Make extern_absolute_paths only work on the new edition

Author: Manishearth

src/librustc_resolve/lib.rs

@@ -3277,9 +3277,8 @@ impl<'a> Resolver<'a> {
                     let prev_name = path[0].name;
                     if prev_name == keywords::Extern.name() ||
                        prev_name == keywords::CrateRoot.name() &&
-                       // Note: When this feature stabilizes, this should
-                       // be gated on sess.rust_2018()
-                       self.session.features_untracked().extern_absolute_paths {
+                       self.session.features_untracked().extern_absolute_paths &&
+                       self.session.rust_2018() {
                         // `::extern_crate::a::b`
                         let crate_id = self.crate_loader.process_path_extern(name, ident.span);
                         let crate_root =

src/librustc_resolve/resolve_imports.rs

@@ -646,7 +646,8 @@ impl<'a, 'b:'a> ImportResolver<'a, 'b> {
         if module_path.len() == 1 && (module_path[0].name == keywords::CrateRoot.name() ||
                                       module_path[0].name == keywords::Extern.name()) {
             let is_extern = module_path[0].name == keywords::Extern.name() ||
-                            self.session.features_untracked().extern_absolute_paths;
+                            (self.session.features_untracked().extern_absolute_paths &&
+                             self.session.rust_2018());
             match directive.subclass {
                 GlobImport { .. } if is_extern => {
                     return Some((directive.span,

src/libsyntax/feature_gate.rs

@@ -1849,8 +1849,10 @@ pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
     let mut feature_checker = FeatureChecker::default();
 
     for &(.., f_edition, set) in ACTIVE_FEATURES.iter() {
-        if f_edition <= crate_edition {
-            set(&mut features, DUMMY_SP);
+        if let Some(f_edition) = f_edition {
+            if f_edition <= crate_edition {
+                set(&mut features, DUMMY_SP);
+            }
         }
     }
 

src/test/compile-fail/rfc-2126-extern-absolute-paths/non-existent-1.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// compile-flags: --edition=2018 -Zunstable-options
+
 #![feature(extern_absolute_paths)]
 
 use xcrate::S; //~ ERROR can't find crate for `xcrate`

src/test/compile-fail/rfc-2126-extern-absolute-paths/non-existent-2.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// compile-flags: --edition=2018 -Zunstable-options
+
 #![feature(extern_absolute_paths)]
 
 fn main() {

src/test/compile-fail/rfc-2126-extern-absolute-paths/non-existent-3.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// compile-flags: --edition=2018 -Zunstable-options
+
 #![feature(extern_absolute_paths)]
 
 use ycrate; //~ ERROR can't find crate for `ycrate`

src/test/compile-fail/rfc-2126-extern-absolute-paths/single-segment.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 
 // aux-build:xcrate.rs
+// compile-flags: --edition=2018 -Zunstable-options
 
 #![feature(crate_in_paths)]
 #![feature(extern_absolute_paths)]

src/test/run-make-fulldeps/save-analysis-rfc2126/Makefile

@@ -1,9 +1,9 @@
 -include ../tools.mk
 
 all: extern_absolute_paths.rs extern_in_paths.rs krate2
-	$(RUSTC) extern_absolute_paths.rs -Zsave-analysis
+	$(RUSTC) extern_absolute_paths.rs -Zsave-analysis --edition=2018
 	cat $(TMPDIR)/save-analysis/extern_absolute_paths.json | "$(PYTHON)" validate_json.py
-	$(RUSTC) extern_in_paths.rs -Zsave-analysis
+	$(RUSTC) extern_in_paths.rs -Zsave-analysis --edition=2018
 	cat $(TMPDIR)/save-analysis/extern_in_paths.json | "$(PYTHON)" validate_json.py
 
 krate2: krate2.rs

src/test/run-pass/rfc-2126-extern-absolute-paths/basic.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 
 // aux-build:xcrate.rs
+// compile-flags: --edition=2018 -Zunstable-options
 
 #![feature(extern_absolute_paths)]
 

src/test/run-pass/rfc-2126-extern-absolute-paths/test.rs

@@ -12,7 +12,7 @@
 //
 // Regression test for #47075.
 
-// compile-flags: --test
+// compile-flags: --test --edition=2018 -Zunstable-options
 
 #![feature(extern_absolute_paths)]