auto merge of #17506 : sfackler/rust/cfg-attr, r=alexcrichton

cc #17490 

Reopening of #16230

2 files changed, 59 insertions, 0 deletions

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index b35a9456757..8bf13e20fed 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -439,6 +439,8 @@ fn initial_syntax_expander_table() -> SyntaxEnv {
     syntax_expanders.insert(intern("cfg"),
                             builtin_normal_expander(
                                     ext::cfg::expand_cfg));
+    syntax_expanders.insert(intern("cfg_attr"),
+                            Modifier(box ext::cfg_attr::expand));
     syntax_expanders.insert(intern("trace_macros"),
                             builtin_normal_expander(
                                     ext::trace_macros::expand_trace_macros));
diff --git a/src/libsyntax/ext/cfg_attr.rs b/src/libsyntax/ext/cfg_attr.rs
new file mode 100644
index 00000000000..ad02b50f248
--- /dev/null
+++ b/src/libsyntax/ext/cfg_attr.rs
@@ -0,0 +1,57 @@
+// 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.
+
+use ast;
+use attr;
+use codemap::Span;
+use ext::base::ExtCtxt;
+use ext::build::AstBuilder;
+use ptr::P;
+
+pub fn expand(cx: &mut ExtCtxt, sp: Span, mi: &ast::MetaItem, it: P<ast::Item>) -> P<ast::Item> {
+    let (cfg, attr) = match mi.node {
+        ast::MetaList(_, ref mis) if mis.len() == 2 => (&mis[0], &mis[1]),
+        _ => {
+            cx.span_err(sp, "expected `#[cfg_attr(<cfg pattern>, <attr>)]`");
+            return it;
+        }
+    };
+
+    let mut out = (*it).clone();
+    if cfg_matches(cx, &**cfg) {
+        out.attrs.push(cx.attribute(attr.span, attr.clone()));
+    }
+
+    P(out)
+}
+
+fn cfg_matches(cx: &mut ExtCtxt, cfg: &ast::MetaItem) -> bool {
+    match cfg.node {
+        ast::MetaList(ref pred, ref mis) if pred.get() == "any" =>
+            mis.iter().any(|mi| cfg_matches(cx, &**mi)),
+        ast::MetaList(ref pred, ref mis) if pred.get() == "all" =>
+            mis.iter().all(|mi| cfg_matches(cx, &**mi)),
+        ast::MetaList(ref pred, ref mis) if pred.get() == "not" => {
+            if mis.len() != 1 {
+                cx.span_err(cfg.span, format!("expected 1 value, got {}",
+                                              mis.len()).as_slice());
+                return false;
+            }
+            !cfg_matches(cx, &*mis[0])
+        }
+        ast::MetaList(ref pred, _) => {
+            cx.span_err(cfg.span,
+                        format!("invalid predicate `{}`", pred).as_slice());
+            false
+        },
+        ast::MetaWord(_) | ast::MetaNameValue(..) =>
+            attr::contains(cx.cfg.as_slice(), cfg),
+    }
+}