Target modifiers (special marked options) are recorded in metainfo
Target modifiers (special marked options) are recorded in metainfo and compared to be equal in different linked crates.
PR for this RFC: https://github.com/rust-lang/rfcs/pull/3716
Option may be marked as `TARGET_MODIFIER`, example: `regparm: Option<u32> = (None, parse_opt_number, [TRACKED TARGET_MODIFIER]`.
If an TARGET_MODIFIER-marked option has non-default value, it will be recorded in crate metainfo as a `Vec<TargetModifier>`:
```
pub struct TargetModifier {
pub opt: OptionsTargetModifiers,
pub value_name: String,
}
```
OptionsTargetModifiers is a macro-generated enum.
Option value code (for comparison) is generated using `Debug` trait.
Error example:
```
error: mixing `-Zregparm` will cause an ABI mismatch in crate `incompatible_regparm`
--> $DIR/incompatible_regparm.rs:10:1
|
LL | #![crate_type = "lib"]
| ^
|
= help: the `-Zregparm` flag modifies the ABI so Rust crates compiled with different values of this flag cannot be used together safely
= note: `-Zregparm=1` in this crate is incompatible with `-Zregparm=2` in dependency `wrong_regparm`
= help: set `-Zregparm=2` in this crate or `-Zregparm=1` in `wrong_regparm`
= help: if you are sure this will not cause problems, use `-Cunsafe-allow-abi-mismatch=regparm` to silence this error
error: aborting due to 1 previous error
```
`-Cunsafe-allow-abi-mismatch=regparm,reg-struct-return` to disable list of flags.
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