16 files changed, 263 insertions, 27 deletions

diff --git a/crates/libeditor/src/lib.rs b/crates/libeditor/src/lib.rs
index d39e56d81..34056b3c0 100644
--- a/crates/libeditor/src/lib.rs
+++ b/crates/libeditor/src/lib.rs
@@ -27,7 +27,7 @@ pub use self::{
         ActionResult,
         flip_comma, add_derive, add_impl,
     },
-    typing::join_lines,
+    typing::{join_lines, on_eq_typed},
     completion::scope_completion,
 };
 
diff --git a/crates/libeditor/src/typing.rs b/crates/libeditor/src/typing.rs
index 060095f28..48a8d6bb0 100644
--- a/crates/libeditor/src/typing.rs
+++ b/crates/libeditor/src/typing.rs
@@ -7,11 +7,11 @@ use libsyntax2::{
         walk::preorder,
         find_covering_node,
     },
-    text_utils::intersect,
+    text_utils::{intersect, contains_offset_nonstrict},
     SyntaxKind::*,
 };
 
-use {ActionResult, EditBuilder};
+use {ActionResult, EditBuilder, find_node_at_offset};
 
 pub fn join_lines(file: &File, range: TextRange) -> ActionResult {
     let range = if range.is_empty() {
@@ -56,6 +56,26 @@ pub fn join_lines(file: &File, range: TextRange) -> ActionResult {
     }
 }
 
+pub fn on_eq_typed(file: &File, offset: TextUnit) -> Option<ActionResult> {
+    let let_stmt: ast::LetStmt = find_node_at_offset(file.syntax(), offset)?;
+    if let_stmt.has_semi() {
+        return None;
+    }
+    if let Some(expr) = let_stmt.initializer() {
+        let expr_range = expr.syntax().range();
+        if contains_offset_nonstrict(expr_range, offset) && offset != expr_range.start() {
+            return None;
+        }
+    }
+    let offset = let_stmt.syntax().range().end();
+    let mut edit = EditBuilder::new();
+    edit.insert(offset, ";".to_string());
+    Some(ActionResult {
+        edit: edit.finish(),
+        cursor_position: None,
+    })
+}
+
 fn remove_newline(
     edit: &mut EditBuilder,
     node: SyntaxNodeRef,
diff --git a/crates/libeditor/tests/test.rs b/crates/libeditor/tests/test.rs
index d8c24610d..17926d5ae 100644
--- a/crates/libeditor/tests/test.rs
+++ b/crates/libeditor/tests/test.rs
@@ -9,7 +9,7 @@ use libeditor::{
     ActionResult,
     highlight, runnables, extend_selection, file_structure,
     flip_comma, add_derive, add_impl, matching_brace,
-    join_lines, scope_completion,
+    join_lines, on_eq_typed, scope_completion,
 };
 
 #[test]
@@ -227,7 +227,7 @@ pub fn reparse(&self, edit: &AtomEdit) -> File {
 #[test]
 fn test_join_lines_selection() {
     fn do_check(before: &str, after: &str) {
-        let (sel, before) = extract_range(&before);
+        let (sel, before) = extract_range(before);
         let file = file(&before);
         let result = join_lines(&file, sel);
         let actual = result.edit.apply(&before);
@@ -257,6 +257,48 @@ struct Foo { f: u32 }
 }
 
 #[test]
+fn test_on_eq_typed() {
+    fn do_check(before: &str, after: &str) {
+        let (offset, before) = extract_offset(before);
+        let file = file(&before);
+        let result = on_eq_typed(&file, offset).unwrap();
+        let actual = result.edit.apply(&before);
+        assert_eq_text!(after, &actual);
+    }
+
+    do_check(r"
+fn foo() {
+    let foo =<|>
+}
+", r"
+fn foo() {
+    let foo =;
+}
+");
+    do_check(r"
+fn foo() {
+    let foo =<|> 1 + 1
+}
+", r"
+fn foo() {
+    let foo = 1 + 1;
+}
+");
+//     do_check(r"
+// fn foo() {
+//     let foo =<|>
+//     let bar = 1;
+// }
+// ", r"
+// fn foo() {
+//     let foo =;
+//     let bar = 1;
+// }
+// ");
+
+}
+
+#[test]
 fn test_completion() {
     fn do_check(code: &str, expected_completions: &str) {
         let (off, code) = extract_offset(&code);
diff --git a/crates/libsyntax2/src/ast/generated.rs b/crates/libsyntax2/src/ast/generated.rs
index f99d1274a..6181aada8 100644
--- a/crates/libsyntax2/src/ast/generated.rs
+++ b/crates/libsyntax2/src/ast/generated.rs
@@ -439,6 +439,24 @@ impl<'a> ExprStmt<'a> {
     }
 }
 
