3 files changed, 120 insertions, 3 deletions

diff --git a/crates/syntax/src/ast/edit_in_place.rs b/crates/syntax/src/ast/edit_in_place.rs
new file mode 100644
index 000000000..06cde591d
--- /dev/null
+++ b/crates/syntax/src/ast/edit_in_place.rs
@@ -0,0 +1,105 @@
+//! Structural editing for ast.
+
+use std::iter::empty;
+
+use ast::{edit::AstNodeEdit, make, GenericParamsOwner, WhereClause};
+use parser::T;
+
+use crate::{
+    ast,
+    ted::{self, Position},
+    AstNode, Direction, SyntaxKind,
+};
+
+use super::NameOwner;
+
+pub trait GenericParamsOwnerEdit: ast::GenericParamsOwner + AstNodeEdit {
+    fn get_or_create_where_clause(&self) -> ast::WhereClause;
+}
+
+impl GenericParamsOwnerEdit for ast::Fn {
+    fn get_or_create_where_clause(&self) -> WhereClause {
+        if self.where_clause().is_none() {
+            let position = if let Some(ty) = self.ret_type() {
+                Position::after(ty.syntax().clone())
+            } else if let Some(param_list) = self.param_list() {
+                Position::after(param_list.syntax().clone())
+            } else {
+                Position::last_child_of(self.syntax().clone())
+            };
+            create_where_clause(position)
+        }
+        self.where_clause().unwrap()
+    }
+}
+
+impl GenericParamsOwnerEdit for ast::Impl {
+    fn get_or_create_where_clause(&self) -> WhereClause {
+        if self.where_clause().is_none() {
+            let position = if let Some(ty) = self.self_ty() {
+                Position::after(ty.syntax().clone())
+            } else {
+                Position::last_child_of(self.syntax().clone())
+            };
+            create_where_clause(position)
+        }
+        self.where_clause().unwrap()
+    }
+}
+impl GenericParamsOwnerEdit for ast::Struct {
+    fn get_or_create_where_clause(&self) -> WhereClause {
+        if self.where_clause().is_none() {
+            let tfl = self.field_list().and_then(|fl| match fl {
+                ast::FieldList::RecordFieldList(_) => None,
+                ast::FieldList::TupleFieldList(it) => Some(it),
+            });
+            let position = if let Some(tfl) = tfl {
+                Position::after(tfl.syntax().clone())
+            } else if let Some(gpl) = self.generic_param_list() {
+                Position::after(gpl.syntax().clone())
+            } else if let Some(name) = self.name() {
+                Position::after(name.syntax().clone())
+            } else {
+                Position::last_child_of(self.syntax().clone())
+            };
+            create_where_clause(position)
+        }
+        self.where_clause().unwrap()
+    }
+}
+
+fn create_where_clause(position: Position) {
+    let elements = vec![
+        make::tokens::single_space().into(),
+        make::where_clause(empty()).clone_for_update().syntax().clone().into(),
+    ];
+    ted::insert_all(position, elements);
+}
+
+impl ast::WhereClause {
+    pub fn add_predicate(&self, predicate: ast::WherePred) {
+        if let Some(pred) = self.predicates().last() {
+            if !pred.syntax().siblings_with_tokens(Direction::Next).any(|it| it.kind() == T![,]) {
+                ted::append_child(self.syntax().clone(), make::token(T![,]));
+            }
+        }
+        if self.syntax().children_with_tokens().last().map(|it| it.kind())
+            != Some(SyntaxKind::WHITESPACE)
+        {
+            ted::append_child(self.syntax().clone(), make::tokens::single_space());
+        }
+        ted::append_child(self.syntax().clone(), predicate.syntax().clone())
+    }
+}
+
+impl ast::TypeBoundList {
+    pub fn remove(&self) {
+        if let Some(colon) =
+            self.syntax().siblings_with_tokens(Direction::Prev).find(|it| it.kind() == T![:])
+        {
+            ted::remove_all(colon..=self.syntax().clone().into())
+        } else {
+            ted::remove(self.syntax().clone())
+        }
+    }
+}
diff --git a/crates/syntax/src/ast/make.rs b/crates/syntax/src/ast/make.rs
index 05a6b0b25..810c8d4c8 100644
--- a/crates/syntax/src/ast/make.rs
+++ b/crates/syntax/src/ast/make.rs
@@ -174,6 +174,11 @@ pub fn block_expr(
 pub fn expr_unit() -> ast::Expr {
     expr_from_text("()")
 }
+pub fn expr_literal(text: &str) -> ast::Literal {
+    assert_eq!(text.trim(), text);
+    ast_from_text(&format!("fn f() {{ let _ = {}; }}", text))
+}
+
 pub fn expr_empty_block() -> ast::Expr {
     expr_from_text("{}")
 }
@@ -390,6 +395,7 @@ pub fn token(kind: SyntaxKind) -> SyntaxToken {
     tokens::SOURCE_FILE
         .tree()
         .syntax()
+        .clone_for_update()
         .descendants_with_tokens()
         .filter_map(|it| it.into_token())
         .find(|it| it.kind() == kind)
@@ -544,6 +550,7 @@ pub mod tokens {
         SOURCE_FILE
             .tree()
             .syntax()
+            .clone_for_update()
             .descendants_with_tokens()
             .filter_map(|it| it.into_token())
             .find(|it| it.kind() == WHITESPACE && it.text() == " ")
@@ -569,13 +576,16 @@ pub mod tokens {
     }
 
     pub fn single_newline() -> SyntaxToken {
-        SOURCE_FILE
+        let res = SOURCE_FILE
             .tree()
             .syntax()
+            .clone_for_update()
             .descendants_with_tokens()
             .filter_map(|it| it.into_token())
             .find(|it| it.kind() == WHITESPACE && it.text() == "\n")
-            .unwrap()
+            .unwrap();
+        res.detach();
+        res
     }
 
     pub fn blank_line() -> SyntaxToken {
diff --git a/crates/syntax/src/ast/node_ext.rs b/crates/syntax/src/ast/node_ext.rs
index 52ac97c84..0b0d39a75 100644
--- a/crates/syntax/src/ast/node_ext.rs
+++ b/crates/syntax/src/ast/node_ext.rs
@@ -34,7 +34,9 @@ impl ast::NameRef {
 }
 
 fn text_of_first_token(node: &SyntaxNode) -> &str {
-    node.green().children().next().and_then(|it| it.into_token()).unwrap().text()
+    let t =
+        node.green().children().next().and_then(|it| it.into_token()).unwrap().text().to_string();
+    Box::leak(Box::new(t))
 }
 
 pub enum Macro {