Auto merge of #158943 - Albab-Hasan:expect-derive-cfg-experiment, r=<try>

fulfill `#[expect]` expectations from derive generated code

Author: bors

compiler/rustc_lint/src/levels.rs

@@ -1,5 +1,5 @@
-// Make sure that the copied `#[expect]` attr in the derived code does not trigger an unfulfilled
-// expectation as it's linked to the original one which is fulfilled.
+// Make sure that sharing the `#[expect]` attr with the derived code does not trigger an
+// unfulfilled expectation there when the expectation is fulfilled at the original item.
 //
 // See <https://github.com/rust-lang/rust/issues/150553#issuecomment-3780810363> for rational.
 

tests/ui/lint/rfc-2383-lint-reason/derive-expect-issue-150553-2.rs

@@ -1,13 +1,11 @@
-// FIXME: Bring back duplication of the `#[expect]` attribute when deriving.
-//
-// Make sure we produce the unfulfilled expectation lint if neither the struct or the
-// derived code fulfilled it.
+// Make sure we produce the unfulfilled expectation lint exactly once if neither the
+// struct nor the derived code fulfilled it: one written attribute is one expectation,
+// no matter how many impls are derived from the item.
 
 //@ check-pass
 
 #[expect(unexpected_cfgs)]
 //~^ WARN this lint expectation is unfulfilled
-//FIXME ~^^ WARN this lint expectation is unfulfilled
 #[derive(Debug)]
 pub struct MyStruct {
     pub t_ref: i64,

tests/ui/lint/rfc-2383-lint-reason/derive-expect-issue-150553-3.rs

@@ -1,5 +1,5 @@
 warning: this lint expectation is unfulfilled
-  --> $DIR/derive-expect-issue-150553-3.rs:8:10
+  --> $DIR/derive-expect-issue-150553-3.rs:7:10
    |
 LL | #[expect(unexpected_cfgs)]
    |          ^^^^^^^^^^^^^^^

tests/ui/lint/rfc-2383-lint-reason/derive-expect-issue-150553-3.stderr

@@ -0,0 +1,25 @@
+// An `#[expect]` on an item is shared with the impls derived from it, but not with
+// hand-written impls for the same type: lints there must still fire.
+
+#![deny(redundant_lifetimes)]
+
+#[derive(Clone)]
+#[expect(redundant_lifetimes)]
+pub struct W<'a>
+where
+    'a: 'static,
+{
+    pub r: &'a u8,
+}
+
+impl<'a> W<'a>
+//~^ ERROR unnecessary lifetime parameter `'a`
+where
+    'a: 'static,
+{
+    pub fn get(&self) -> &'a u8 {
+        self.r
+    }
+}
+
+fn main() {}

tests/ui/lint/rfc-2383-lint-reason/derive-expect-issue-150553-5.rs

@@ -1,12 +1,12 @@
 error: unnecessary lifetime parameter `'a`
-  --> $DIR/derive-expect-issue-150553.rs:16:23
+  --> $DIR/derive-expect-issue-150553-5.rs:15:6
    |
-LL | pub struct RefWrapper<'a, T>
-   |                       ^^
+LL | impl<'a> W<'a>
+   |      ^^
    |
    = note: you can use the `'static` lifetime directly, in place of `'a`
 note: the lint level is defined here
-  --> $DIR/derive-expect-issue-150553.rs:10:9
+  --> $DIR/derive-expect-issue-150553-5.rs:4:9
    |
 LL | #![deny(redundant_lifetimes)]
    |         ^^^^^^^^^^^^^^^^^^^

…reason/derive-expect-issue-150553.stderr …ason/derive-expect-issue-150553-5.stderrtests/ui/lint/rfc-2383-lint-reason/derive-expect-issue-150553.stderr renamed to tests/ui/lint/rfc-2383-lint-reason/derive-expect-issue-150553-5.stderr tests/ui/lint/rfc-2383-lint-reason/derive-expect-issue-150553.stderr renamed to tests/ui/lint/rfc-2383-lint-reason/derive-expect-issue-150553-5.stderr