+// ExternCrateItem
+#[derive(Debug, Clone, Copy)]
+pub struct ExternCrateItem<'a> {
+    syntax: SyntaxNodeRef<'a>,
+}
+
+impl<'a> AstNode<'a> for ExternCrateItem<'a> {
+    fn cast(syntax: SyntaxNodeRef<'a>) -> Option<Self> {
+        match syntax.kind() {
+            EXTERN_CRATE_ITEM => Some(ExternCrateItem { syntax }),
+            _ => None,
+        }
+    }
+    fn syntax(self) -> SyntaxNodeRef<'a> { self.syntax }
+}
+
+impl<'a> ExternCrateItem<'a> {}
+
 // FieldExpr
 #[derive(Debug, Clone, Copy)]
 pub struct FieldExpr<'a> {
@@ -839,11 +857,51 @@ impl<'a> AstNode<'a> for Module<'a> {
 impl<'a> ast::NameOwner<'a> for Module<'a> {}
 impl<'a> ast::AttrsOwner<'a> for Module<'a> {}
 impl<'a> Module<'a> {
-    pub fn modules(self) -> impl Iterator<Item = Module<'a>> + 'a {
+    pub fn items(self) -> impl Iterator<Item = ModuleItem<'a>> + 'a {
         super::children(self)
     }
 }
 
+// ModuleItem
+#[derive(Debug, Clone, Copy)]
+pub enum ModuleItem<'a> {
+    StructDef(StructDef<'a>),
+    EnumDef(EnumDef<'a>),
+    FnDef(FnDef<'a>),
+    TraitDef(TraitDef<'a>),
+    ImplItem(ImplItem<'a>),
+    UseItem(UseItem<'a>),
+    ExternCrateItem(ExternCrateItem<'a>),
+}
+
+impl<'a> AstNode<'a> for ModuleItem<'a> {
+    fn cast(syntax: SyntaxNodeRef<'a>) -> Option<Self> {
+        match syntax.kind() {
+            STRUCT_DEF => Some(ModuleItem::StructDef(StructDef { syntax })),
+            ENUM_DEF => Some(ModuleItem::EnumDef(EnumDef { syntax })),
+            FN_DEF => Some(ModuleItem::FnDef(FnDef { syntax })),
+            TRAIT_DEF => Some(ModuleItem::TraitDef(TraitDef { syntax })),
+            IMPL_ITEM => Some(ModuleItem::ImplItem(ImplItem { syntax })),
+            USE_ITEM => Some(ModuleItem::UseItem(UseItem { syntax })),
+            EXTERN_CRATE_ITEM => Some(ModuleItem::ExternCrateItem(ExternCrateItem { syntax })),
+            _ => None,
+        }
+    }
+    fn syntax(self) -> SyntaxNodeRef<'a> {
+        match self {
+            ModuleItem::StructDef(inner) => inner.syntax(),
+            ModuleItem::EnumDef(inner) => inner.syntax(),
+            ModuleItem::FnDef(inner) => inner.syntax(),
+            ModuleItem::TraitDef(inner) => inner.syntax(),
+            ModuleItem::ImplItem(inner) => inner.syntax(),
+            ModuleItem::UseItem(inner) => inner.syntax(),
+            ModuleItem::ExternCrateItem(inner) => inner.syntax(),
+        }
+    }
+}
+
+impl<'a> ModuleItem<'a> {}
+
 // Name
 #[derive(Debug, Clone, Copy)]
 pub struct Name<'a> {
@@ -1762,6 +1820,24 @@ impl<'a> AstNode<'a> for TypeRef<'a> {
 
 impl<'a> TypeRef<'a> {}
 
+// UseItem
+#[derive(Debug, Clone, Copy)]
+pub struct UseItem<'a> {
+    syntax: SyntaxNodeRef<'a>,
+}
+
+impl<'a> AstNode<'a> for UseItem<'a> {
+    fn cast(syntax: SyntaxNodeRef<'a>) -> Option<Self> {
+        match syntax.kind() {
+            USE_ITEM => Some(UseItem { syntax }),
+            _ => None,
+        }
+    }
+    fn syntax(self) -> SyntaxNodeRef<'a> { self.syntax }
+}
+
+impl<'a> UseItem<'a> {}
+
 // WhereClause
 #[derive(Debug, Clone, Copy)]
 pub struct WhereClause<'a> {
diff --git a/crates/libsyntax2/src/ast/mod.rs b/crates/libsyntax2/src/ast/mod.rs
index 2ebee6a4f..9941138a7 100644
--- a/crates/libsyntax2/src/ast/mod.rs
+++ b/crates/libsyntax2/src/ast/mod.rs
@@ -115,6 +115,15 @@ impl<'a> Module<'a> {
     }
 }
 
