Commit fdccb42

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Add test/comment about const patterns with unused params

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Lines changed: 6 additions & 0 deletions

Original file line number	Diff line number	Diff line change
`@@ -625,6 +625,12 @@ pub fn try_evaluate_const<'tcx>(`
`625`	`625`	`// So we are free to simply defer evaluation here.`
`626`	`626`	`//`
`627`	`627`	// FIXME: This assumes that `args` are normalized which is not necessarily true
	`628`	`+ //`
	`629`	`+ // Const patterns are converted to type system constants before being`
	`630`	`+ // evaluated. However, we don't care about them here as pattern evaluation`
	`631`	`+ // logic does not go through type system normalization. If it did this would`
	`632`	`+ // be a backwards compatibility problem as we do not enforce "syntactic" non-`
	`633`	`+ // usage of generic parameters like we do here.`
`628`	`634`	`if uv.args.has_non_region_param() \|\| uv.args.has_non_region_infer() {`
`629`	`635`	`return Err(EvaluateConstErr::HasGenericsOrInfers);`
`630`	`636`	`}`

Lines changed: 19 additions & 0 deletions

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,19 @@`
	`1`	`+//@ check-pass`
	`2`	`+`
	`3`	`+// Tests that const patterns that use generic parameters are`
	`4`	`+// allowed if we are still able to evaluate them.`
	`5`	`+`
	`6`	`+trait Trait { const ASSOC: usize; }`
	`7`	`+`
	`8`	`+impl<T> Trait for T {`
	`9`	`+ const ASSOC: usize = 10;`
	`10`	`+}`
	`11`	`+`
	`12`	`+fn foo<T>(a: usize) {`
	`13`	`+ match a {`
	`14`	`+ <T as Trait>::ASSOC => (),`
	`15`	`+ _ => (),`
	`16`	`+ }`
	`17`	`+}`
	`18`	`+`
	`19`	`+fn main() {}`

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