Merge #4227

4227: Report invalid, nested, multi-segment crate-paths r=matklad a=djrenren

There was a bug in the previous path-validating code that didn't detect multi-segment paths that started with `crate`.

```rust
// Successfully reported
use foo::{crate};

// BUG: was not being reported
use foo::{crate::bar};
```

This was due to my confusion about path-associativity. That is, the path with no qualifier is the innermost path, not the outermost. I've updated the code with a lot of comments to explain what's going on. 

This bug was discovered when I found an erroneous `ok` test which I reported here: 
https://github.com/rust-analyzer/rust-analyzer/issues/4226

This test now fails and has been modified, hopefully in the spirit of the original test, to be correct.  Sorry about submitting the bug in the first place!

Co-authored-by: John Renner <[email protected]>

1 files changed, 1 insertions, 1 deletions

diff --git a/crates/ra_parser/src/grammar/items/use_item.rs b/crates/ra_parser/src/grammar/items/use_item.rs
index e3b991c8c..3a0c7a31a 100644
--- a/crates/ra_parser/src/grammar/items/use_item.rs
+++ b/crates/ra_parser/src/grammar/items/use_item.rs
@@ -47,7 +47,7 @@ fn use_tree(p: &mut Parser, top_level: bool) {
         // use {crate::path::from::root, or::path::from::crate_name}; // Rust 2018 (with a crate named `or`)
         // use {path::from::root}; // Rust 2015
         // use ::{some::arbritrary::path}; // Rust 2015
-        // use ::{{{crate::export}}}; // Nonsensical but perfectly legal nestnig
+        // use ::{{{root::export}}}; // Nonsensical but perfectly legal nesting
         T!['{'] => {
             use_tree_list(p);
         }