add diagnostic note for #[ffi_pure] with #[ffi_const]

el-ev · el-ev · commit 6efada081d57 · 2026-05-06T20:32:08.000+08:00
diff --git a/compiler/rustc_attr_parsing/src/session_diagnostics.rs b/compiler/rustc_attr_parsing/src/session_diagnostics.rs
@@ -1159,7 +1159,9 @@ pub(crate) enum InvalidMachoSectionReason {
 
 #[derive(Diagnostic)]
 #[diag("`#[ffi_const]` function cannot be `#[ffi_pure]`", code = E0757)]
+#[note("`#[ffi_pure]` is redundant here because `#[ffi_const]` provides stronger guarantees")]
 pub(crate) struct BothFfiConstAndPure {
     #[primary_span]
+    #[suggestion("remove `#[ffi_pure]`", code = "", applicability = "maybe-incorrect")]
     pub attr_span: Span,
 }
diff --git a/tests/ui/ffi-attrs/ffi_const2.stderr b/tests/ui/ffi-attrs/ffi_const2.stderr
@@ -2,7 +2,9 @@ error[E0757]: `#[ffi_const]` function cannot be `#[ffi_pure]`
   --> $DIR/ffi_const2.rs:4:5
    |
 LL |     #[unsafe(ffi_pure)]
-   |     ^^^^^^^^^^^^^^^^^^^
+   |     ^^^^^^^^^^^^^^^^^^^ help: remove `#[ffi_pure]`
+   |
+   = note: `#[ffi_pure]` is redundant here because `#[ffi_const]` provides stronger guarantees
 
 error: aborting due to 1 previous error
 

Original file line number	Diff line number	Diff line change
`@@ -1159,7 +1159,9 @@ pub(crate) enum InvalidMachoSectionReason {`
`1159`	`1159`
`1160`	`1160`	`#[derive(Diagnostic)]`
`1161`	`1161`	#[diag("`#[ffi_const]` function cannot be `#[ffi_pure]`", code = E0757)]
	`1162`	+#[note("`#[ffi_pure]` is redundant here because `#[ffi_const]` provides stronger guarantees")]
`1162`	`1163`	`pub(crate) struct BothFfiConstAndPure {`
`1163`	`1164`	`#[primary_span]`
	`1165`	+ #[suggestion("remove `#[ffi_pure]`", code = "", applicability = "maybe-incorrect")]
`1164`	`1166`	`pub attr_span: Span,`
`1165`	`1167`	`}`
Original file line number	Diff line number	Diff line change
@@ -2,7 +2,9 @@ error[E0757]: `#[ffi_const]` function cannot be `#[ffi_pure]`
`2`	`2`	`--> $DIR/ffi_const2.rs:4:5`
`3`	`3`	`\|`
`4`	`4`	`LL \| #[unsafe(ffi_pure)]`
`5`		`- \| ^^^^^^^^^^^^^^^^^^^`
	`5`	+ \| ^^^^^^^^^^^^^^^^^^^ help: remove `#[ffi_pure]`
	`6`	`+ \|`
	`7`	+ = note: `#[ffi_pure]` is redundant here because `#[ffi_const]` provides stronger guarantees
`6`	`8`
`7`	`9`	`error: aborting due to 1 previous error`
`8`	`10`