+impl<'a> LetStmt<'a> {
+    pub fn has_semi(self) -> bool {
+        match self.syntax().last_child() {
+            None => false,
+            Some(node) => node.kind() == SEMI,
+        }
+    }
+}
+
 impl<'a> IfExpr<'a> {
     pub fn then_branch(self) -> Option<Block<'a>> {
         self.blocks().nth(0)
diff --git a/crates/libsyntax2/src/grammar.ron b/crates/libsyntax2/src/grammar.ron
index a98e9e2fd..7217a4633 100644
--- a/crates/libsyntax2/src/grammar.ron
+++ b/crates/libsyntax2/src/grammar.ron
@@ -273,7 +273,7 @@ Grammar(
         "Module": (
             traits: ["NameOwner", "AttrsOwner"],
             collections: [
-                ["modules", "Module"]
+                ["items", "ModuleItem"]
             ]
         ),
         "ConstDef": ( traits: [
@@ -331,6 +331,10 @@ Grammar(
                 "AttrsOwner"
             ],
         ),
+        "ModuleItem": (
+            enum: ["StructDef", "EnumDef", "FnDef", "TraitDef", "ImplItem",
+                   "UseItem", "ExternCrateItem" ]
+        ),
 
         "TupleExpr": (),
         "ArrayExpr": (),
@@ -479,6 +483,8 @@ Grammar(
         ),
         "Param": (
             options: [["pat", "Pat"]],
-        )
+        ),
+        "UseItem": (),
+        "ExternCrateItem": (),
     },
 )
diff --git a/crates/libsyntax2/src/grammar/expressions/atom.rs b/crates/libsyntax2/src/grammar/expressions/atom.rs
index ab4aa49d2..0769bb5a8 100644
--- a/crates/libsyntax2/src/grammar/expressions/atom.rs
+++ b/crates/libsyntax2/src/grammar/expressions/atom.rs
@@ -33,6 +33,9 @@ pub(super) const ATOM_EXPR_FIRST: TokenSet =
                    RETURN_KW, IDENT, SELF_KW, SUPER_KW, COLONCOLON, BREAK_KW, CONTINUE_KW, LIFETIME ],
     ];
 
+const EXPR_RECOVERY_SET: TokenSet =
+    token_set![LET_KW];
+
 pub(super) fn atom_expr(p: &mut Parser, r: Restrictions) -> Option<CompletedMarker> {
     match literal(p) {
         Some(m) => return Some(m),
@@ -73,7 +76,7 @@ pub(super) fn atom_expr(p: &mut Parser, r: Restrictions) -> Option<CompletedMark
         CONTINUE_KW => continue_expr(p),
         BREAK_KW => break_expr(p),
         _ => {
-            p.err_and_bump("expected expression");
+            p.err_recover("expected expression", EXPR_RECOVERY_SET);
             return None;
         }
     };
diff --git a/crates/libsyntax2/src/parser_api.rs b/crates/libsyntax2/src/parser_api.rs
index 0a3b29b70..10b9b64ac 100644
--- a/crates/libsyntax2/src/parser_api.rs
+++ b/crates/libsyntax2/src/parser_api.rs
@@ -12,6 +12,8 @@ fn mask(kind: SyntaxKind) -> u128 {
 }
 
 impl TokenSet {
+    const EMPTY: TokenSet = TokenSet(0);
+
     pub fn contains(&self, kind: SyntaxKind) -> bool {
         self.0 & mask(kind) != 0
     }
@@ -139,12 +141,21 @@ impl<'t> Parser<'t> {
 
     /// Create an error node and consume the next token.
     pub(crate) fn err_and_bump(&mut self, message: &str) {
-        let m = self.start();
-        self.error(message);
-        if !self.at(SyntaxKind::L_CURLY) && !self.at(SyntaxKind::R_CURLY) {
+        self.err_recover(message, TokenSet::EMPTY);
+    }
+
+    /// Create an error node and consume the next token.
+    pub(crate) fn err_recover(&mut self, message: &str, recovery_set: TokenSet) {
+        if self.at(SyntaxKind::L_CURLY)
+            || self.at(SyntaxKind::R_CURLY)
+            || recovery_set.contains(self.current()) {
+            self.error(message);
+        } else {
+            let m = self.start();
+            self.error(message);
             self.bump();
+            m.complete(self, ERROR);
         }
-        m.complete(self, ERROR);
     }
 }
 
