be ir/utils.rs

[ascjones]

I believe this logic is wrong in the case of multiple cfg attributes e.g.

fn main() {
    foo_bar();
}

#[cfg(feature = "foo")]
#[cfg(feature = "bar")]
fn foo_bar() {}

cargo build --features foo -> 🔴
cargo build --features bar -> 🔴
cargo build --features foo,bar -> 🟢

So having separate cfg attrs seems to be the equivalent of #[cfg(all(feature = "foo", feature = "bar"))]

The implementation here is instead #[cfg(any(feature = "foo", feature = "bar"))].

[ascjones]

The logic would be easier to read when expressed e.g. in the form:

pub fn is_code_span_enabled(attrs: &[Attribute]) -> bool {
    attrs
        .iter()
        .filter(|a| a.path.is_ident("cfg"))
        .all(|a| {
            let predicate = &a.tokens.to_token_stream();
            cfg!(predicate)
        })
}

[ascjones]

Does this even work with the token stream? cfg! is a compile time macro.

I've tried it and it doesn't appear to work. Even with the literal cfg!(feature = "foo") it doesn't work for some reason. cfg!(unix) literal does work.

I think we need to rethink the approach here, maybe see whether we can carry those attributes through to the generated code (I know it is everywhere)