resolve: Consistently use old decls before new decls in interfaces

The opposite ordering was a consistent source of confusion during debuggingю
`report_conflict` actually used an incorrect order due to similar confusion.

Author: petrochenkov

compiler/rustc_resolve/src/diagnostics.rs

@@ -212,12 +212,12 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         &mut self,
         ident: Ident,
         ns: Namespace,
-        new_binding: Decl<'ra>,
         old_binding: Decl<'ra>,
+        new_binding: Decl<'ra>,
     ) {
         // Error on the second of two conflicting names
         if old_binding.span.lo() > new_binding.span.lo() {
-            return self.report_conflict(ident, ns, old_binding, new_binding);
+            return self.report_conflict(ident, ns, new_binding, old_binding);
         }
 
         let container = match old_binding.parent_module.unwrap().kind {

compiler/rustc_resolve/src/imports.rs

@@ -348,8 +348,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     /// decide which one to keep.
     fn select_glob_decl(
         &self,
-        glob_decl: Decl<'ra>,
         old_glob_decl: Decl<'ra>,
+        glob_decl: Decl<'ra>,
         warn_ambiguity: bool,
     ) -> Decl<'ra> {
         assert!(glob_decl.is_glob_import());
@@ -369,7 +369,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         // with the re-fetched decls.
         // This is probably incorrect in corner cases, and the outdated decls still get
         // propagated to other places and get stuck there, but that's what we have at the moment.
-        let (deep_decl, old_deep_decl) = remove_same_import(glob_decl, old_glob_decl);
+        let (old_deep_decl, deep_decl) = remove_same_import(old_glob_decl, glob_decl);
         if deep_decl != glob_decl {
             // Some import layers have been removed, need to overwrite.
             assert_ne!(old_deep_decl, old_glob_decl);
@@ -436,7 +436,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 match (old_decl.is_glob_import(), decl.is_glob_import()) {
                     (true, true) => {
                         resolution.glob_decl =
-                            Some(this.select_glob_decl(decl, old_decl, warn_ambiguity));
+                            Some(this.select_glob_decl(old_decl, decl, warn_ambiguity));
                     }
                     (old_glob @ true, false) | (old_glob @ false, true) => {
                         let (glob_decl, non_glob_decl) =
@@ -446,7 +446,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                             && old_glob_decl != glob_decl
                         {
                             resolution.glob_decl =
-                                Some(this.select_glob_decl(glob_decl, old_glob_decl, false));
+                                Some(this.select_glob_decl(old_glob_decl, glob_decl, false));
                         } else {
                             resolution.glob_decl = Some(glob_decl);
                         }

tests/ui/hygiene/cross-crate-redefine.rs

@@ -8,7 +8,7 @@ extern crate use_by_macro;
 use use_by_macro::*;
 
 my_struct!(define);
-//~^ ERROR the name `MyStruct` is defined multiple times
 my_struct!(define);
+//~^ ERROR the name `MyStruct` is defined multiple times
 
 fn main() {}

tests/ui/hygiene/cross-crate-redefine.stderr

@@ -1,11 +1,10 @@
 error[E0428]: the name `MyStruct` is defined multiple times
-  --> $DIR/cross-crate-redefine.rs:10:1
+  --> $DIR/cross-crate-redefine.rs:11:1
    |
-LL | my_struct!(define);
-   | ^^^^^^^^^^^^^^^^^^ `MyStruct` redefined here
-LL |
 LL | my_struct!(define);
    | ------------------ previous definition of the type `MyStruct` here
+LL | my_struct!(define);
+   | ^^^^^^^^^^^^^^^^^^ `MyStruct` redefined here
    |
    = note: `MyStruct` must be defined only once in the type namespace of this module
    = note: this error originates in the macro `my_struct` (in Nightly builds, run with -Z macro-backtrace for more info)