diff --git a/crates/libsyntax2/tests/data/parser/err/0017_incomplete_binexpr.txt b/crates/libsyntax2/tests/data/parser/err/0017_incomplete_binexpr.txt
index db9a2f175..f0be287ad 100644
--- a/crates/libsyntax2/tests/data/parser/err/0017_incomplete_binexpr.txt
+++ b/crates/libsyntax2/tests/data/parser/err/0017_incomplete_binexpr.txt
@@ -35,13 +35,12 @@ ROOT@[0; 47)
           INT_NUMBER@[33; 35) "92"
         SEMI@[35; 36)
       WHITESPACE@[36; 41)
-      BIN_EXPR@[41; 45)
+      BIN_EXPR@[41; 44)
         LITERAL@[41; 42)
           INT_NUMBER@[41; 42) "1"
         WHITESPACE@[42; 43)
         PLUS@[43; 44)
-        WHITESPACE@[44; 45)
         err: `expected expression`
-        ERROR@[45; 45)
+      WHITESPACE@[44; 45)
       R_CURLY@[45; 46)
   WHITESPACE@[46; 47)
diff --git a/crates/libsyntax2/tests/data/parser/err/0018_incomplete_fn.txt b/crates/libsyntax2/tests/data/parser/err/0018_incomplete_fn.txt
index 3f3a7784b..58e39a341 100644
--- a/crates/libsyntax2/tests/data/parser/err/0018_incomplete_fn.txt
+++ b/crates/libsyntax2/tests/data/parser/err/0018_incomplete_fn.txt
@@ -11,12 +11,12 @@ ROOT@[0; 183)
     ITEM_LIST@[14; 182)
       L_CURLY@[14; 15)
       WHITESPACE@[15; 20)
-      FN_DEF@[20; 181)
+      FN_DEF@[20; 180)
         FN_KW@[20; 22)
         WHITESPACE@[22; 23)
         NAME@[23; 32)
           IDENT@[23; 32) "new_scope"
-        PARAM_LIST@[32; 181)
+        PARAM_LIST@[32; 180)
           L_PAREN@[32; 33)
           PARAM@[33; 38)
             REF_PAT@[33; 35)
@@ -163,17 +163,16 @@ ROOT@[0; 183)
               err: `expected parameters`
               err: `expected COMMA`
           WHITESPACE@[169; 170)
-          PARAM@[170; 181)
+          PARAM@[170; 180)
             BIND_PAT@[170; 180)
               NAME@[170; 180)
                 IDENT@[170; 180) "set_parent"
                 err: `expected COLON`
-            WHITESPACE@[180; 181)
-            err: `expected type`
-            err: `expected COMMA`
-            err: `expected value parameter`
-            err: `expected R_PAREN`
-            err: `expected a block`
-            ERROR@[181; 181)
+                err: `expected type`
+                err: `expected COMMA`
+                err: `expected value parameter`
+                err: `expected R_PAREN`
+                err: `expected a block`
+      WHITESPACE@[180; 181)
       R_CURLY@[181; 182)
   WHITESPACE@[182; 183)
diff --git a/crates/libsyntax2/tests/data/parser/err/0019_let_recover.rs b/crates/libsyntax2/tests/data/parser/err/0019_let_recover.rs
new file mode 100644
index 000000000..52bddd494
--- /dev/null
+++ b/crates/libsyntax2/tests/data/parser/err/0019_let_recover.rs
@@ -0,0 +1,4 @@
+fn foo() {
+    let foo =
+    let bar = 1;
+}
diff --git a/crates/libsyntax2/tests/data/parser/err/0019_let_recover.txt b/crates/libsyntax2/tests/data/parser/err/0019_let_recover.txt
new file mode 100644
index 000000000..9ffa9d781
--- /dev/null
+++ b/crates/libsyntax2/tests/data/parser/err/0019_let_recover.txt
@@ -0,0 +1,39 @@
+ROOT@[0; 44)
+  FN_DEF@[0; 43)
+    FN_KW@[0; 2)
+    WHITESPACE@[2; 3)
+    NAME@[3; 6)
+      IDENT@[3; 6) "foo"
+    PARAM_LIST@[6; 8)
+      L_PAREN@[6; 7)
+      R_PAREN@[7; 8)
+    WHITESPACE@[8; 9)
+    BLOCK@[9; 43)
+      L_CURLY@[9; 10)
+      WHITESPACE@[10; 15)
+      LET_STMT@[15; 24)
+        LET_KW@[15; 18)
+        WHITESPACE@[18; 19)
+        BIND_PAT@[19; 22)
+          NAME@[19; 22)
+            IDENT@[19; 22) "foo"
+        WHITESPACE@[22; 23)
+        EQ@[23; 24)
+        err: `expected expression`
+        err: `expected SEMI`
+      WHITESPACE@[24; 29)
+      LET_STMT@[29; 41)
+        LET_KW@[29; 32)
+        WHITESPACE@[32; 33)
+        BIND_PAT@[33; 36)
+          NAME@[33; 36)
+            IDENT@[33; 36) "bar"
+        WHITESPACE@[36; 37)
+        EQ@[37; 38)
+        WHITESPACE@[38; 39)
+        LITERAL@[39; 40)
+          INT_NUMBER@[39; 40) "1"
+        SEMI@[40; 41)
+      WHITESPACE@[41; 42)
+      R_CURLY@[42; 43)
+  WHITESPACE@[43; 44)
diff --git a/crates/server/src/caps.rs b/crates/server/src/caps.rs
index 98499bb05..7456aea8a 100644
--- a/crates/server/src/caps.rs
+++ b/crates/server/src/caps.rs
@@ -5,6 +5,7 @@ use languageserver_types::{
     TextDocumentSyncKind,
     ExecuteCommandOptions,
     CompletionOptions,
+    DocumentOnTypeFormattingOptions,
 };
 
