WIP: rewrite build_reduced_graph_for_use_tree

Author: mu001999

compiler/rustc_resolve/messages.ftl

@@ -463,6 +463,9 @@ resolve_unexpected_res_use_at_op_in_slice_pat_with_range_sugg =
 resolve_unnamed_crate_root_import =
     crate root imports need to be explicitly named: `use crate as name;`
 
+resolve_unnamed_imports =
+    imports need to be explicitly named: `use {$ident} as name;`
+
 resolve_unreachable_label =
     use of unreachable label `{$name}`
     .label = unreachable label `{$name}`

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -594,8 +594,29 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                         }
                     }
                 } else {
+                    if matches!(source.ident.name, kw::Crate | kw::Super) {
+                        // Disallow `use foo::crate;` and `use crate::crate;`
+                        if !module_path.is_empty() {
+                            // FIXME: use other errors
+                            self.r
+                                .dcx()
+                                .emit_err(errors::UnnamedImports { span: ident.span, ident });
+                            return;
+                        }
+
+                        // Disallow `use crate;` and `use super;`
+                        if rename.is_none() {
+                            self.r
+                                .dcx()
+                                .emit_err(errors::UnnamedImports { span: ident.span, ident });
+                            return;
+                        }
+
+                        // Allow `use super as name;`
+                        type_ns_only = true;
+                    }
                     // Disallow `self`
-                    if source.ident.name == kw::SelfLower {
+                    else if source.ident.name == kw::SelfLower {
                         let parent = module_path.last();
 
                         let span = match parent {
@@ -706,6 +727,12 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                     }
 
                     e.emit();
+                } else if let &[self_span] = &self_spans[..]
+                    && prefix.len() == 1
+                    && prefix[0].ident.name == kw::DollarCrate
+                {
+                    // Disallow `use $crate::{self};`
+                    self.r.dcx().emit_err(errors::CrateImported { span: self_span });
                 }
 
                 for &(ref tree, id) in items {

compiler/rustc_resolve/src/errors.rs

@@ -898,6 +898,14 @@ pub(crate) struct UnnamedCrateRootImport {
     pub(crate) span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(resolve_unnamed_imports)]
+pub(crate) struct UnnamedImports {
+    #[primary_span]
+    pub(crate) span: Span,
+    pub(crate) ident: Ident,
+}
+
 #[derive(Diagnostic)]
 #[diag(resolve_macro_expanded_extern_crate_cannot_shadow_extern_arguments)]
 pub(crate) struct MacroExpandedExternCrateCannotShadowExternArguments {

compiler/rustc_resolve/src/ident.rs

@@ -861,6 +861,14 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         // FIXME: Implement these with renaming requirements so that e.g.
                         // `use super;` doesn't work, but `use super as name;` does.
                         // Fall through here to get an error from `early_resolve_...`.
+
+                        if ident.name == kw::Super {
+                            if let Some(parent) = parent_scope.module.parent {
+                                return Ok(parent.self_binding.unwrap());
+                            }
+                        } else {
+                            return Ok(parent_scope.module.self_binding.unwrap());
+                        }
                     }
                 }
 

tests/ui/dollar-crate/use-dollar-crate-self.rs

@@ -0,0 +1,9 @@
+macro_rules! foo {
+    () => {
+        use $crate::{self}; //~ ERROR `$crate` may not be imported
+    };
+}
+
+foo!();
+
+fn main() {}

tests/ui/dollar-crate/use-dollar-crate-self.stderr

@@ -0,0 +1,13 @@
+error: `$crate` may not be imported
+  --> $DIR/use-dollar-crate-self.rs:3:22
+   |
+LL |         use $crate::{self};
+   |                      ^^^^
+...
+LL | foo!();
+   | ------ in this macro invocation
+   |
+   = note: this error originates in the macro `foo` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 1 previous error
+

tests/ui/use/use-path-segment-kw.rs

@@ -0,0 +1,35 @@
+// mod x {
+//     use super; // bad
+//     use super as name; // good
+//     use self; // bad
+//     use self as name; // good
+//     use crate; // bad
+//     use crate as name; // good
+
+//     mod y;
+//     use y::crate; // bad
+//     use crate::crate; // bad
+
+//     // use $crate; // bad
+//     // use $crate as name; // good
+
+//     // use super::{self}; // bad
+//     // use super::{self as name}; // good
+//     // use crate::{self}; // bad
+//     // use crate::{self as name}; // good
+//     // use $crate::{self}; // bad
+//     // use $crate::{self as name}; // good
+// }
+
+mod foo {
+    pub mod foobar {
+        pub use super as x;
+    }
+    pub fn bar() {
+        println!("hello");
+    }
+}
+
+fn main() {
+    foo::foobar::x::bar();
+}