recover #[attr] if expr {}

src/librustc_parse/lib.rs

@@ -2,6 +2,7 @@
 
 #![feature(bool_to_option)]
 #![feature(crate_visibility_modifier)]
+#![feature(slice_patterns)]
 
 use syntax::ast;
 use syntax::print::pprust;

src/librustc_parse/parser/expr.rs

@@ -668,19 +668,20 @@ impl<'a> Parser<'a> {
             expr.map(|mut expr| {
                 attrs.extend::<Vec<_>>(expr.attrs.into());
                 expr.attrs = attrs;
-                match expr.kind {
-                    ExprKind::If(..) if !expr.attrs.is_empty() => {
-                        // Just point to the first attribute in there...
-                        let span = expr.attrs[0].span;
-                        self.span_err(span, "attributes are not yet allowed on `if` expressions");
-                    }
-                    _ => {}
-                }
+                self.error_attr_on_if_expr(&expr);
                 expr
             })
         )
     }
 
+    fn error_attr_on_if_expr(&self, expr: &Expr) {
+        if let (ExprKind::If(..), [a0, ..]) = (&expr.kind, &*expr.attrs) {
+            // Just point to the first attribute in there...
+            self.struct_span_err(a0.span, "attributes are not yet allowed on `if` expressions")
+                .emit();
+        }
+    }
+
     fn parse_dot_or_call_expr_with_(&mut self, e0: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
         let mut e = e0;
         let mut hi;

src/test/ui/parser/recovery-attr-on-if.rs

@@ -0,0 +1,9 @@
+fn main() {
+    #[attr] if true {};
+    //~^ ERROR cannot find attribute
+    //~| ERROR attributes are not yet allowed on `if` expressions
+    #[attr] if true {};
+    //~^ ERROR cannot find attribute
+    //~| ERROR attributes are not yet allowed on `if` expressions
+    let _recovery_witness: () = 0; //~ ERROR mismatched types
+}

src/test/ui/parser/recovery-attr-on-if.stderr

@@ -0,0 +1,35 @@
+error: attributes are not yet allowed on `if` expressions
+  --> $DIR/recovery-attr-on-if.rs:2:5
+   |
+LL |     #[attr] if true {};
+   |     ^^^^^^^
+
+error: attributes are not yet allowed on `if` expressions
+  --> $DIR/recovery-attr-on-if.rs:5:5
+   |
+LL |     #[attr] if true {};
+   |     ^^^^^^^
+
+error: cannot find attribute `attr` in this scope
+  --> $DIR/recovery-attr-on-if.rs:5:7
+   |
+LL |     #[attr] if true {};
+   |       ^^^^
+
+error: cannot find attribute `attr` in this scope
+  --> $DIR/recovery-attr-on-if.rs:2:7
+   |
+LL |     #[attr] if true {};
+   |       ^^^^
+
+error[E0308]: mismatched types
+  --> $DIR/recovery-attr-on-if.rs:8:33
+   |
+LL |     let _recovery_witness: () = 0;
+   |                            --   ^ expected `()`, found integer
+   |                            |
+   |                            expected due to this
+
+error: aborting due to 5 previous errors
+
+For more information about this error, try `rustc --explain E0308`.