Rollup merge of #32849 - jseyfried:import_resolution_diagnostics, r=eddyb

resolve: import resolution diagnostics

This improves the diagnostics for failing import resolutions (fixes #32833).
r? @eddyb

Author: steveklabnik

src/librustc_resolve/resolve_imports.rs

@@ -539,6 +539,7 @@ impl<'a, 'b:'a, 'tcx:'b> ImportResolver<'a, 'b, 'tcx> {
             (&Failed(_), &Failed(_)) => {
                 let resolutions = target_module.resolutions.borrow();
                 let names = resolutions.iter().filter_map(|(&(ref name, _), resolution)| {
+                    if *name == source { return None; } // Never suggest the same name
                     match *resolution.borrow() {
                         NameResolution { binding: Some(_), .. } => Some(name),
                         NameResolution { single_imports: SingleImports::None, .. } => None,
@@ -549,9 +550,12 @@ impl<'a, 'b:'a, 'tcx:'b> ImportResolver<'a, 'b, 'tcx> {
                     Some(name) => format!(". Did you mean to use `{}`?", name),
                     None => "".to_owned(),
                 };
-                let msg = format!("There is no `{}` in `{}`{}",
-                                  source,
-                                  module_to_string(target_module), lev_suggestion);
+                let module_str = module_to_string(target_module);
+                let msg = if &module_str == "???" {
+                    format!("There is no `{}` in the crate root{}", source, lev_suggestion)
+                } else {
+                    format!("There is no `{}` in `{}`{}", source, module_str, lev_suggestion)
+                };
                 return Failed(Some((directive.span, msg)));
             }
             _ => (),

src/test/compile-fail/issue-32833.rs

@@ -0,0 +1,16 @@
+// Copyright 2016 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 bar::Foo; //~ ERROR There is no `Foo` in `bar` [E0432]
+mod bar {
+    use Foo; //~ ERROR There is no `Foo` in the crate root [E0432]
+}
+
+fn main() {}

src/test/compile-fail/use-mod-2.rs

@@ -10,10 +10,10 @@
 
 mod foo {
     use self::{self};
-    //~^ ERROR unresolved import `self`. There is no `self` in `???`
+    //~^ ERROR unresolved import `self`. There is no `self` in the crate root
 
     use super::{self};
-    //~^ ERROR unresolved import `super`. There is no `super` in `???`
+    //~^ ERROR unresolved import `super`. There is no `super` in the crate root
 }
 
 fn main() {}