Add stability attribute eager expansion test

    error: expected unsuffixed literal or identifier, found `stable_feature`
      --> tests/ui/stability-attribute/eager-expansion.rs:37:32
       |
    LL |               #[stable(feature = stable_feature!($signedness), since = stable_since!($signedness))]
       |                                  ^^^^^^^^^^^^^^
    ...
    LL | / nonzero_integers! {
    LL | |     unsigned NonZeroU8(u8)
    LL | |     unsigned NonZeroU16(u16)
    LL | |     unsigned NonZeroU32(u32)
    ...  |
    LL | |     signed NonZeroI64(u64)
    LL | | }
       | |_- in this macro invocation
       |
       = note: this error originates in the macro `nonzero_integers` (in Nightly builds, run with -Z macro-backtrace for more info)

Author: dtolnay

tests/ui/stability-attribute/eager-expansion.rs

@@ -0,0 +1,54 @@
+// check-pass
+
+#![crate_type = "lib"]
+#![feature(staged_api)]
+#![stable(feature = "stable_test_feature", since = "3.3.3")]
+
+macro_rules! sign_dependent_expr {
+    (unsigned ? if unsigned { $unsigned_case:expr } if signed { $signed_case:expr }) => {
+        $unsigned_case
+    };
+    (signed ? if unsigned { $unsigned_case:expr } if signed { $signed_case:expr }) => {
+        $signed_case
+    };
+}
+
+macro_rules! stable_feature {
+    ($signedness:ident) => {
+        sign_dependent_expr! {
+            $signedness ?
+            if unsigned { "nonzero" }
+            if signed { "signed_nonzero" }
+        }
+    };
+}
+
+macro_rules! stable_since {
+    ($signedness:ident) => {
+        sign_dependent_expr! {
+            $signedness ?
+            if unsigned { "1.28.0" }
+            if signed { "1.34.0" }
+        }
+    };
+}
+
+macro_rules! nonzero_integers {
+    ($($signedness:ident $NonZero:ident($primitive:ty))*) => {
+        $(
+            #[stable(feature = stable_feature!($signedness), since = stable_since!($signedness))]
+            pub struct $NonZero($primitive);
+        )*
+    };
+}
+
+nonzero_integers! {
+    unsigned NonZeroU8(u8)
+    unsigned NonZeroU16(u16)
+    unsigned NonZeroU32(u32)
+    unsigned NonZeroU64(u64)
+    signed NonZeroI8(i8)
+    signed NonZeroI16(i16)
+    signed NonZeroI32(i32)
+    signed NonZeroI64(i64)
+}