@@ -0,0 +1,44 @@
+// The `#[expect]` sharing with derived code must survive `#[cfg]`/`#[cfg_attr]`
+// processing of the derive input: the attribute-id duplication this caused is why
+// #152289 (copying the attribute to the derived impl) was reverted in #153055.
+// One written attribute is one expectation, fulfilled by the item or its derived
+// code, and reported exactly once when genuinely unfulfilled.
+
+//@ check-pass
+
+#![deny(redundant_lifetimes)]
+
+use std::fmt::Debug;
+
+#[derive(Debug)]
+#[expect(redundant_lifetimes)]
+pub struct CfgField<'a, T: Debug>
+where
+    'a: 'static,
+{
+    pub t_ref: &'a T,
+    #[cfg(false)]
+    pub gone: u8,
+}
+
+#[derive(Debug)]
+#[cfg_attr(all(), expect(redundant_lifetimes))]
+pub struct CfgAttrExpect<'a, T: Debug>
+where
+    'a: 'static,
+{
+    pub t_ref: &'a T,
+    #[cfg(false)]
+    pub gone: u8,
+}
+
+#[derive(Debug)]
+#[expect(unexpected_cfgs)]
+//~^ WARN this lint expectation is unfulfilled
+pub struct Unfulfilled {
+    pub x: i64,
+    #[cfg(false)]
+    pub gone: u8,
+}
+
+fn main() {}

tests/ui/lint/rfc-2383-lint-reason/derive-expect-issue-150553-6.rs

@@ -0,0 +1,10 @@
+warning: this lint expectation is unfulfilled
+  --> $DIR/derive-expect-issue-150553-6.rs:36:10
+   |
+LL | #[expect(unexpected_cfgs)]
+   |          ^^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(unfulfilled_lint_expectations)]` on by default
+
+warning: 1 warning emitted
+

tests/ui/lint/rfc-2383-lint-reason/derive-expect-issue-150553-6.stderr

@@ -0,0 +1,57 @@
+// The `#[expect]` sharing with derive-generated code also applies when the
+// derive itself is expanded from a macros 2.0 macro: the derive expansion is
+// the innermost one, so the expansion-kind gate recognizes the impl no matter
+// what macro produced the derived item. A genuinely unfulfilled expectation
+// is still reported exactly once.
+
+//@ check-pass
+
+#![feature(decl_macro)]
+#![deny(redundant_lifetimes)]
+
+use std::fmt::Debug;
+
+macro fulfilled() {
+    #[derive(Debug)]
+    #[expect(redundant_lifetimes)]
+    pub struct RefWrapper<'a, T>
+    where
+        'a: 'static,
+        T: Debug,
+    {
+        pub t_ref: &'a T,
+    }
+}
+
+fulfilled!();
+
+macro passthrough($i:item) {
+    $i
+}
+
+passthrough! {
+    #[derive(Debug)]
+    #[expect(redundant_lifetimes)]
+    pub struct RefWrapperPassthrough<'a, T>
+    where
+        'a: 'static,
+        T: Debug,
+    {
+        pub t_ref: &'a T,
+    }
+}
+
+macro unfulfilled() {
+    #[derive(Debug)]
+    #[expect(unexpected_cfgs)]
+    //~^ WARN this lint expectation is unfulfilled
+    pub struct Unfulfilled {
+        pub x: i64,
+        #[cfg(false)]
+        pub gone: u8,
+    }
+}
+
+unfulfilled!();
+
+fn main() {}

tests/ui/lint/rfc-2383-lint-reason/derive-expect-issue-150553-7.rs

@@ -0,0 +1,14 @@
+warning: this lint expectation is unfulfilled
+  --> $DIR/derive-expect-issue-150553-7.rs:46:14
+   |
+LL |     #[expect(unexpected_cfgs)]
+   |              ^^^^^^^^^^^^^^^
+...
+LL | unfulfilled!();
+   | -------------- in this macro invocation
+   |
+   = note: `#[warn(unfulfilled_lint_expectations)]` on by default
+   = note: this warning originates in the macro `unfulfilled` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+warning: 1 warning emitted
+