Disable use $crate::{self}

Author: mu001999

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -706,6 +706,12 @@ 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 {

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
+