 pub fn server_capabilities() -> ServerCapabilities {
@@ -35,7 +36,10 @@ pub fn server_capabilities() -> ServerCapabilities {
         code_lens_provider: None,
         document_formatting_provider: None,
         document_range_formatting_provider: None,
-        document_on_type_formatting_provider: None,
+        document_on_type_formatting_provider: Some(DocumentOnTypeFormattingOptions {
+            first_trigger_character: "=".to_string(),
+            more_trigger_character: None,
+        }),
         rename_provider: None,
         color_provider: None,
         execute_command_provider: Some(ExecuteCommandOptions {
diff --git a/crates/server/src/main_loop/handlers.rs b/crates/server/src/main_loop/handlers.rs
index ec5421f06..ca5cd5ab1 100644
--- a/crates/server/src/main_loop/handlers.rs
+++ b/crates/server/src/main_loop/handlers.rs
@@ -314,6 +314,25 @@ pub fn handle_completion(
     Ok(Some(req::CompletionResponse::Array(items)))
 }
 
+pub fn handle_on_type_formatting(
+    world: ServerWorld,
+    params: req::DocumentOnTypeFormattingParams,
+) -> Result<Option<Vec<TextEdit>>> {
+    if params.ch != "=" {
+        return Ok(None);
+    }
+
+    let file_id = params.text_document.try_conv_with(&world)?;
+    let line_index = world.analysis().file_line_index(file_id)?;
+    let offset = params.position.conv_with(&line_index);
+    let file = world.analysis().file_syntax(file_id)?;
+    let action = match libeditor::on_eq_typed(&file, offset) {
+        None => return Ok(None),
+        Some(action) => action,
+    };
+    Ok(Some(action.edit.conv_with(&line_index)))
+}
+
 pub fn handle_execute_command(
     world: ServerWorld,
     mut params: req::ExecuteCommandParams,
diff --git a/crates/server/src/main_loop/mod.rs b/crates/server/src/main_loop/mod.rs
index da1121cb4..accb13878 100644
--- a/crates/server/src/main_loop/mod.rs
+++ b/crates/server/src/main_loop/mod.rs
@@ -31,6 +31,7 @@ use {
         handle_completion,
         handle_runnables,
         handle_decorations,
+        handle_on_type_formatting,
     },
 };
 
@@ -161,6 +162,9 @@ fn on_request(
     handle_request_on_threadpool::<req::DecorationsRequest>(
         &mut req, pool, world, sender, handle_decorations,
     )?;
+    handle_request_on_threadpool::<req::OnTypeFormatting>(
+        &mut req, pool, world, sender, handle_on_type_formatting,
+    )?;
     dispatch::handle_request::<req::ExecuteCommand, _>(&mut req, |params, resp| {
         io.send(RawMsg::Response(resp.into_response(Ok(None))?));
 
diff --git a/crates/server/src/req.rs b/crates/server/src/req.rs
index 999fdb7c2..881069b1f 100644
--- a/crates/server/src/req.rs
+++ b/crates/server/src/req.rs
@@ -14,6 +14,7 @@ pub use languageserver_types::{
     TextDocumentPositionParams,
     TextEdit,
     CompletionParams, CompletionResponse,
+    DocumentOnTypeFormattingParams,
 };