add tests for refutable patterns

Author: b-naber

tests/ui/pattern/issue-76342.rs

@@ -2,15 +2,21 @@
 #![allow(unused_variables)]
 struct Zeroes;
 impl Into<[usize; 2]> for Zeroes {
-    fn into(self) -> [usize; 2] { [0; 2] }
+    fn into(self) -> [usize; 2] {
+        [0; 2]
+    }
 }
 impl Into<[usize; 3]> for Zeroes {
-    fn into(self) -> [usize; 3] { [0; 3] }
+    fn into(self) -> [usize; 3] {
+        [0; 3]
+    }
 }
 impl Into<[usize; 4]> for Zeroes {
-    fn into(self) -> [usize; 4] { [0; 4] }
+    fn into(self) -> [usize; 4] {
+        [0; 4]
+    }
 }
 fn main() {
-    let [a, b, c] = Zeroes.into(); // ERROR: type annotations needed
-    let [d, e, f]: [_; 3] = Zeroes.into(); // Works great
+    let [a, b, c] = Zeroes.into();
+    let [d, e, f]: [_; 3] = Zeroes.into();
 }

tests/ui/pattern/slice-pattern-refutable.rs

@@ -0,0 +1,34 @@
+#![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() {}

tests/ui/pattern/slice-pattern-refutable.stderr

@@ -0,0 +1,40 @@
+error[E0282]: type annotations needed
+  --> $DIR/slice-pattern-refutable.rs:12:9
+   |
+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:19:31
+   |
+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:26:31
+   |
+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`.

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() {}

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`.