Target modifiers (special marked options) are recorded in metainfo

[azhogin]

Target modifiers (special marked options) are recorded in metainfo and compared to be equal in different linked crates.

PR for this RFC: rust-lang/rfcs#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.

[rustbot]

r? @davidtwco

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[azhogin]

@rustbot ready

[saethlin]

@bors r=davidtwco,saethlin

[bors]

📌 Commit 05c88a3 has been approved by davidtwco,saethlin

It is now in the queue for this repository.

[bors]

⌛ Testing commit 05c88a3 with merge 73e2412...

[saethlin]

@bors retry

[bors]

⌛ Testing commit 05c88a3 with merge 7daf4cf...

[bors]

☀️ Test successful - checks-actions
Approved by: davidtwco,saethlin
Pushing 7daf4cf to master...

[rust-timer]

Finished benchmarking commit (7daf4cf): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

This benchmark run did not return any relevant results for this metric.

Cycles

Results (primary 4.5%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	4.5%	[4.5%, 4.5%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	4.5%	[4.5%, 4.5%]	1

Binary size

Results (secondary 0.0%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.0%	[0.0%, 0.0%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Bootstrap: 778.369s -> 779.014s (0.08%)
Artifact size: 328.65 MiB -> 328.74 MiB (0.03%)

[petrochenkov]

The tests are unignored on all platforms in #137801.

[petrochenkov]

Also, the amount of over-engineering in the implementation here is very high.

There will only be several options like this, half of them will likely use some individual approach and smart comparison.
So there's no need to introduce the TARGET_MODIFIER syntax and parse it using elaborated tt munchers.
There's also no need to generalize over various modifiers to put them into a single map or vector.

A structure with a manually written field per every modifier should work well enough here.