rust/compiler/rustc_expand
bors a97c36dd2e Auto merge of #109005 - Nilstrieb:dont-forgor-too-much-from-cfg, r=petrochenkov
Remember names of `cfg`-ed out items to mention them in diagnostics

# Examples

## `serde::Deserialize` without the `derive` feature (a classic beginner mistake)

I had to slightly modify serde so that it uses explicit re-exports instead of a glob re-export. (Update: a serde PR was merged that adds the manual re-exports)

```
error[E0433]: failed to resolve: could not find `Serialize` in `serde`
   --> src/main.rs:1:17
    |
1   | #[derive(serde::Serialize)]
    |                 ^^^^^^^^^ could not find `Serialize` in `serde`
    |
note: crate `serde` has an item named `Serialize` but it is inactive because its cfg predicate evaluated to false
   --> /home/gh-Nilstrieb/.cargo/registry/src/index.crates.io-6f17d22bba15001f/serde-1.0.160/src/lib.rs:343:1
    |
343 | #[cfg(feature = "serde_derive")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
344 | pub use serde_derive::{Deserialize, Serialize};
    |                                     ^^^^^^^^^
    = note: the item is gated behind the `serde_derive` feature
    = note: see https://doc.rust-lang.org/cargo/reference/features.html for how to activate a crate's feature
```
(the suggestion is not ideal but that's serde's fault)

I already tested the metadata size impact locally by compiling the `windows` crate without any features. `800k`  -> `809k`

r? `@ghost`
2023-06-07 17:38:57 +00:00
..
src Auto merge of #109005 - Nilstrieb:dont-forgor-too-much-from-cfg, r=petrochenkov 2023-06-07 17:38:57 +00:00
Cargo.toml Add rustc_fluent_macro to decouple fluent from rustc_macros 2023-04-18 18:56:22 +00:00
messages.ftl Ensure Fluent messages are in alphabetical order 2023-05-25 23:49:35 +00:00