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]>

2 files changed, 40 insertions, 2 deletions

diff --git a/crates/ra_syntax/src/ast/generated.rs b/crates/ra_syntax/src/ast/generated.rs
index 07cc3e0db..90480b6ca 100644
--- a/crates/ra_syntax/src/ast/generated.rs
+++ b/crates/ra_syntax/src/ast/generated.rs
@@ -307,6 +307,33 @@ impl BlockExpr {
     }
 }
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct BoxPat {
+    pub(crate) syntax: SyntaxNode,
+}
+impl AstNode for BoxPat {
+    fn can_cast(kind: SyntaxKind) -> bool {
+        match kind {
+            BOX_PAT => true,
+            _ => false,
+        }
+    }
+    fn cast(syntax: SyntaxNode) -> Option<Self> {
+        if Self::can_cast(syntax.kind()) {
+            Some(Self { syntax })
+        } else {
+            None
+        }
+    }
+    fn syntax(&self) -> &SyntaxNode {
+        &self.syntax
+    }
+}
+impl BoxPat {
+    pub fn pat(&self) -> Option<Pat> {
+        AstChildren::new(&self.syntax).next()
+    }
+}
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct BreakExpr {
     pub(crate) syntax: SyntaxNode,
 }
@@ -2063,6 +2090,7 @@ impl ParenType {
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub enum Pat {
     RefPat(RefPat),
+    BoxPat(BoxPat),
     BindPat(BindPat),
     PlaceholderPat(PlaceholderPat),
     PathPat(PathPat),
@@ -2078,6 +2106,11 @@ impl From<RefPat> for Pat {
         Pat::RefPat(node)
     }
 }
+impl From<BoxPat> for Pat {
+    fn from(node: BoxPat) -> Pat {
+        Pat::BoxPat(node)
+    }
+}
 impl From<BindPat> for Pat {
     fn from(node: BindPat) -> Pat {
         Pat::BindPat(node)
@@ -2126,14 +2159,15 @@ impl From<LiteralPat> for Pat {
 impl AstNode for Pat {
     fn can_cast(kind: SyntaxKind) -> bool {
         match kind {
-            REF_PAT | BIND_PAT | PLACEHOLDER_PAT | PATH_PAT | RECORD_PAT | TUPLE_STRUCT_PAT
-            | TUPLE_PAT | SLICE_PAT | RANGE_PAT | LITERAL_PAT => true,
+            REF_PAT | BOX_PAT | BIND_PAT | PLACEHOLDER_PAT | PATH_PAT | RECORD_PAT
+            | TUPLE_STRUCT_PAT | TUPLE_PAT | SLICE_PAT | RANGE_PAT | LITERAL_PAT => true,
             _ => false,
         }
     }
     fn cast(syntax: SyntaxNode) -> Option<Self> {
         let res = match syntax.kind() {
             REF_PAT => Pat::RefPat(RefPat { syntax }),
+            BOX_PAT => Pat::BoxPat(BoxPat { syntax }),
             BIND_PAT => Pat::BindPat(BindPat { syntax }),
             PLACEHOLDER_PAT => Pat::PlaceholderPat(PlaceholderPat { syntax }),
             PATH_PAT => Pat::PathPat(PathPat { syntax }),
@@ -2150,6 +2184,7 @@ impl AstNode for Pat {
     fn syntax(&self) -> &SyntaxNode {
         match self {
             Pat::RefPat(it) => &it.syntax,
+            Pat::BoxPat(it) => &it.syntax,
             Pat::BindPat(it) => &it.syntax,
             Pat::PlaceholderPat(it) => &it.syntax,
             Pat::PathPat(it) => &it.syntax,
diff --git a/crates/ra_syntax/src/grammar.ron b/crates/ra_syntax/src/grammar.ron
index 4659192cd..1836862fe 100644
--- a/crates/ra_syntax/src/grammar.ron
+++ b/crates/ra_syntax/src/grammar.ron
@@ -158,6 +158,7 @@ Grammar(
         "DYN_TRAIT_TYPE",
 
         "REF_PAT",
+        "BOX_PAT",
         "BIND_PAT",
         "PLACEHOLDER_PAT",
         "PATH_PAT",
@@ -523,6 +524,7 @@ Grammar(
         ),
 
         "RefPat": ( options: [ "Pat" ]),
+        "BoxPat": ( options: [ "Pat" ]),
         "BindPat": (
             options: [ "Pat" ],
             traits: ["NameOwner"]
@@ -552,6 +554,7 @@ Grammar(
         "Pat": (
             enum: [
                 "RefPat",
+                "BoxPat",
                 "BindPat",
                 "PlaceholderPat",
                 "PathPat",