Start sketching --depend support in rustc.

src/comp/driver/rustc.rs

@@ -142,6 +142,7 @@ options:
     --ls               list the symbols defined by a crate file
     -L <path>          add a directory to the library search path
     --noverify         suppress LLVM verification step (slight speedup)
+    --depend           print dependencies, in makefile-rule form
     --parse-only       parse only; do not compile, assemble, or link
     -O                 optimize
     -S                 compile only; do not assemble or link

src/comp/front/eval.rs

@@ -24,8 +24,15 @@ tag val {
     val_str(str);
 }
 
+tag eval_mode {
+    mode_depend;
+    mode_parse;
+}
+
 type env = vec[tup(ident, val)];
 type ctx = @rec(parser p,
+                eval_mode mode,
+                mutable vec[str] deps,
                 session.session sess,
                 mutable uint chpos);
 
@@ -383,6 +390,11 @@ fn eval_crate_directive(ctx cx,
 
             auto full_path = prefix + std.fs.path_sep() + file_path;
 
+            if (cx.mode == mode_depend) {
+                cx.deps += vec(full_path);
+                ret;
+            }
+
             auto start_id = cx.p.next_def_id();
             auto p0 = new_parser(cx.sess, e, start_id, full_path, cx.chpos);
             auto m0 = parse_mod_items(p0, token.EOF);

src/comp/front/parser.rs

@@ -2497,7 +2497,12 @@ fn parse_crate_from_crate_file(parser p) -> @ast.crate {
     auto lo = p.get_lo_pos();
     auto prefix = std.fs.dirname(p.get_filemap().name);
     auto cdirs = parse_crate_directives(p, token.EOF);
-    auto cx = @rec(p=p, sess=p.get_session(), mutable chpos=p.get_chpos());
+    let vec[str] deps = vec();
+    auto cx = @rec(p=p,
+                   mode=eval.mode_parse,
+                   mutable deps = deps,
+                   sess=p.get_session(),
+                   mutable chpos=p.get_chpos());
     auto m = eval.eval_crate_directives_to_mod(cx, p.get_env(),
                                                cdirs, prefix);
     auto hi = p.get_hi_pos();