Merge #1733

1733: Parse arbitrarily complex `box` patterns. r=matklad a=ecstatic-morse

This fully resolves the pattern part of #1412 by enabling the parsing of complex `box` patterns such as:

```rust
let box Struct { box i, j: box Inner(box &x) } = todo!();
```

This introduces a new `ast::BoxPat` (in the mold of `ast::RefPat`) that gets translated to `hir::Pat::Missing`.

Co-authored-by: Dylan MacKenzie <[email protected]>

3 files changed, 31 insertions, 21 deletions

diff --git a/crates/ra_parser/src/grammar/expressions/atom.rs b/crates/ra_parser/src/grammar/expressions/atom.rs
index ab8fb9f6e..bc942ae01 100644
--- a/crates/ra_parser/src/grammar/expressions/atom.rs
+++ b/crates/ra_parser/src/grammar/expressions/atom.rs
@@ -414,8 +414,6 @@ pub(crate) fn match_arm_list(p: &mut Parser) {
 //         X | Y if Z => (),
 //         | X | Y if Z => (),
 //         | X => (),
-//         box X => (),
-//         Some(box X) => (),
 //     };
 // }
 fn match_arm(p: &mut Parser) -> BlockLike {
diff --git a/crates/ra_parser/src/grammar/patterns.rs b/crates/ra_parser/src/grammar/patterns.rs
index 8979aa499..eae70ab85 100644
--- a/crates/ra_parser/src/grammar/patterns.rs
+++ b/crates/ra_parser/src/grammar/patterns.rs
@@ -56,37 +56,33 @@ const PAT_RECOVERY_SET: TokenSet =
     token_set![LET_KW, IF_KW, WHILE_KW, LOOP_KW, MATCH_KW, R_PAREN, COMMA];
 
 fn atom_pat(p: &mut Parser, recovery_set: TokenSet) -> Option<CompletedMarker> {
-    let la0 = p.nth(0);
-    let la1 = p.nth(1);
-    if la0 == T![ref]
-        || la0 == T![mut]
-        || la0 == T![box]
-        || (la0 == IDENT && !(la1 == T![::] || la1 == T!['('] || la1 == T!['{'] || la1 == T![!]))
-    {
-        return Some(bind_pat(p, true));
-    }
-    if paths::is_use_path_start(p) {
-        return Some(path_pat(p));
-    }
+    // Checks the token after an IDENT to see if a pattern is a path (Struct { .. }) or macro
+    // (T![x]).
+    let is_path_or_macro_pat =
+        |la1| la1 == T![::] || la1 == T!['('] || la1 == T!['{'] || la1 == T![!];
 
-    if is_literal_pat_start(p) {
-        return Some(literal_pat(p));
-    }
+    let m = match p.nth(0) {
+        T![box] => box_pat(p),
+        T![ref] | T![mut] | IDENT if !is_path_or_macro_pat(p.nth(1)) => bind_pat(p, true),
+
+        _ if paths::is_use_path_start(p) => path_pat(p),
+        _ if is_literal_pat_start(p) => literal_pat(p),
 
-    let m = match la0 {
         T![_] => placeholder_pat(p),
         T![&] => ref_pat(p),
         T!['('] => tuple_pat(p),
         T!['['] => slice_pat(p),
+
         _ => {
             p.err_recover("expected pattern", recovery_set);
             return None;
         }
     };
+
     Some(m)
 }
 
-fn is_literal_pat_start(p: &mut Parser) -> bool {
+fn is_literal_pat_start(p: &Parser) -> bool {
     p.at(T![-]) && (p.nth(1) == INT_NUMBER || p.nth(1) == FLOAT_NUMBER)
         || p.at_ts(expressions::LITERAL_FIRST)
 }
@@ -165,6 +161,9 @@ fn record_field_pat_list(p: &mut Parser) {
             T![..] => p.bump(),
             IDENT if p.nth(1) == T![:] => record_field_pat(p),
             T!['{'] => error_block(p, "expected ident"),
+            T![box] => {
+                box_pat(p);
+            }
             _ => {
                 bind_pat(p, false);
             }
@@ -261,11 +260,9 @@ fn pat_list(p: &mut Parser, ket: SyntaxKind) {
 //     let ref mut d = ();
 //     let e @ _ = ();
 //     let ref mut f @ g @ _ = ();
-//     let box i = Box::new(1i32);
 // }
 fn bind_pat(p: &mut Parser, with_at: bool) -> CompletedMarker {
     let m = p.start();
-    p.eat(T![box]);
     p.eat(T![ref]);
     p.eat(T![mut]);
     name(p);
@@ -274,3 +271,17 @@ fn bind_pat(p: &mut Parser, with_at: bool) -> CompletedMarker {
     }
     m.complete(p, BIND_PAT)
 }
+
+// test box_pat
+// fn main() {
+//     let box i = ();
+//     let box Outer { box i, j: box Inner(box &x) } = ();
+//     let box ref mut i = ();
+// }
+fn box_pat(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(T![box]));
+    let m = p.start();
+    p.bump();
+    pattern(p);
+    m.complete(p, BOX_PAT)
+}
diff --git a/crates/ra_parser/src/syntax_kind/generated.rs b/crates/ra_parser/src/syntax_kind/generated.rs
index f15e98e68..8ba29ebf8 100644
--- a/crates/ra_parser/src/syntax_kind/generated.rs
+++ b/crates/ra_parser/src/syntax_kind/generated.rs
@@ -149,6 +149,7 @@ pub enum SyntaxKind {
     IMPL_TRAIT_TYPE,
     DYN_TRAIT_TYPE,
     REF_PAT,
+    BOX_PAT,
     BIND_PAT,
     PLACEHOLDER_PAT,
     PATH_PAT,