Add UI tests for the expect attribute (RFC-2383)

* Add UI tests with macros for the `expect` attribute (RFC-2383)
* Addressed review comments - mostly UI test updates (RFC-2383)
* Documented lint level attribute on macro not working bug (RFC-2383)
  See `rust#87391`

Author: xFrednet

compiler/rustc_lint/src/expect.rs

@@ -16,11 +16,9 @@ pub fn check_expectations(tcx: TyCtxt<'_>) {
         &tcx.lint_levels(()).lint_expectations;
 
     for (id, expectation) in lint_expectations {
-        if fulfilled_expectations.contains(id) {
-            continue;
+        if !fulfilled_expectations.contains(id) {
+            emit_unfulfilled_expectation_lint(tcx, expectation);
         }
-
-        emit_unfulfilled_expectation_lint(tcx, expectation);
     }
 }
 

src/test/ui/lint/rfc-2383-lint-reason/catch_multiple_lint_triggers.rs

@@ -0,0 +1,45 @@
+// check-pass
+
+#![feature(lint_reasons)]
+
+#![warn(unused)]
+
+// This expect attribute should catch all lint triggers
+#[expect(unused_variables)]
+fn check_multiple_lints_1() {
+    let value_i = 0xff00ff;
+    let value_ii = 0xff00ff;
+    let value_iii = 0xff00ff;
+    let value_iiii = 0xff00ff;
+    let value_iiiii = 0xff00ff;
+}
+
+// This expect attribute should catch all lint triggers
+#[expect(unused_mut)]
+fn check_multiple_lints_2() {
+    let mut a = 0xa;
+    let mut b = 0xb;
+    let mut c = 0xc;
+    println!("The ABC goes as: {:#x} {:#x} {:#x}", a, b, c);
+}
+
+// This expect attribute should catch all lint triggers
+#[expect(while_true)]
+fn check_multiple_lints_3() {
+    // `while_true` is an early lint
+    while true {}
+
+    while true {}
+
+    while true {}
+
+    while true {}
+
+    while true {}
+}
+
+fn main() {
+    check_multiple_lints_1();
+    check_multiple_lints_2();
+    check_multiple_lints_3();
+}

src/test/ui/lint/rfc-2383-lint-reason/crate_level_expect.rs

@@ -0,0 +1,15 @@
+// check-pass
+
+#![feature(lint_reasons)]
+
+#![warn(unused)]
+
+#![expect(unused_mut)]
+//~^ WARNING this lint expectation is unfulfilled [unfulfilled_lint_expectations]
+//~| NOTE `#[warn(unfulfilled_lint_expectations)]` on by default
+
+#![expect(unused_variables)]
+
+fn main() {
+    let x = 0;
+}

src/test/ui/lint/rfc-2383-lint-reason/crate_level_expect.stderr

@@ -0,0 +1,10 @@
+warning: this lint expectation is unfulfilled
+  --> $DIR/crate_level_expect.rs:7:1
+   |
+LL | #![expect(unused_mut)]
+   | ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(unfulfilled_lint_expectations)]` on by default
+
+warning: 1 warning emitted
+

src/test/ui/lint/rfc-2383-lint-reason/expect_inside_macro.rs

@@ -0,0 +1,16 @@
+// check-pass
+
+#![feature(lint_reasons)]
+
+#![warn(unused)]
+
+macro_rules! expect_inside_macro {
+    () => {
+        #[expect(unused_variables)]
+        let x = 0;
+    };
+}
+
+fn main() {
+    expect_inside_macro!();
+}

