add a series of tests for changes to structs

These tests reveal that the edges are in some cases
too strict.

src/test/incremental/struct_remove_field.rs

@@ -0,0 +1,52 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Test incremental compilation tracking where we change field names
+// in between revisions (hashing should be stable).
+
+// revisions:rpass1 rpass2
+
+#![feature(rustc_attrs)]
+
+#[cfg(rpass1)]
+pub struct X {
+    pub x: u32,
+    pub x2: u32,
+}
+
+#[cfg(rpass2)]
+pub struct X {
+    pub x: u32,
+}
+
+pub struct EmbedX {
+    x: X
+}
+
+pub struct Y {
+    pub y: char
+}
+
+#[rustc_dirty(label="TypeckItemBody", cfg="rpass2")]
+pub fn use_X(x: X) -> u32 {
+    x.x as u32
+}
+
+#[rustc_dirty(label="TypeckItemBody", cfg="rpass2")]
+pub fn use_EmbedX(embed: EmbedX) -> u32 {
+    embed.x.x as u32
+}
+
+#[rustc_dirty(label="TypeckItemBody", cfg="rpass2")] // FIXME(#33850) should be clean
+pub fn use_Y() {
+    let x: Y = Y { y: 'c' };
+}
+
+pub fn main() { }