8 files changed, 293 insertions, 0 deletions
diff --git a/tests/ui/pattern/slice-array-infer.rs b/tests/ui/pattern/slice-array-infer.rs
new file mode 100644
index 000000000..f94a3dcfe
--- /dev/null
+++ b/tests/ui/pattern/slice-array-infer.rs
@@ -0,0 +1,27 @@
+// check-pass
+
+#![allow(unused_variables)]
+#![feature(generic_arg_infer)]
+
+struct Zeroes;
+impl Into<&'static [usize; 3]> for Zeroes {
+    fn into(self) -> &'static [usize; 3] {
+        &[0; 3]
+    }
+}
+impl Into<[usize; 3]> for Zeroes {
+    fn into(self) -> [usize; 3] {
+        [0; 3]
+    }
+}
+fn main() {
+    let [a, b, c] = Zeroes.into();
+    let [d, e, f] = <Zeroes as Into<&'static [usize; 3]>>::into(Zeroes);
+    let &[g, h, i] = Zeroes.into();
+    let [j, k, l]: [usize; _] = Zeroes.into();
+    let [m, n, o]: &[usize; _] = Zeroes.into();
+
+    // check the binding mode of these patterns:
+    let _: &[usize] = &[a, b, c, g, h, i, j, k, l];
+    let _: &[&usize] = &[d, e, f, m, n, o];
+}
diff --git a/tests/ui/pattern/slice-pattern-refutable.rs b/tests/ui/pattern/slice-pattern-refutable.rs
new file mode 100644
index 000000000..1be3c6ef8
--- /dev/null
+++ b/tests/ui/pattern/slice-pattern-refutable.rs
@@ -0,0 +1,36 @@
+// Test that we do not infer the expected types of patterns to an array
+// if we're in a refutable pattern.
+#![allow(unused_variables)]
+
+struct Zeroes;
+
+impl Into<[usize; 3]> for Zeroes {
+    fn into(self) -> [usize; 3] {
+        [0; 3]
+    }
+}
+
+fn let_else() {
+    let [a, b, c] = Zeroes.into() else {
+        //~^ ERROR type annotations needed
+        unreachable!();
+    };
+}
+
+fn if_let() {
+    if let [a, b, c] = Zeroes.into() {
+        //~^ ERROR type annotations needed
+        unreachable!();
+    }
+}
+
+fn if_let_else() {
+    if let [a, b, c] = Zeroes.into() {
+        //~^ ERROR type annotations needed
+        unreachable!();
+    } else {
+        unreachable!();
+    }
+}
+
+fn main() {}
diff --git a/tests/ui/pattern/slice-pattern-refutable.stderr b/tests/ui/pattern/slice-pattern-refutable.stderr
new file mode 100644
index 000000000..df5b58d3e
--- /dev/null
+++ b/tests/ui/pattern/slice-pattern-refutable.stderr
@@ -0,0 +1,40 @@
+error[E0282]: type annotations needed
+  --> $DIR/slice-pattern-refutable.rs:14:9
+   |
+LL |     let [a, b, c] = Zeroes.into() else {
+   |         ^^^^^^^^^
+   |
+help: consider giving this pattern a type
+   |
+LL |     let [a, b, c]: /* Type */ = Zeroes.into() else {
+   |                  ++++++++++++
+
+error[E0282]: type annotations needed
+  --> $DIR/slice-pattern-refutable.rs:21:31
+   |
+LL |     if let [a, b, c] = Zeroes.into() {
+   |            ---------          ^^^^
+   |            |
+   |            type must be known at this point
+   |
+help: try using a fully qualified path to specify the expected types
+   |
+LL |     if let [a, b, c] = <Zeroes as Into<T>>::into(Zeroes) {
+   |                        ++++++++++++++++++++++++++      ~
+
+error[E0282]: type annotations needed
+  --> $DIR/slice-pattern-refutable.rs:28:31
+   |
+LL |     if let [a, b, c] = Zeroes.into() {
+   |            ---------          ^^^^
+   |            |
+   |            type must be known at this point
+   |
+help: try using a fully qualified path to specify the expected types
+   |
+LL |     if let [a, b, c] = <Zeroes as Into<T>>::into(Zeroes) {
+   |                        ++++++++++++++++++++++++++      ~
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0282`.
