Add branchy const in pattern tests

Author: ecstatic-morse

src/test/ui/consts/const_in_pattern/custom-eq-branch-pass.rs

@@ -0,0 +1,33 @@
+// run-pass
+
+#![feature(const_if_match)]
+#![warn(indirect_structural_match)]
+
+struct CustomEq;
+
+impl Eq for CustomEq {}
+impl PartialEq for CustomEq {
+    fn eq(&self, _: &Self) -> bool {
+        false
+    }
+}
+
+#[derive(PartialEq, Eq)]
+enum Foo {
+    Bar,
+    Baz,
+    Qux(CustomEq),
+}
+
+const BAR_BAZ: Foo = if 42 == 42 {
+    Foo::Bar
+} else {
+    Foo::Baz
+};
+
+fn main() {
+    match Foo::Qux(CustomEq) {
+        BAR_BAZ => panic!(),
+        _ => {}
+    }
+}

src/test/ui/consts/const_in_pattern/custom-eq-branch-warn.rs

@@ -0,0 +1,39 @@
+// check-pass
+
+#![feature(const_if_match)]
+#![warn(indirect_structural_match)]
+//~^ NOTE lint level is defined here
+
+struct CustomEq;
+
+impl Eq for CustomEq {}
+impl PartialEq for CustomEq {
+    fn eq(&self, _: &Self) -> bool {
+        false
+    }
+}
+
+#[derive(PartialEq, Eq)]
+enum Foo {
+    Bar,
+    Baz,
+    Qux(CustomEq),
+}
+
+// We know that `BAR_BAZ` will always be `Foo::Bar` and thus eligible for structural matching, but
+// dataflow will be more conservative.
+const BAR_BAZ: Foo = if 42 == 42 {
+    Foo::Bar
+} else {
+    Foo::Qux(CustomEq)
+};
+
+fn main() {
+    match Foo::Qux(CustomEq) {
+        BAR_BAZ => panic!(),
+        //~^ WARN must be annotated with `#[derive(PartialEq, Eq)]`
+        //~| WARN this was previously accepted
+        //~| NOTE see issue #62411
+        _ => {}
+    }
+}

src/test/ui/consts/const_in_pattern/custom-eq-branch-warn.stderr

@@ -0,0 +1,16 @@
+warning: to use a constant of type `CustomEq` in a pattern, `CustomEq` must be annotated with `#[derive(PartialEq, Eq)]`
+  --> $DIR/custom-eq-branch-warn.rs:33:9
+   |
+LL |         BAR_BAZ => panic!(),
+   |         ^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/custom-eq-branch-warn.rs:4:9
+   |
+LL | #![warn(indirect_structural_match)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #62411 <https://github.com/rust-lang/rust/issues/62411>
+
+warning: 1 warning emitted
+

src/test/ui/consts/const_in_pattern/no-eq-branch-fail.rs

@@ -0,0 +1,27 @@
+#![feature(const_if_match)]
+#![warn(indirect_structural_match)]
+
+struct NoEq;
+
+enum Foo {
+    Bar,
+    Baz,
+    Qux(NoEq),
+}
+
+// Even though any of these values can be compared structurally, we still disallow it in a pattern
+// because `Foo` does not impl `PartialEq`.
+const BAR_BAZ: Foo = if 42 == 42 {
+    Foo::Baz
+} else {
+    Foo::Bar
+};
+
+fn main() {
+    match Foo::Qux(NoEq) {
+        BAR_BAZ => panic!(),
+        //~^ ERROR must be annotated with `#[derive(PartialEq, Eq)]`
+        //~| ERROR must be annotated with `#[derive(PartialEq, Eq)]`
+        _ => {}
+    }
+}

src/test/ui/consts/const_in_pattern/no-eq-branch-fail.stderr

@@ -0,0 +1,14 @@
+error: to use a constant of type `Foo` in a pattern, `Foo` must be annotated with `#[derive(PartialEq, Eq)]`
+  --> $DIR/no-eq-branch-fail.rs:22:9
+   |
+LL |         BAR_BAZ => panic!(),
+   |         ^^^^^^^
+
+error: to use a constant of type `Foo` in a pattern, `Foo` must be annotated with `#[derive(PartialEq, Eq)]`
+  --> $DIR/no-eq-branch-fail.rs:22:9
+   |
+LL |         BAR_BAZ => panic!(),
+   |         ^^^^^^^
+
+error: aborting due to 2 previous errors
+