1 files changed, 47 insertions, 0 deletions
diff --git a/src/test/ui/associated-consts/defaults-not-assumed-fail.rs b/src/test/ui/associated-consts/defaults-not-assumed-fail.rs
new file mode 100644
index 000000000..3936e6a3b
--- /dev/null
+++ b/src/test/ui/associated-consts/defaults-not-assumed-fail.rs
@@ -0,0 +1,47 @@
+// build-fail
+
+trait Tr {
+    const A: u8 = 255;
+
+    // This should not be a constant evaluation error (overflow). The value of
+    // `Self::A` must not be assumed to hold inside the trait.
+    const B: u8 = Self::A + 1;
+    //~^ ERROR any use of this value will cause an error
+    //~| WARN this was previously accepted by the compiler but is being phased out
+}
+
+// An impl that doesn't override any constant will NOT cause a const eval error
+// just because it's defined, but only if the bad constant is used anywhere.
+// This matches the behavior without defaults.
+impl Tr for () {}
+
+// An impl that overrides either constant with a suitable value will be fine.
+impl Tr for u8 {
+    const A: u8 = 254;
+}
+
+impl Tr for u16 {
+    const B: u8 = 0;
+}
+
+impl Tr for u32 {
+    const A: u8 = 254;
+    const B: u8 = 0;
+}
+
+fn main() {
+    assert_eq!(<() as Tr>::A, 255);
+    assert_eq!(<() as Tr>::B, 0);    // causes the error above
+    //~^ ERROR evaluation of constant value failed
+    //~| ERROR erroneous constant used
+    //~| WARN this was previously accepted by the compiler but is being phased out
+
+    assert_eq!(<u8 as Tr>::A, 254);
+    assert_eq!(<u8 as Tr>::B, 255);
+
+    assert_eq!(<u16 as Tr>::A, 255);
+    assert_eq!(<u16 as Tr>::B, 0);
+
+    assert_eq!(<u32 as Tr>::A, 254);
+    assert_eq!(<u32 as Tr>::B, 0);
+}