diff --git a/tests/ui/pattern/slice-patterns-ambiguity.rs b/tests/ui/pattern/slice-patterns-ambiguity.rs
new file mode 100644
index 000000000..0fe24b0e5
--- /dev/null
+++ b/tests/ui/pattern/slice-patterns-ambiguity.rs
@@ -0,0 +1,47 @@
+#![allow(unused_variables)]
+
+struct Zeroes;
+
+const ARR: [usize; 2] = [0; 2];
+const ARR2: [usize; 2] = [2; 2];
+
+impl Into<&'static [usize; 2]> for Zeroes {
+    fn into(self) -> &'static [usize; 2] {
+        &ARR
+    }
+}
+
+impl Into<&'static [usize]> for Zeroes {
+    fn into(self) -> &'static [usize] {
+        &ARR2
+    }
+}
+
+fn let_decl() {
+    let &[a, b] = Zeroes.into();
+}
+
+fn let_else() {
+    let &[a, b] = Zeroes.into() else {
+        //~^ ERROR type annotations needed
+        unreachable!();
+    };
+}
+
+fn if_let() {
+    if let &[a, b] = Zeroes.into() {
+        //~^ ERROR type annotations needed
+        unreachable!();
+    }
+}
+
+fn if_let_else() {
+    if let &[a, b] = Zeroes.into() {
+        //~^ ERROR type annotations needed
+        unreachable!();
+    } else {
+        unreachable!();
+    }
+}
+
+fn main() {}
diff --git a/tests/ui/pattern/slice-patterns-ambiguity.stderr b/tests/ui/pattern/slice-patterns-ambiguity.stderr
new file mode 100644
index 000000000..3ef99d0e2
--- /dev/null
+++ b/tests/ui/pattern/slice-patterns-ambiguity.stderr
@@ -0,0 +1,40 @@
+error[E0282]: type annotations needed for `&_`
+  --> $DIR/slice-patterns-ambiguity.rs:25:9
+   |
+LL |     let &[a, b] = Zeroes.into() else {
+   |         ^^^^^^^
+   |
+help: consider giving this pattern a type, where the placeholders `_` are specified
+   |
+LL |     let &[a, b]: &_ = Zeroes.into() else {
+   |                ++++
+
+error[E0282]: type annotations needed
+  --> $DIR/slice-patterns-ambiguity.rs:32:29
+   |
+LL |     if let &[a, b] = Zeroes.into() {
+   |             ------          ^^^^
+   |             |
+   |             type must be known at this point
+   |
+help: try using a fully qualified path to specify the expected types
+   |
+LL |     if let &[a, b] = <Zeroes as Into<&_>>::into(Zeroes) {
+   |                      +++++++++++++++++++++++++++      ~
+
+error[E0282]: type annotations needed
+  --> $DIR/slice-patterns-ambiguity.rs:39:29
+   |
+LL |     if let &[a, b] = Zeroes.into() {
+   |             ------          ^^^^
+   |             |
+   |             type must be known at this point
+   |
+help: try using a fully qualified path to specify the expected types
+   |
+LL |     if let &[a, b] = <Zeroes as Into<&_>>::into(Zeroes) {
+   |                      +++++++++++++++++++++++++++      ~
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0282`.
diff --git a/tests/ui/pattern/slice-patterns-irrefutable.rs b/tests/ui/pattern/slice-patterns-irrefutable.rs
new file mode 100644
index 000000000..bd230608e
--- /dev/null
+++ b/tests/ui/pattern/slice-patterns-irrefutable.rs
@@ -0,0 +1,74 @@
+// Test that we infer the expected type of a pattern to an array of the given length.
+
+#![allow(unused_variables)]
+
+use std::array::TryFromSliceError;
+use std::convert::TryInto;
+
+struct Zeroes;
+impl Into<[usize; 2]> for Zeroes {
+    fn into(self) -> [usize; 2] {
+        [0; 2]
+    }
+}
+impl Into<[usize; 3]> for Zeroes {
+    fn into(self) -> [usize; 3] {
+        [0; 3]
+    }
+}
+impl Into<[usize; 4]> for Zeroes {
+    fn into(self) -> [usize; 4] {
+        [0; 4]
+    }
+}
+
+fn zeroes_into() {
+    let [a, b, c] = Zeroes.into();
+    let [d, e, f]: [_; 3] = Zeroes.into();
+}
+
+fn array_try_from(x: &[usize]) -> Result<usize, TryFromSliceError> {
+    let [a, b] = x.try_into()?;
+    Ok(a + b)
+}
+
+fn destructuring_assignment() {
+    let a: i32;
+    let b;
+    [a, b] = Default::default();
+}
+
+fn test_nested_array() {
+    let a: [_; 3];
+    let b;
+    //~^ ERROR type annotations needed
+    [a, b] = Default::default();
+}
+
+fn test_nested_array_type_hint() {
+    let a: [_; 3];
+    let b;
+    [a, b] = Default::default();
+    let _: i32 = b[1];
+}
+
+fn test_working_nested_array() {
+    let a: i32;
+    [[a, _, _], _, _] = Default::default();
+}
+
+struct Foo<T>([T; 2]);
+
+impl<T: Default + Copy> Default for Foo<T> {
+    fn default() -> Self {
+        Foo([Default::default(); 2])
+    }
+}
+
+fn field_array() {
+    let a: i32;
+    let b;
+    Foo([a, b]) = Default::default();
+}
+
+fn main() {}
diff --git a/tests/ui/pattern/slice-patterns-irrefutable.stderr b/tests/ui/pattern/slice-patterns-irrefutable.stderr
new file mode 100644
index 000000000..fac99534f
--- /dev/null
+++ b/tests/ui/pattern/slice-patterns-irrefutable.stderr
@@ -0,0 +1,14 @@
+error[E0282]: type annotations needed for `[_; 3]`
+  --> $DIR/slice-patterns-irrefutable.rs:43:9
+   |
+LL |     let b;
+   |         ^
+   |
+help: consider giving `b` an explicit type, where the placeholders `_` are specified
+   |
+LL |     let b: [_; 3];
+   |          ++++++++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0282`.
diff --git a/tests/ui/pattern/slice-patterns-nested.rs b/tests/ui/pattern/slice-patterns-nested.rs
new file mode 100644
index 000000000..077e0a139
--- /dev/null
+++ b/tests/ui/pattern/slice-patterns-nested.rs
@@ -0,0 +1,15 @@
+// check-pass
+#![allow(unused_variables)]
+
+struct Zeroes;
+struct Foo<T>(T);
+
+impl Into<[usize; 3]> for Zeroes {
+    fn into(self) -> [usize; 3] {
+        [0; 3]
+    }
+}
+
+fn main() {
+    let Foo([a, b, c]) = Foo(Zeroes.into());
+}