Add a test for invalid syntax in attribute

Author: meithecatte

test_suite/ui/invalid_attribute_syntax.rs

@@ -0,0 +1,33 @@
+use enumflags2::bitflags;
+
+#[bitflags(default = A + B)]
+enum Test {
+    A = 1,
+    B = 2,
+}
+
+#[bitflags(default = A |)]
+enum Test {
+    A = 1,
+    B = 2,
+}
+
+#[bitflags(default =)]
+enum Test {
+    A = 1,
+    B = 2,
+}
+
+#[bitflags(default)]
+enum Test {
+    A = 1,
+    B = 2,
+}
+
+#[bitflags(yes)]
+enum Test {
+    A = 1,
+    B = 2,
+}
+
+fn main() {}

test_suite/ui/invalid_attribute_syntax.stderr

@@ -0,0 +1,35 @@
+error: expected `|`
+ --> $DIR/invalid_attribute_syntax.rs:3:24
+  |
+3 | #[bitflags(default = A + B)]
+  |                        ^
+
+error: unexpected end of input, expected identifier
+ --> $DIR/invalid_attribute_syntax.rs:9:1
+  |
+9 | #[bitflags(default = A |)]
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^^
+  |
+  = note: this error originates in an attribute macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: unexpected end of input, expected identifier
+  --> $DIR/invalid_attribute_syntax.rs:15:1
+   |
+15 | #[bitflags(default =)]
+   | ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this error originates in an attribute macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: expected `=`
+  --> $DIR/invalid_attribute_syntax.rs:21:1
+   |
+21 | #[bitflags(default)]
+   | ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this error originates in an attribute macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: expected `default`
+  --> $DIR/invalid_attribute_syntax.rs:27:12
+   |
+27 | #[bitflags(yes)]
+   |            ^^^