Merge #7994

7994: Speed up mbe matching in heavy recursive cases r=edwin0cheng a=edwin0cheng

In some cases (e.g.  #4186), mbe matching is very slow due to a lot of copy and allocation for bindings, this PR try to solve this problem by introduce a semi "link-list" approach for bindings building.

I used this [test case](https://github.com/weiznich/minimal_example_for_rust_81262) (for `features(32-column-tables)`) to run following command to benchmark:
```
time rust-analyzer analysis-stats  --load-output-dirs ./ 
```

Before this PR : 2 mins
After this PR: 3 seconds.

However, for 64-column-tables cases, we still need 4 mins to complete. 

I will try to investigate in the following weeks.

bors r+




Co-authored-by: Edwin Cheng <[email protected]>

1 files changed, 2 insertions, 0 deletions

diff --git a/crates/hir_expand/src/db.rs b/crates/hir_expand/src/db.rs
index cb6e23320..9086e6c17 100644
--- a/crates/hir_expand/src/db.rs
+++ b/crates/hir_expand/src/db.rs
@@ -340,6 +340,8 @@ fn parse_macro_with_arg(
         None => return ExpandResult { value: None, err: result.err },
     };
 
+    log::debug!("expanded = {}", tt.as_debug_string());
+
     let fragment_kind = to_fragment_kind(db, macro_call_id);
 
     let (parse, rev_token_map) = match mbe::token_tree_to_syntax_node(&tt, fragment_kind) {