8 files changed, 64 insertions, 13 deletions

diff --git a/Cargo.lock b/Cargo.lock
index e29ff898d..478c706be 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1070,6 +1070,7 @@ dependencies = [
  "drop_bomb",
  "either",
  "insta",
+ "itertools",
  "log",
  "once_cell",
  "ra_arena",
diff --git a/crates/ra_hir_def/Cargo.toml b/crates/ra_hir_def/Cargo.toml
index 1efa00fe0..6b9be9948 100644
--- a/crates/ra_hir_def/Cargo.toml
+++ b/crates/ra_hir_def/Cargo.toml
@@ -14,6 +14,7 @@ rustc-hash = "1.0"
 either = "1.5"
 anymap = "0.12"
 drop_bomb = "0.1.4"
+itertools = "0.8.2"
 
 ra_arena = { path = "../ra_arena" }
 ra_db = { path = "../ra_db" }
diff --git a/crates/ra_hir_def/src/body/lower.rs b/crates/ra_hir_def/src/body/lower.rs
index e656f9a41..5c779521b 100644
--- a/crates/ra_hir_def/src/body/lower.rs
+++ b/crates/ra_hir_def/src/body/lower.rs
@@ -8,7 +8,7 @@ use ra_arena::Arena;
 use ra_syntax::{
     ast::{
         self, ArgListOwner, ArrayExprKind, LiteralKind, LoopBodyOwner, ModuleItemOwner, NameOwner,
-        TypeAscriptionOwner,
+        SlicePatComponents, TypeAscriptionOwner,
     },
     AstNode, AstPtr,
 };
@@ -591,7 +591,7 @@ where
                 let args = p.args().map(|p| self.collect_pat(p)).collect();
                 Pat::Tuple(args)
             }
-            ast::Pat::PlaceholderPat(_) => Pat::Wild,
+            ast::Pat::PlaceholderPat(_) | ast::Pat::DotDotPat(_) => Pat::Wild,
             ast::Pat::RecordPat(p) => {
                 let path = p.path().and_then(|path| self.expander.parse_path(path));
                 let record_field_pat_list =
@@ -616,12 +616,20 @@ where
 
                 Pat::Record { path, args: fields }
             }
+            ast::Pat::SlicePat(p) => {
+                let SlicePatComponents { prefix, slice, suffix } = p.components();
+
+                Pat::Slice {
+                    prefix: prefix.into_iter().map(|p| self.collect_pat(p)).collect(),
+                    slice: slice.map(|p| self.collect_pat(p)),
+                    suffix: suffix.into_iter().map(|p| self.collect_pat(p)).collect(),
+                }
+            }
 
             // FIXME: implement
-            ast::Pat::DotDotPat(_) => Pat::Missing,
             ast::Pat::BoxPat(_) => Pat::Missing,
             ast::Pat::LiteralPat(_) => Pat::Missing,
-            ast::Pat::SlicePat(_) | ast::Pat::RangePat(_) => Pat::Missing,
+            ast::Pat::RangePat(_) => Pat::Missing,
         };
         let ptr = AstPtr::new(&pat);
         self.alloc_pat(pattern, Either::Left(ptr))
diff --git a/crates/ra_hir_def/src/expr.rs b/crates/ra_hir_def/src/expr.rs
index a75ef9970..035824403 100644
--- a/crates/ra_hir_def/src/expr.rs
+++ b/crates/ra_hir_def/src/expr.rs
@@ -393,7 +393,7 @@ pub enum Pat {
     },
     Slice {
         prefix: Vec<PatId>,
-        rest: Option<PatId>,
+        slice: Option<PatId>,
         suffix: Vec<PatId>,
     },
     Path(Path),
@@ -424,8 +424,8 @@ impl Pat {
                 args.iter().copied().for_each(f);
             }
             Pat::Ref { pat, .. } => f(*pat),
-            Pat::Slice { prefix, rest, suffix } => {
-                let total_iter = prefix.iter().chain(rest.iter()).chain(suffix.iter());
+            Pat::Slice { prefix, slice, suffix } => {
+                let total_iter = prefix.iter().chain(slice.iter()).chain(suffix.iter());
                 total_iter.copied().for_each(f);
             }
             Pat::Record { args, .. } => {
diff --git a/crates/ra_syntax/src/ast.rs b/crates/ra_syntax/src/ast.rs
index 89cb9a9f3..d3e8888bd 100644
--- a/crates/ra_syntax/src/ast.rs
+++ b/crates/ra_syntax/src/ast.rs
@@ -18,7 +18,8 @@ use crate::{
 pub use self::{
     expr_extensions::{ArrayExprKind, BinOp, ElseBranch, LiteralKind, PrefixOp, RangeOp},
     extensions::{
-        FieldKind, PathSegmentKind, SelfParamKind, StructKind, TypeBoundKind, VisibilityKind,
+        FieldKind, PathSegmentKind, SelfParamKind, SlicePatComponents, StructKind, TypeBoundKind,
+        VisibilityKind,
     },
     generated::*,
     tokens::*,
diff --git a/crates/ra_syntax/src/ast/extensions.rs b/crates/ra_syntax/src/ast/extensions.rs
index cb0aee422..7dcf084de 100644
--- a/crates/ra_syntax/src/ast/extensions.rs
+++ b/crates/ra_syntax/src/ast/extensions.rs
@@ -1,6 +1,8 @@
 //! Various extension methods to ast Nodes, which are hard to code-generate.
 //! Extensions for various expressions live in a sibling `expr_extensions` module.
 
