rustc: Support stability attributes on crates

This commit adds support for linting `extern crate` statements for stability
attributes attached to the crate itself. This is likely to be the mechanism used
to deny access to experimental crates that are part of the standard
distribution.

cc #18585

Author: alexcrichton

src/librustc/lint/builtin.rs

@@ -45,7 +45,7 @@ use syntax::ast_map;
 use syntax::ast_util::is_shift_binop;
 use syntax::attr::AttrMetaMethods;
 use syntax::attr;
-use syntax::codemap::Span;
+use syntax::codemap::{Span, DUMMY_SP};
 use syntax::parse::token;
 use syntax::{ast, ast_util, visit};
 use syntax::ast::{TyI, TyU, TyI8, TyU8, TyI16, TyU16, TyI32, TyU32, TyI64, TyU64};
@@ -1553,11 +1553,57 @@ declare_lint!(UNSTABLE, Allow,
 /// `#[unstable]` attributes, or no stability attribute.
 pub struct Stability;
 
+impl Stability {
+    fn lint(&self, cx: &Context, id: ast::DefId, span: Span) {
+        let stability = stability::lookup(cx.tcx, id);
+        let cross_crate = !ast_util::is_local(id);
+
+        // stability attributes are promises made across crates; only
+        // check DEPRECATED for crate-local usage.
+        let (lint, label) = match stability {
+            // no stability attributes == Unstable
+            None if cross_crate => (UNSTABLE, "unmarked"),
+            Some(attr::Stability { level: attr::Unstable, .. }) if cross_crate =>
+                (UNSTABLE, "unstable"),
+            Some(attr::Stability { level: attr::Experimental, .. }) if cross_crate =>
+                (EXPERIMENTAL, "experimental"),
+            Some(attr::Stability { level: attr::Deprecated, .. }) =>
+                (DEPRECATED, "deprecated"),
+            _ => return
+        };
+
+        let msg = match stability {
+            Some(attr::Stability { text: Some(ref s), .. }) => {
+                format!("use of {} item: {}", label, *s)
+            }
+            _ => format!("use of {} item", label)
+        };
+
+        cx.span_lint(lint, span, msg.as_slice());
+    }
+}
+
 impl LintPass for Stability {
     fn get_lints(&self) -> LintArray {
         lint_array!(DEPRECATED, EXPERIMENTAL, UNSTABLE)
     }
 
+    fn check_view_item(&mut self, cx: &Context, item: &ast::ViewItem) {
+        // compiler-generated `extern crate` statements have a dummy span.
+        if item.span == DUMMY_SP { return }
+
+        let id = match item.node {
+            ast::ViewItemExternCrate(_, _, id) => id,
+            ast::ViewItemUse(..) => return,
+        };
+        let cnum = match cx.tcx.sess.cstore.find_extern_mod_stmt_cnum(id) {
+            Some(cnum) => cnum,
+            None => return,
+        };
+        let id = ast::DefId { krate: cnum, node: ast::CRATE_NODE_ID };
+        self.lint(cx, id, item.span);
+    }
+
     fn check_expr(&mut self, cx: &Context, e: &ast::Expr) {
         // first, check if the given expression was generated by a macro or not
         // we need to go back the expn_info tree to check only the arguments
@@ -1629,32 +1675,7 @@ impl LintPass for Stability {
             }
             _ => return
         };
-
-        let stability = stability::lookup(cx.tcx, id);
-        let cross_crate = !ast_util::is_local(id);
-
-        // stability attributes are promises made across crates; only
-        // check DEPRECATED for crate-local usage.
-        let (lint, label) = match stability {
-            // no stability attributes == Unstable
-            None if cross_crate => (UNSTABLE, "unmarked"),
-            Some(attr::Stability { level: attr::Unstable, .. }) if cross_crate =>
-                (UNSTABLE, "unstable"),
-            Some(attr::Stability { level: attr::Experimental, .. }) if cross_crate =>
-                (EXPERIMENTAL, "experimental"),
-            Some(attr::Stability { level: attr::Deprecated, .. }) =>
-                (DEPRECATED, "deprecated"),
-            _ => return
-        };
-
-        let msg = match stability {
-            Some(attr::Stability { text: Some(ref s), .. }) => {
-                format!("use of {} item: {}", label, *s)
-            }
-            _ => format!("use of {} item", label)
-        };
-
-        cx.span_lint(lint, span, msg.as_slice());
+        self.lint(cx, id, span);
     }
 }
 

src/test/compile-fail/lint-output-format.rs

@@ -11,7 +11,7 @@
 // compile-flags:-F experimental -D unstable
 // aux-build:lint_output_format.rs
 
-extern crate lint_output_format;
+extern crate lint_output_format; //~ ERROR: use of unmarked item
 use lint_output_format::{foo, bar, baz};
 
 fn main() {

src/test/compile-fail/lint-stability.rs

@@ -19,7 +19,7 @@
 
 mod cross_crate {
     #[phase(plugin, link)]
-    extern crate lint_stability;
+    extern crate lint_stability; //~ ERROR: use of unmarked item
     use self::lint_stability::*;
 
     fn test() {
@@ -144,7 +144,7 @@ mod cross_crate {
 }
 
 mod inheritance {
-    extern crate inherited_stability;
+    extern crate inherited_stability; //~ ERROR: use of experimental item
     use self::inherited_stability::*;
 
     fn test_inheritance() {