FIXME: tests for avoiding changes inside expansions

Author: dianne

tests/ui/pattern/rfc-3627-match-ergonomics-2024/auxiliary/migration_lint_macros.rs

@@ -16,3 +16,10 @@ macro_rules! bind_ref {
         ref $foo
     };
 }
+
+#[macro_export]
+macro_rules! match_ref {
+    ($p:pat) => {
+        &$p
+    };
+}

tests/ui/pattern/rfc-3627-match-ergonomics-2024/migration_lint.fixed

@@ -243,9 +243,19 @@ fn main() {
     //~^ ERROR: binding modifiers may only be written when the default binding mode is `move`
     assert_type_eq(a, &0u32);
 
+    let &[migration_lint_macros::match_ref!(a)] = &[&0];
+    //~^ ERROR: reference patterns may only be written when the default binding mode is `move`
+    assert_type_eq(a, 0u32);
+
     // Test that we use the correct span when labeling a `&` whose subpattern is from an expansion.
+    // Also test that we don't simplify `&ref x` to `x` when the `ref` is from an expansion.
     let &[&migration_lint_macros::bind_ref!(a)] = &[&0];
     //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(a, &0u32);
+
+    // Test that we don't simplify `&ref x` to `x` when the `&` is from an expansion.
+    let &[migration_lint_macros::match_ref!(ref a)] = &[&0];
+    //~^ ERROR: reference patterns may only be written when the default binding mode is `move`
+    assert_type_eq(a, &0u32);
 }

tests/ui/pattern/rfc-3627-match-ergonomics-2024/migration_lint.rs

@@ -243,9 +243,19 @@ fn main() {
     //~^ ERROR: binding modifiers may only be written when the default binding mode is `move`
     assert_type_eq(a, &0u32);
 
+    let [migration_lint_macros::match_ref!(a)] = &[&0];
+    //~^ ERROR: reference patterns may only be written when the default binding mode is `move`
+    assert_type_eq(a, 0u32);
+
     // Test that we use the correct span when labeling a `&` whose subpattern is from an expansion.
+    // Also test that we don't simplify `&ref x` to `x` when the `ref` is from an expansion.
     let [&migration_lint_macros::bind_ref!(a)] = &[&0];
     //~^ ERROR: reference patterns may only be written when the default binding mode is `move` in Rust 2024
     //~| WARN: this changes meaning in Rust 2024
     assert_type_eq(a, &0u32);
+
+    // Test that we don't simplify `&ref x` to `x` when the `&` is from an expansion.
+    let [migration_lint_macros::match_ref!(ref a)] = &[&0];
+    //~^ ERROR: reference patterns may only be written when the default binding mode is `move`
+    assert_type_eq(a, &0u32);
 }

tests/ui/pattern/rfc-3627-match-ergonomics-2024/migration_lint.stderr

@@ -585,16 +585,34 @@ help: make the implied reference pattern explicit
 LL |     let &[migration_lint_macros::bind_ref!(a)] = &[0];
    |         +
 
+error: reference patterns may only be written when the default binding mode is `move`
+  --> $DIR/migration_lint.rs:246:10
+   |
+LL |     let [migration_lint_macros::match_ref!(a)] = &[&0];
+   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ occurs within macro expansion
+   |
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: matching on a reference type with a non-reference pattern changes the default binding mode
+  --> $DIR/migration_lint.rs:246:9
+   |
+LL |     let [migration_lint_macros::match_ref!(a)] = &[&0];
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this matches on type `&_`
+   = note: this error originates in the macro `migration_lint_macros::match_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: make the implied reference pattern explicit
+   |
+LL |     let &[migration_lint_macros::match_ref!(a)] = &[&0];
+   |         +
+
 error: reference patterns may only be written when the default binding mode is `move` in Rust 2024
-  --> $DIR/migration_lint.rs:249:10
+  --> $DIR/migration_lint.rs:252:10
    |
 LL |     let [&migration_lint_macros::bind_ref!(a)] = &[&0];
    |          ^ reference pattern not allowed under `ref` default binding mode
    |
    = warning: this changes meaning in Rust 2024
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
 note: matching on a reference type with a non-reference pattern changes the default binding mode
-  --> $DIR/migration_lint.rs:249:9
+  --> $DIR/migration_lint.rs:252:9
    |
 LL |     let [&migration_lint_macros::bind_ref!(a)] = &[&0];
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this matches on type `&_`
@@ -603,5 +621,23 @@ help: make the implied reference pattern explicit
 LL |     let &[&migration_lint_macros::bind_ref!(a)] = &[&0];
    |         +
 
-error: aborting due to 31 previous errors
+error: reference patterns may only be written when the default binding mode is `move`
+  --> $DIR/migration_lint.rs:258:10
+   |
+LL |     let [migration_lint_macros::match_ref!(ref a)] = &[&0];
+   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ occurs within macro expansion
+   |
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/match-ergonomics.html>
+note: matching on a reference type with a non-reference pattern changes the default binding mode
+  --> $DIR/migration_lint.rs:258:9
+   |
+LL |     let [migration_lint_macros::match_ref!(ref a)] = &[&0];
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this matches on type `&_`
+   = note: this error originates in the macro `migration_lint_macros::match_ref` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: make the implied reference pattern explicit
+   |
+LL |     let &[migration_lint_macros::match_ref!(ref a)] = &[&0];
+   |         +
+
+error: aborting due to 33 previous errors