+use itertools::Itertools;
+
 use crate::{
     ast::{self, child_opt, children, AstNode, AttrInput, SyntaxNode},
     SmolStr, SyntaxElement,
@@ -293,6 +295,40 @@ impl ast::BindPat {
     }
 }
 
+pub struct SlicePatComponents {
+    pub prefix: Vec<ast::Pat>,
+    pub slice: Option<ast::Pat>,
+    pub suffix: Vec<ast::Pat>,
+}
+
+impl ast::SlicePat {
+    pub fn components(&self) -> SlicePatComponents {
+        let mut args = self.args().peekable();
+        let prefix = args
+            .peeking_take_while(|p| match p {
+                ast::Pat::DotDotPat(_) => false,
+                ast::Pat::BindPat(bp) => match bp.pat() {
+                    Some(ast::Pat::DotDotPat(_)) => false,
+                    _ => true,
+                },
+                ast::Pat::RefPat(rp) => match rp.pat() {
+                    Some(ast::Pat::DotDotPat(_)) => false,
+                    Some(ast::Pat::BindPat(bp)) => match bp.pat() {
+                        Some(ast::Pat::DotDotPat(_)) => false,
+                        _ => true,
+                    },
+                    _ => true,
+                },
+                _ => true,
+            })
+            .collect();
+        let slice = args.next();
+        let suffix = args.collect();
+
+        SlicePatComponents { prefix, slice, suffix }
+    }
+}
+
 impl ast::PointerType {
     pub fn is_mut(&self) -> bool {
         self.syntax().children_with_tokens().any(|n| n.kind() == T![mut])
diff --git a/crates/ra_syntax/src/ast/generated.rs b/crates/ra_syntax/src/ast/generated.rs
index 33d5578e7..8a3669bd1 100644
--- a/crates/ra_syntax/src/ast/generated.rs
+++ b/crates/ra_syntax/src/ast/generated.rs
@@ -2063,7 +2063,11 @@ impl AstNode for SlicePat {
         &self.syntax
     }
 }
-impl SlicePat {}
+impl SlicePat {
+    pub fn args(&self) -> AstChildren<Pat> {
+        AstChildren::new(&self.syntax)
+    }
+}
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct RangePat {
     pub(crate) syntax: SyntaxNode,
diff --git a/xtask/src/ast_src.rs b/xtask/src/ast_src.rs
index 67d1f41bc..efe1e795b 100644
--- a/xtask/src/ast_src.rs
+++ b/xtask/src/ast_src.rs
@@ -415,14 +415,14 @@ pub(crate) const AST_SRC: AstSrc = AstSrc {
             pats: [Pat],
             guard: MatchGuard,
             Expr,
-         }
+        }
         struct MatchGuard { Expr }
 
         struct RecordLit { Path, RecordFieldList }
         struct RecordFieldList {
             fields: [RecordField],
             spread: Expr,
-         }
+        }
         struct RecordField { NameRef, Expr }
 
         struct RefPat { Pat }
@@ -430,8 +430,8 @@ pub(crate) const AST_SRC: AstSrc = AstSrc {
         struct BindPat: NameOwner { Pat }
         struct PlaceholderPat { }
         struct DotDotPat { }
-        struct PathPat {  Path }
-        struct SlicePat {}
+        struct PathPat { Path }
+        struct SlicePat { args: [Pat] }
         struct RangePat {}
         struct LiteralPat { Literal }