src/test/ui/lint/rfc-2383-lint-reason/expect_lint_from_macro.rs

@@ -0,0 +1,42 @@
+// check-pass
+
+#![feature(lint_reasons)]
+
+#![warn(unused_variables)]
+
+macro_rules! trigger_unused_variables_macro {
+    () => {
+        let x = 0;
+        //~^ WARNING unused variable: `x` [unused_variables]
+        //~| WARNING unused variable: `x` [unused_variables]
+    };
+}
+
+pub fn check_macro() {
+    // This should trigger the `unused_variables` from inside the macro
+    trigger_unused_variables_macro!();
+}
+
+// This should be fulfilled by the macro
+#[expect(unused_variables)]
+pub fn check_expect_on_item() {
+    trigger_unused_variables_macro!();
+}
+
+pub fn check_expect_on_macro() {
+    // This should be fulfilled by the macro
+    #[expect(unused_variables)]
+    trigger_unused_variables_macro!();
+
+    // FIXME: Lint attributes currently don't work directly on macros, and
+    // therefore also doesn't work for the new `expect` attribute. This bug
+    // is being tracked in rust#87391. The test will until then produce two
+    // warnings about the unused variable x.
+    //
+    // The expectation is still marked as fulfilled. I'm not totally why but
+    // my guess is that this will remain working when rust#87391 has been fixed.
+}
+
+fn main() {
+
+}

src/test/ui/lint/rfc-2383-lint-reason/expect_lint_from_macro.stderr

@@ -0,0 +1,29 @@
+warning: unused variable: `x`
+  --> $DIR/expect_lint_from_macro.rs:9:13
+   |
+LL |         let x = 0;
+   |             ^ help: if this is intentional, prefix it with an underscore: `_x`
+...
+LL |     trigger_unused_variables_macro!();
+   |     --------------------------------- in this macro invocation
+   |
+note: the lint level is defined here
+  --> $DIR/expect_lint_from_macro.rs:5:9
+   |
+LL | #![warn(unused_variables)]
+   |         ^^^^^^^^^^^^^^^^
+   = note: this warning originates in the macro `trigger_unused_variables_macro` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+warning: unused variable: `x`
+  --> $DIR/expect_lint_from_macro.rs:9:13
+   |
+LL |         let x = 0;
+   |             ^ help: if this is intentional, prefix it with an underscore: `_x`
+...
+LL |     trigger_unused_variables_macro!();
+   |     --------------------------------- in this macro invocation
+   |
+   = note: this warning originates in the macro `trigger_unused_variables_macro` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+warning: 2 warnings emitted
+

src/test/ui/lint/rfc-2383-lint-reason/expect_missing_feature_gate.rs

@@ -0,0 +1,9 @@
+// should error due to missing feature gate.
+
+#![warn(unused)]
+
+#[expect(unused)]
+//~^ ERROR: the `#[expect]` attribute is an experimental feature [E0658]
+fn main() {
+    let x = 1;
+}

src/test/ui/lint/rfc-2383-lint-reason/expect_missing_feature_gate.stderr

@@ -0,0 +1,12 @@
+error[E0658]: the `#[expect]` attribute is an experimental feature
+  --> $DIR/expect_missing_feature_gate.rs:5:1
+   |
+LL | #[expect(unused)]
+   | ^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #54503 <https://github.com/rust-lang/rust/issues/54503> for more information
+   = help: add `#![feature(lint_reasons)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.

src/test/ui/lint/rfc-2383-lint-reason/expect_multiple_lints.rs

@@ -0,0 +1,31 @@
+// check-pass
+
+#![feature(lint_reasons)]
+
+#![warn(unused)]
+
+#[expect(unused_variables, unused_mut, while_true)]
+fn check_multiple_lints_1() {
+    // This only trigger `unused_variables`
+    let who_am_i = 666;
+}
+
+#[expect(unused_variables, unused_mut, while_true)]
+fn check_multiple_lints_2() {
+    // This only triggers `unused_mut`
+    let mut x = 0;
+    println!("I use x: {}", x);
+}
+
+
+#[expect(unused_variables, unused_mut, while_true)]
+fn check_multiple_lints_3() {
+    // This only triggers `while_true` which is also an early lint
+    while true {}
+}
+
+fn main() {
+    check_multiple_lints_1();
+    check_multiple_lints_2();
+    check_multiple_lints_3();
+}